High RPM's on start up

[joshwilson3]

If you plan on checking and adjusting min air speed knowing your situation, you will want to push up the IAC counts by backing out the idle screw. Just be careful that you don't fully seat the throttle plates. The screw tip is the right stop point, not the throttle plates in the bores. I suspect you will need to close the plates more than that required with the proper injectors. Good luck, and keep us posted on the results.

Okay thanks. I've got a large print out on setting min air.

One thing that was always in debate. Is with an automatic. Do you set min air in drive, or park? Lots like to argue, but I'm thinking setting it in drive is correct.

And do you disconnect the EST? Some say you do, others say not to.

 

[TedC]

Follow these instructions. They are out of my 1989 GM factory service manual. I just combined the steps into a logic flow. Just remember that any adjustment to timing impacts min air speed, any min air adjustment impacts TPS setttings. So there is a proper sequence that must be followed. Adjusting in drive makes no sense to me. The engine barely runs (you shut off all IAC air flow) so be prepared to manually open the throttle plates to keep it running. No way would I do this in drive.

Throttle Body Adjustments for 1989 L98 Corvette

Start and run engine until it reaches operating temperature (closed loop)
Check and set engine timing to 6 degrees of advance with EST wire disconnected
Check and set throttle position sensor (TPS) to .54 (+/- .08) volts at idle
Jumper terminals "A" and "B" on the ALDL
Turn ignition key on and do not start engine
Wait 60 seconds so that the idle air control (IAC) motor fully extends
Without turning ignition key off, remove connector from IAC motor
Turn ignition key off and disconnect ALDL jumper
Start and run engine until it reaches operating temperature (closed loop)
Remove minimum idle air cap if required
Adjust idle speed to 425 (+/- 25) rpm in either in park or neutral
Turn ignition key off and reconnect EST wire and IAC motor
Check and set throttle position sensor (TPS) to .54 (+/- .08) volts at idle
Reset ECM by disconnecting and reconnecting power at battery terminal
Depress accelerator pedal slightly
Start and run engine for 5 seconds
Turn ignition key off for 10 seconds
Drive vehicle to assist in ECM reprogramming

 

[joshwilson3]

I've got the min air set. And I still get the high RPM rev on start up. I guess I'll get a cigar and blow smoke into the booster line for a while and see if that shows up anything with regards to a vacuum leak. But I think if it was a vacuum leak, I'd have idle problems too and not just a start up flare problem.

I'll probably check around the shops to see if any of them would have any idea as to what it could be for them to check. As I don't plan on spending a ton for them to check 100 things under the hood.

 

[TedC]

Did the idle speed drop down when fully hot? What are the IAC steps when fully hot? Could you get these steps to fall between 15-20?. Before, you had posted that the ECM desired speed was not being reached even with a fully closed IAC. I agree, this doesn't appear to be a vacuum leak issue. Would be nice to hear from L98 owners who have 24# injectors if they ran into similar issues.

 

[joshwilson3]

Did the idle speed drop down when fully hot? What are the IAC steps when fully hot? Could you get these steps to fall between 15-20?. Before, you had posted that the ECM desired speed was not being reached even with a fully closed IAC. I agree, this doesn't appear to be a vacuum leak issue. Would be nice to hear from L98 owners who have 24# injectors if they ran into similar issues.

The car was already hot when I ran my scan while idling after I was done setting the min air. But the RPM's were like 625-650. The ECM was calling for 625. The IAC steps were around 15 most of the time. I guess the PO didn't set it right as that cap was already removed.

I don't think it is the injectors. The PO installed the injectors somewhere around 6+ years ago. I didn't have any problems with the RPM spike on start up until several months ago right after it was down for a month and a half. When I had started driving it I noticed it kicked into gear hard when I shifted from park. Then I noticed the problem was on start up the RPM's were high when I shifted into drive. So now I wait a couple of seconds for the RPM's to drop before shifting.

I do notice sometimes on the warm start up when the RPM's shoot up that sometimes you can hear a brief rumble from the exhaust when the RPM's peak.

 

[boomdriver]

Did the idle speed drop down when fully hot? What are the IAC steps when fully hot? Could you get these steps to fall between 15-20?. Before, you had posted that the ECM desired speed was not being reached even with a fully closed IAC. I agree, this doesn't appear to be a vacuum leak issue. Would be nice to hear from L98 owners who have 24# injectors if they ran into similar issues.

I have 24-lb/hr bosch-III injectors in my L98. I went up a size because the induction is much larger and the exhaust is also.

On cold start mine cranks over 2 seconds then lites off and most times idles at 700 and quickly settles to 600-650. I always run for 1-2 minutes or until 120+ degrees before moving the car. IF I use ANY throttle during this warm up period, the idle might go up to 8-900 but settle back to 650 avg after it hits its normal ECM mode shift of 158 on the gauge.

Once warm, it fires instantly and initial idle may go to 800 for 2 seconds then quickly down to 600-650. I turn on the a/c after a few seconds and that may drop cold idle 50 rpm, but not a warm idle.

The larger injectors had zero effect on idle speed. Reading the plugs, the current colors indicate that 24 lb/hr is perfect for this particular engine. It might even be able to use 26. I have serious doubts that 24 are good for a box-stock engine. I would certainly be looking at spark plug colors to see if I was on a slow road to major repairs with a rich engine. If you have any doubts as to the plug colors and condition, take them to a motorcycle shop, dirt bikes especially and ask them to look.
The PO probably installed those with the carb mentality of bigger is better. Not true in fuel injection and computer controls. Rich means damage. Excessive wear, contaminated oil, clogged cats. Might run ok, but it'll wear itself out lots sooner. Precision fuel control is why we see gas motors with 250,000 miles that still do not burn lots of oil. Carb motors were throw aways at 100,000. Fuel monitoring/management is why things got better.


The cold start-up in a L-98 is always with basics and not ECM assisted closed loop,. so the cold start system is suspect IF the air system is found to be healthy. Cold start is simple and easy to have fault. The time/temp sensor in the front of the intake (if so equiped) is the signal source to the cold start valve. If those connections or that sensor are dirty or faulty, its easy to see a spike in fuel at lite-up. That is possibly the "flare". As soon as the engine runs, the cold start is d/c...after a very few seconds at most. Point is, if the CS system is not right, then that initial lite-up is like having the choke on....all fuel and no air. Its worth cleaning the contacts at least. Its easy enough to D/C the cold start valve to see if that makes a difference cold or warm.

 

[joshwilson3]

Boomdriver,

Mine is an 89. It doesn't have a cold start thing.

I guess the good thing is I don't think it has alot of miles on those injectors. How fast will it damage the engine?

I was looking at doing the master cylinder. I guess I could get some injectors and go ahead and replace them if it is causing engine damage

 

[boomdriver]

Boomdriver,

Mine is an 89. It doesn't have a cold start thing.

I guess the good thing is I don't think it has alot of miles on those injectors. How fast will it damage the engine?

I was looking at doing the master cylinder. I guess I could get some injectors and go ahead and replace them if it is causing engine damage.

the injectors really are a "do it yerself" job....quite easy with decent tools. It takes patience more than skill. Even then, with tools, it only takes maybe 1 hour to have them on the floor...A little longer to reassemble because of the need to check everything twice. The last thing you want is a small gas leak when its totally assembled...
Shops charge about $350 to $450 for labor to do injectors. Injectors are about $225 a set at FIC. Good, reliable products with outstanding customer service. Look at YouTube for fuel injector videos. FIC made most of them. Very informative.

As far as engine damage, its not going to be fast or anything to be alarmed about. Its not an emergency but it will shorten the life of an engine if its not addressed. Rich fuel washes off the oil film on the cylinders and that is how the wear takes place. Its slow,and minimal but it does occure. Rich fuel also gets into the oil thru normal means and because gasoline is a solvent that lessens the oils life and generates sludge faster. Again, its not an emergency. Its just something to be aware of. If the engine is utilizing the fuel, there is NO problem.
The plug color will help tell about that. You can throw all the fuel you want in a diesel and it goes faster. But a gas engine wants more air when there is more fuel. Sometimes it makes the engine run worse, not better. Its all about keeping the 14.7:1 air/fuel ratio, or as close as the ECM can get.
Look at the performance of the same size engines from 1970 to todays....much much more efficient today with more power, longer life and less emissions. Whats different? The fuel management. I hate to think of how bad the avg ratio was on a 1969 muscle car....No wonder there is smog.

If you have an adjustable fuel regulator, just turn the pressure down to under 40 psi. Thats what I was told if I needed to go back to 22 lb/hr. That is what I was told by the guy that sells LOTS of injectors to members here. The difference between the 22 lb and the 24 lb is a few psi of pressure.

Before you start worrying about changing injectors, look at the plugs. The evidence will be there and there is absolutely no disputing what is happening in the engine when looking at the color of the spark plug insulator. It should be off-white to a tan color. Brown is acceptable for a car that does more city driving, but a car that see's the freeway should be a lighter color. Anything darker than lt brown is running richer than you want..
If the plugs are dry and dark that is rich fuel. Dark & wet is probably oil burning confirmed by oil usage. If its not using any oil and the plugs are wet, thats real rich.
I think NGK has a good plug color chart.

If your motor does not have the cold start injector, it uses the injectors to richen the mix for start-up. Where that signal comes from on yours, I do not know.

The master cylinder is something that I need to do also. My pedal went to the floor one time recently, then never did that again. I want to replace that master cylinder before it happens again. I am looking for a set of "speed bleeders" for the calipers so flushing the system and bleeding will be a simple one man job with no mess. Just can;t find the right size for the vette calipers. Speed bleeders have a build in check valve so there is no need to close them when letting off the pedal. just open the valve, pump the pedal and its done. use a hose to a bottle to catch the fluid thats spit out.

 

[joshwilson3]

The spark plugs I pulled last year that were on there for a while were carbon fouled. I pulled a plug a few months ago and just noticed a small brown stain on the porcelain.

I've got some Bosch III's ordered from FIC. Looks like you don't need the clips on these injectors. You put them in the manifold first, then put the rail on. I've got some Palmolive soap to lubricate the injector o-rings as mentioned on FIC's site.

I've already got the plenum off and all the runner bolts out. Next I'll have to pull the rail so I can finish getting the runners out so I can clean the runners and the plenum with brake or carb cleaner.

Before I pull the rail. I'm going to prime the pump and look for rail leaks. I haven't seen anything leaking, and if I don't see anything leaking when I check. Then I won't tear the rail down to replace the o-rings. I'll probably go ahead and replace the send and return line o-rings though.

 

[boomdriver]

The spark plugs I pulled last year that were on there for a while were carbon fouled. I pulled a plug a few months ago and just noticed a small brown stain on the porcelain.

I've got some Bosch III's ordered from FIC. Looks like you don't need the clips on these injectors. You put them in the manifold first, then put the rail on. I've got some Palmolive soap to lubricate the injector o-rings as mentioned on FIC's site.

I've already got the plenum off and all the runner bolts out. Next I'll have to pull the rail so I can finish getting the runners out so I can clean the runners and the plenum with brake or carb cleaner.

Before I pull the rail. I'm going to prime the pump and look for rail leaks. I haven't seen anything leaking, and if I don't see anything leaking when I check. Then I won't tear the rail down to replace the o-rings. I'll probably go ahead and replace the send and return line o-rings though.

Plan on doing rail O-rings...if you lift the rail then you will have to. Thats the easiest part of the repair. The injector rings are more difficult to mount and then mount 4 injectors together.
The rail is NOT a solid assembly and as soon as it moves all the seals twist and tear away at the joint O-rings. You will have a leak if you don;t replace those joint o-rings. They are simple. Take the runners off first. Then the 4 rail bolts and lift the rail straight up with a rocking motion to loosen the bank of injectors. They will be stiff but they will pop out by rocking.
Reassemble with vasoline and once an O-ring is installed, do not twist the injector around or allow the rail tubes to twist. Thats what damages o-rings and causes leaks. After getting the rail bolted down on all 8 injectors, BEFORE adding runners, connect the fuel lines and pressurize with the key "on" and get fuel pressure. This needs to be 40 psi and it needs to stay near 40 psi for 1/2 hr before proceeding to the runners. This is the way to test for leaks/seals before adding all the parts that will have to come off if a leak shows up late in the repair.

It only takes another 30 minutes to do the rail o-rings and have it all done right.

PS
don't get brake parts cleaner or degreaser anywhere near the fuel injection harness. It hardens the wire insulation and will cause bare wire to appear in the harness. Do all that cleaning on the driveway, away from the motor. Runners are easy to remove with a torx bit in a driver extension. I'm replacing my torx with cap screw head metric bolts.

 

[joshwilson3]

Plan on doing rail O-rings...if you lift the rail then you will have to. Thats the easiest part of the repair. The injector rings are more difficult to mount and then mount 4 injectors together.
The rail is NOT a solid assembly and as soon as it moves all the seals twist and tear away at the joint O-rings. You will have a leak if you don;t replace those joint o-rings. They are simple. Take the runners off first. Then the 4 rail bolts and lift the rail straight up with a rocking motion to loosen the bank of injectors. They will be stiff but they will pop out by rocking.
Reassemble with vasoline and once an O-ring is installed, do not twist the injector around or allow the rail tubes to twist. Thats what damages o-rings and causes leaks. After getting the rail bolted down on all 8 injectors, BEFORE adding runners, connect the fuel lines and pressurize with the key "on" and get fuel pressure. This needs to be 40 psi and it needs to stay near 40 psi for 1/2 hr before proceeding to the runners. This is the way to test for leaks/seals before adding all the parts that will have to come off if a leak shows up late in the repair.

It only takes another 30 minutes to do the rail o-rings and have it all done right.

PS
don't get brake parts cleaner or degreaser anywhere near the fuel injection harness. It hardens the wire insulation and will cause bare wire to appear in the harness. Do all that cleaning on the driveway, away from the motor. Runners are easy to remove with a torx bit in a driver extension. I'm replacing my torx with cap screw head metric bolts.

For some reason I wasn't able to pull the runners. They kept hitting something. It looks like the runner on the passenger side was hitting the fuel lines from the rail when I tried to pull it. I'll look at it again to see if I can get the runners off before I pull the fuel rail.

When I talked to FIC, they told me not to mess with the rail o-rings if they aren't leaking. As they said it was a pain. But I guess I could replace them if it isn't too hard.

I'm assuming carb cleaner would be better to clean the intake instead of brake cleaner? Just don't want to damage something.

Do you know how much torque the fuel rail bolts get?

I remember John from FIC mentioning if you take the rails apart. To clean them with Gumout and rinse with simple green and blow it out with compressed air. Though If I did that, I probably wouldn't clean the FPR as I wouldn't want to mess it up.

A pic I found:

 

[TedC]

Torque specs:
Rail attachment bolts 15#
Fuel tube bracket 25#
Fuel line nuts 20#
Plenum/Runners 25#
Brake Line 9#
Throttle Body 18#

Comments:
I did not need to replace the rail o-rings. Used fuel injector cleaner to clean out the rails then compressed air. The two fuel rings had to be replaced. These were not in the kit from FIC. Make sure ALL of the injectors are properly seated before tightening the rail down. If you are using Bosch IIIs, then you will not reuse the injector retainer clip. Once you have the fuel rail installed, check for leaks. Prime the rails (ignition on) a few times and open up the schrader valve to let the air escape.

 

[joshwilson3]

Torque specs:
Rail attachment bolts 15#
Fuel tube bracket 25#
Fuel line nuts 20#
Plenum/Runners 25#
Brake Line 9#
Throttle Body 18#

Comments:
I did not need to replace the rail o-rings. Used fuel injector cleaner to clean out the rails then compressed air. The two fuel rings had to be replaced. These were not in the kit from FIC. Make sure ALL of the injectors are properly seated before tightening the rail down. If you are using Bosch IIIs, then you will not reuse the injector retainer clip. Once you have the fuel rail installed, check for leaks. Prime the rails (ignition on) a few times and open up the schrader valve to let the air escape.

Thanks for the torque specs. Since I won't have a way to measure torque on the fuel send/return line nuts. What I'll do is mark a side of the nut and take a pic. Then when I tighten them, I'll tighten it back to where it was before I messed with it. Though, I'll have new o-rings on those lines.

I'll decide later if I pull the rail apart. But I'm thinking it isn't too big of a deal. I just don't want to mess up an oring.

 

[boomdriver]

Thanks for the torque specs. Since I won't have a way to measure torque on the fuel send/return line nuts. What I'll do is mark a side of the nut and take a pic. Then when I tighten them, I'll tighten it back to where it was before I messed with it. Though, I'll have new o-rings on those lines.

I'll decide later if I pull the rail apart. But I'm thinking it isn't too big of a deal. I just don't want to mess up an oring.

The rail o-rings are insurance. Its just a gamble to get that close to them and not replace, and end up with a leak somewhere down the road.

The thing is, that the round tubes in the rails allows the whole assembly to twist and swivel as you lift it off. It won;t come apart because there are retainers on the tubes, but it will twist around and that CAN disturb an O-ring and its ability to seal. Old o-rings that have been subjected to yrs of ethanol blended gasoline can be dry and brittle sometimes.

Two things about O-rings...
Don;t "roll" them in place and don;t twist the part inside the O-ring. Lubricate well and let the ring "slip" in place by stretching and sliding. Lube the bottom of the injectors well because you have to "pop" 4 inj in at a time and there will be a click/snap/or a pop as they settle in. Actually, I forget if the top or bottom goes in first on the Bosch-III...Follow Jons instructions and its a cake-walk.
You'll feel it when they pop in place.. Thats why I use vasoline and not soap in the baseplate & rail. I also wipe out the inj holes in the baseplate with carb cleaner, rags and a Q-tip so the hole is as clean as possible.

I'd use some plain soap & water to clean the rail. The plenum and runners may require some carb cleaner and a bottle brush inside.. Just keep all the cleaners away from the electrical and other misc wiring/electrical parts. This is a good time to replace any vac tubing thats old and dry.
The FPR does not need to be cleaned, just the ports. Do this with the diaphram out. Protect that rubber diaphram. The rest is just metal.

I've noticed that some HD degreasers and solvents will damage the exterior finish on the rail tubing. Thats a paint of some sort and some harsh cleaners make it peel off. Thats why simple is better. There will be more housekeeping to do on the intake baseplate than on the rails. As long as the rails assemble clean, thats the goal. But like TedC says...get the rails on, fuel lines on and pressurize the system to test for leaks. Let it sit for a little while under pressure and try to have the injectors where they need to be so they don;t have to be twisted once mounted. Thats bad for the o-rings.

This is really easier than it sounds. I did mine in the driveway in one morning.

Your runners try to hang up on the valve cover edges and everything else. make certain that you have the odd bolt out, the one on the reverse side of both runners. That one causes lots of aggrevation because many guys don't see it and can't figure out why the runners won;t come off even with all the front bolts out. There is one thats accessed from the opposite side on both runners. Look at the runner flange ends for the odd bolt. The backwards bolt. Driver side access is past the EGR valve with odd assortment of extensions, and the other one is the front edge of the passenger side runner that you access from the driver side around where the T-body would be.

Another reason for diving in this deep is to have all these potential sources of air leaks examined. New gaskets are always a good thing.
Also, I wipe a thin coat of never-seize compound on the new runner/plenum gaskets so they do not glue themselves to the metal. This prevents them from having to be scrapped off next time.

I've heard mixed reviews on Accel injectors but I DO know the Bosch III are a quality product. I wish that all business offered this level of customer service.

 

[joshwilson3]

The runners kept hitting the fuel rail. I have all the bolts out. But I messed with it for a while and it looks like the rail will need to be pulled before I can finish removing the runners.

I'm also gonna reseal a few intake bolts. Have a small puddle of oil at the rear of the driver top intake below the runner. The intake gasket/seal needs replacing, but I'm not gonna bother with that. But I can easily reseal a few intake bolts while the runners will be pulled.

I'll probably lube the orings before I put them on the tubes. The dealer has the orings for the send/return lines in stock. So, I'll pick those up as well.

 

[boomdriver]

The runners kept hitting the fuel rail. I have all the bolts out. But I messed with it for a while and it looks like the rail will need to be pulled before I can finish removing the runners.

I'm also gonna reseal a few intake bolts. Have a small puddle of oil at the rear of the driver top intake below the runner. The intake gasket/seal needs replacing, but I'm not gonna bother with that. But I can easily reseal a few intake bolts while the runners will be pulled.

I'll probably lube the orings before I put them on the tubes. The dealer has the orings for the send/return lines in stock. So, I'll pick those up as well.

DUH :ugh ! I forgot the obvious...! your Accel injectors are probably shorter than the stock injectors, so yes, the rail will have to be loosened. When everything is stock, the runners have to be "manipulated" a certain way to remove them...
The Bosch inj are shorter as well, so it'll go back together in a similar order of assembly.

Intake bolts is a GREAT idea !

I think thats something that gets overlooked way too often. So easy to do and there is little risk when pulling one at a time and cleaning and sealing. Keeps leaks down to a minimum.

If you have the tools, run a tap into the bolt holes to clean. I was amazed at how much difference that makes when torqueing down bolts later. All this aluminum stuff corrodes inside and old sealer and dirt make the threads dirty. After I stripped out a few aluminum parts from over tightening, I now run the tap thru aluminum threads so I get a good torque and don;t damage the fragile threads. Made a world of difference in the way the bolt goes in and how it feels when getting tight.

 

[joshwilson3]

DUH :ugh ! I forgot the obvious...! your Accel injectors are probably shorter than the stock injectors, so yes, the rail will have to be loosened. When everything is stock, the runners have to be "manipulated" a certain way to remove them...
The Bosch inj are shorter as well, so it'll go back together in a similar order of assembly.

Intake bolts is a GREAT idea !

I think thats something that gets overlooked way too often. So easy to do and there is little risk when pulling one at a time and cleaning and sealing. Keeps leaks down to a minimum.

If you have the tools, run a tap into the bolt holes to clean. I was amazed at how much difference that makes when torqueing down bolts later. All this aluminum stuff corrodes inside and old sealer and dirt make the threads dirty. After I stripped out a few aluminum parts from over tightening, I now run the tap thru aluminum threads so I get a good torque and don;t damage the fragile threads. Made a world of difference in the way the bolt goes in and how it feels when getting tight.

I don't have a tap. What size is needed?

I had pulled a front intake bolt last year and resealed it. I didn't tap it, but there was a tone of gunk in there.

I may see if Napa has the tap as I wouldn't want to buy a set.

 

[TedC]

This would be the best time to remove the intake, clean the threads and bolts, and install a new intake gasket if you suspect an oil leak. Potential for the old thread sealant to fall into the engine if the bolts are removed and/or just retorqued.

To tighten bolts that require extensions, you can use this formula.
M1 = M2 x L1 / L2
M1 is the torque setting of the wrench
M2 is the actual torque applied to the nut
L1 is the normal length of the wrench
L2 is the extended length of the wrench

 

[TedC]

What I did on mine was to use the intake torque sequence and check each bolt at 25#. 35# is the right torque specification. This way I avoided breaking any thread seals if they were tight. I had two bolts that turned (#10 and #8), so I upped the torque to 30#, then 35# on just these two bolts. I did not remove any intake bolts.

12 - 11 - 4 - 1 - 5 - 6
FRONT
10 - 9 - 3 - 2 - 7 - 8

I rechecked the two bolts several months afterwards and they were still tight to specification.

 

[joshwilson3]

What I did on mine was to use the intake torque sequence and check each bolt at 25#. 35# is the right torque specification. This way I avoided breaking any thread seals if they were tight. I had two bolts that turned (#10 and #8), so I upped the torque to 30#, then 35# on just these two bolts. I did not remove any intake bolts.

12 - 11 - 4 - 1 - 5 - 6
FRONT
10 - 9 - 3 - 2 - 7 - 8

I rechecked the two bolts several months afterwards and they were still tight to specification.

Thanks, I'll check the torque first in the sequence you did. I'll start at 25 ft/lbs then move up to 35 ft/lbs.

And I've noticed some oil residue in the middle part of the intake on top also on the driver side:

The passenger side is dry.

Good thing I'm replacing these injectors. I noticed a small spring at the top of one of the Accel injectors. I don't know if the spring was inside the injector and worked its way out, or if the spring got in the fuel system somewhere. I'm gonna go ahead and break the fuel rail down and clean it.