Is it simply time for a new set of injectors?

[CROOZ1N]

The ohm out at 13 ohm when warm but the car has 125K. There seems to be some sluggishness in throttle response although ,this being my first Vette and the only C4 I've driven what do i know.

When you romp down on it the car seems to say... Wait, are you sure you want to go that fast? Really? Well hold on... Then she goes.
I added a bottle of Techron last week but before summer cruise seasons starts I'd rather try and do some PM work to head off any breakdowns.

For less than $ 200.00 is it worth the peace of mind to replace them or wait for a failure

Thanks again guys...

 

[Hib Halverson]

Have you run the fuel pressure tests and injector tests listed in the Service Manual?

If so, did the system meet pressure specs and did you find any bad injectors?

 

[aklim]

Ohm tests only tell you so much. The best way is to take the injectors out and have them tested every few years. That way, you KNOW for sure that something didn't go wrong. You could ohm my injectors and drive the car but you, or at least, I couldn't tell you that the basket on one of them was collapsed a little.

Before I go there, I would do a fuel pressure check. Hook up a gauge to the schrader valve and pressurize it. See what pressure you get and see how long it takes to get to 0. Tape the gauge to your glass and drive it with the hose to the FPR off and see what pressure you get.

 

[CROOZ1N]

Picked up a FP guage this evening and I'll post the results after testing.

 

[Hib Halverson]

All this stuff about taping a gauge to the windshield and driving is wasted effor.

If you do the test in the FSM you achieve the same results without driving.

Connect your gauge, turn the key on but do not start the engine. Observe the pressure and the gaguges behavior after the pump goes off. Consult the FSM for the pressure specs and, if your system meets the specs, you're ok.

If it dosen't meet the specs, ie: either the pressure with the key on engine off is too low or it doesn't hold, then you have a problem with either the injectors, FPR or, the pump or leakage.

In any of those cases, the FSM will suggest what to do.

 

[CROOZ1N]

Ok the pressure came up initially only to 21 PSI. But I had bled it off a bunch before attempting to screw on the pressure guage. I also missed the part about cycling the key a few times to get max pressure. After I started it the pressure came up to 40 psi and dipped slightly when reving. Maybe down to 35. After running for a bit I shut it down and at
6:38- 38 then rose to 40 the 42
6:43-45
6:50-45
6:58-42
7:15-32

I don't think I have a problem now but what is the life expectancy of the Multecs ?
I'd just hate to be on a trip somewhere and one or more give out. I guess though that I shouldn't borrow trouble. :ugh

Thanks Hib! As always you are the voice of reason.
Glad I didn't try and tape the guage to the windshield It's a pretty short line and I don't see as good as I usta!!

 

[aklim]

All this stuff about taping a gauge to the windshield and driving is wasted effor.

If you do the test in the FSM you achieve the same results without driving.

Connect your gauge, turn the key on but do not start the engine. Observe the pressure and the gaguges behavior after the pump goes off. Consult the FSM for the pressure specs and, if your system meets the specs, you're ok.

If it dosen't meet the specs, ie: either the pressure with the key on engine off is too low or it doesn't hold, then you have a problem with either the injectors, FPR or, the pump or leakage.

In any of those cases, the FSM will suggest what to do.

Is the pulse width the same whether the gear is in neutral or drive? I haven't looked at it before but I would think that under load, it takes more fuel at a given RPM than off load? Just curious. IOW, at 5000 RPM, does it use the same fuel whether you are driving or just revving?

 

[aklim]

Ok the pressure came up initially only to 21 PSI. But I had bled it off a bunch before attempting to screw on the pressure guage. I also missed the part about cycling the key a few times to get max pressure. After I started it the pressure came up to 40 psi and dipped slightly when reving. Maybe down to 35. After running for a bit I shut it down and at
6:38- 38 then rose to 40 the 42
6:43-45
6:50-45
6:58-42
7:15-32

I don't think I have a problem now but what is the life expectancy of the Multecs ?
I'd just hate to be on a trip somewhere and one or more give out. I guess though that I shouldn't borrow trouble. :ugh

Thanks Hib! As always you are the voice of reason.
Glad I didn't try and tape the guage to the windshield It's a pretty short line and I don't see as good as I usta!!

I would screw it back on and then cycle the switch to see. The pressure you have looks reasonable and it doesn't look like it is leaking anywhere.

Still, why not take the injectors out and have them cleaned and tested? Ohm tests and pressure test will not tell you if it is spraying well or not.

 

[boomdriver]

Ok the pressure came up initially only to 21 PSI. But I had bled it off a bunch before attempting to screw on the pressure guage. I also missed the part about cycling the key a few times to get max pressure. After I started it the pressure came up to 40 psi and dipped slightly when reving. Maybe down to 35. After running for a bit I shut it down and at
6:38- 38 then rose to 40 the 42
6:43-45
6:50-45
6:58-42
7:15-32

I don't think I have a problem now but what is the life expectancy of the Multecs ?
I'd just hate to be on a trip somewhere and one or more give out. I guess though that I shouldn't borrow trouble. :ugh

Thanks Hib! As always you are the voice of reason.
Glad I didn't try and tape the guage to the windshield It's a pretty short line and I don't see as good as I usta!!

Short.

They might ohm test ok, but they can crack and arc externally, clog, nozzels varnish and stick and over-all have poor performance. I've heard this several times, several places, "fuel injectors do not wear out, they just get dirty" but, nobody cleans and returns multecs for some reason.

For some really good info...go to You-Tube and search "fuel injectors" and you will see some FIC videos, test, and lots of great info that will help make a decision. As far as I know, they do not even service multec...just toss them in a box and forget 'em.
Your replacements will be probably be Bosch. Jon (FIC) will walk you thru the process.

Mine are bosch but have the "F" word:ugh on the other side. I need to talk to Jon about that...I did tell him it was a Corvette.. I started to sand the 4 letter word off before installing...

 

[CROOZ1N]

Nice boomdriver... My son has one of those F &*^ pony cars so I know of what you speak.
Jon has sent me a recommendation and i was seeking public opinion as to whether at 125K it was time to swap them out because of wear and age. And if there would be an added benefit of a little more umph under the right foot by changing them.
Again maybe i just don't need to borrow trouble or maybe I've already set the karma wheel/Murphy in motion....

 

[aklim]

Jon has sent me a recommendation and i was seeking public opinion as to whether at 125K it was time to swap them out because of wear and age.

And if there would be an added benefit of a little more umph under the right foot by changing them.
Again maybe i just don't need to borrow trouble or maybe I've already set the karma wheel/Murphy in motion....

I would.

Not without tuning. There would be a little more power if the old ones were tired and worn but if the old ones are good, I doubt you will see better anything. If you want more power, get bigger injectors and supporting items.

 

[boomdriver]

Nice boomdriver... My son has one of those F &*^ pony cars so I know of what you speak.
Jon has sent me a recommendation and i was seeking public opinion as to whether at 125K it was time to swap them out because of wear and age. And if there would be an added benefit of a little more umph under the right foot by changing them.
Again maybe i just don't need to borrow trouble or maybe I've already set the karma wheel/Murphy in motion....

For the money, theres really not a downside to installing a set of FIC injectors. He sends the injectors, all the runner gaskets, O-rings and his emergency only, top secret 24 hr a day phone number..
If your motor is stock or near stock, stay with the same size Bosch injector.

Even if there was'nt a noticable increase in performance, you can look at it as preventitive maintinence, and an opportunity to do some housekeeping on the intake area, update some vac hoses and other misc PM stuff. Good time to install an adjustable regulator too. Chances are that it will have better throttle response and idle smoother. I've yet to see anyone install these and not get some kind of improvement. This is one of those very rare deals where everyones been satisfied..

I did mine in the driveway in one day. Probably 6 hrs including the time on the bench cleaning and assembling the rails and double (triple) checking for leaks prior to completing the assembly.

My stock injectors had one that was arcing to the nearest thing and shorting that whole bank out. Stuck wide open. Flooded the motor so bad that there was 2 qts of gas in the oil pan....liquid gasoline blowing out the tail pipe. Why it did not explode I'll never know. Almost P'd my pants when I realized that I was sitting on an exhaust system FULL of gasoline and an engine trying to lite up......

Granted mine had 150,000 miles or more. There is no telling how long they had been gummed up and not spraying right.
I've heard of other multec malfunction that caused similar grief and when it came time, all I saw was positive comments about FIC and bosch-III injectors. The You-Tube vids sealed the deal. Injectors get dirty so slowly and the problems appear so slow that we just don;t notice until the engine no longer runs right and we can;t figure out why.
This may or may not solve the current problem, but it certainly can't hurt.

 

[tmkassin]

Even if the injectors are ok the seals are most likely shot. I replaced mine at 73000 to Bosch and what a difference! Most of the o rings on the original ones were wasted.

 

[Hib Halverson]

Ok the pressure came up initially only to 21 PSI. But I had bled it off a bunch before attempting to screw on the pressure guage. I also missed the part about cycling the key a few times to get max pressure. After I started it the pressure came up to 40 psi and dipped slightly when reving. Maybe down to 35. After running for a bit I shut it down and at
6:38- 38 then rose to 40 the 42
6:43-45
6:50-45
6:58-42
7:15-329

Unfortunately you did the test wrong. You don't start the engine when doing the fuel pressure test. You turn the key on but don't start the engine, ie: key on engine off, observe the pressure while you do this. The pressure should come up and peak then, as the pump turns off, fluctuate and hold.

The key factors to look for are: what is the pressure peak before the pump shuts off and once the pressure stops fluctuating, does it hold for a few minutes.

I don't think I have a problem now but what is the life expectancy of the Multecs ?

If there are no leaking injectors and none with electrical problems, you're injectors are still serviceable. I had the original-design Multecs in my old 88 Chevy Beretta which lasted the life of the vehicle, 140,000 miles. I have the newer Multec design in my 01 Camaro with 105,000 miles. If you run some Red Line SI-1 or Chevron Techron through the fuel system several times a year, the injectors will stay clean as new. In my cases, clearly, service life for injectors is more than 140,000 miles.

I'd just hate to be on a trip somewhere and one or more give out. I guess though that I shouldn't borrow trouble. :ugh

Personally, i wouldn't replace an injector until it fails.

Thanks Hib! As always you are the voice of reason.

Boy...have I got you fooled.

Glad I didn't try and tape the guage to the windshield It's a pretty short line and I don't see as good as I usta!!

There are occasions where one might want to watch fuel pressure while driving and rather than trying to tape a gauge to the front glass or run the hose into the interior, in my shop, I use a Waekon fuel pressure gauge which replaces the long length of hose with a wire. There's only a short length of hose from the fitting that goes on the test connection to a transducer. The transducer connects by a 12-foot wire to the display which you can put inside the car. Much easier and safer than taping a gauge on the windshield or trying to run the hose and gauge in to the interior.

 

[FISHAWK]

Injectors

I have been following this post, and I too have been considering replacing my injectors, My Vette is at 97k miles and I have already gone through the engine, when I bought the car it never idled smoothly, at first I thought I had a leaky injector but actually in the end I found out that most of the valves were bent (just enough to keep them from sealing completely) Anyway I have an adjustable regulator, it was on the car when I bought it, and my fuel pressure was fine every time I tested it so my injectors are probably good...Right? Anyway, my question was this: What size are the stock injectors on my 86 Alum head engine? Just in case I decide to replace them!:confused

 

[aklim]

Anyway I have an adjustable regulator, it was on the car when I bought it, and my fuel pressure was fine every time I tested it so my injectors are probably good...Right?

Anyway, my question was this: What size are the stock injectors on my 86 Alum head engine? Just in case I decide to replace them!:confused

Not necessarily. Mine were all good too. Testing found one of them had a collapsed filter basket and was spraying less than others in volume. Again, testing is the ONLY WAY that I can think of that will give you a certain answer as to whether it is good or not. You cannot tell volume from a pressure reading nor can you tell spray pattern without it being out. I can't understand why people are so resistant to sending it out every so often to make sure. Instead they put snake oils and listen to the Placebo effects to discern if the injectors are good or not. You can put all the cleaners you want and probably waste money or even put the can of stuff onto the fuel rail. Maybe it will clean out your injectors even but you can never be sure as to what it has cleaned. More important, you can not be sure if anything has been left behind. These easy methods are like sweeping a room in the dark. Sure, you have a pile of dirt but you don't know what is clean and what isn't in the room or how much is left to be done. Why not make it simple. Every 50K, take it out and have it cleaned and tested. If this is your beater car, I understand why you don't want to spend the money. Most Vettes are NOT a beater car so why not spend the money? Cost me $120 to know the results below and I know it will be good for at least another 3 years.

22 pph, I think but let Jon from FIC tell you for sure.

Here were my flow numbers

Before After
336 434
412 434
412 434.2
397 434
418 434
422 433.8
433 434.2
431 434

If you ohm it, the solenoids would come out ok. You can run it all day long but you cannot be sure as to whether it is the cam or the injectors. Pressure test it any way you want but again, no real way to know.

 

[JustCruzin]

Not necessarily. Mine were all good too. Testing found one of them had a collapsed filter basket and was spraying less than others in volume. Again, testing is the ONLY WAY that I can think of that will give you a certain answer as to whether it is good or not. You cannot tell volume from a pressure reading nor can you tell spray pattern without it being out. I can't understand why people are so resistant to sending it out every so often to make sure. Instead they put snake oils and listen to the Placebo effects to discern if the injectors are good or not. You can put all the cleaners you want and probably waste money or even put the can of stuff onto the fuel rail. Maybe it will clean out your injectors even but you can never be sure as to what it has cleaned. More important, you can not be sure if anything has been left behind. These easy methods are like sweeping a room in the dark. Sure, you have a pile of dirt but you don't know what is clean and what isn't in the room or how much is left to be done. Why not make it simple. Every 50K, take it out and have it cleaned and tested. If this is your beater car, I understand why you don't want to spend the money. Most Vettes are NOT a beater car so why not spend the money? Cost me $120 to know the results below and I know it will be good for at least another 3 years.

22 pph, I think but let Jon from FIC tell you for sure.

Here were my flow numbers

Before After
336 434
412 434
412 434.2
397 434
418 434
422 433.8
433 434.2
431 434

If you ohm it, the solenoids would come out ok. You can run it all day long but you cannot be sure as to whether it is the cam or the injectors. Pressure test it any way you want but again, no real way to know.

22lb @ 43.5 If your going to spend 120 on a cleaning spend 160 on reman bosch. If you have the multecs it's a wast of time and money to have them serviced anyway. Dump a can of crap in the gas and it will wash all the gunk in to your injector filter :ugh

 

[aklim]

22lb @ 43.5 If your going to spend 120 on a cleaning spend 160 on reman bosch. If you have the multecs it's a wast of time and money to have them serviced anyway.

Dump a can of crap in the gas and it will wash all the gunk in to your injector filter :ugh

Those are newer 42 pph injectors not the multec ones. I did check with Jon as to whether to replace or clean and he said it costs less to clean than getting a reman set.

Never done that before. I put Sea Foam or StaBil to keep the gas relatively fresh but I do drive it in the winter when the roads are good so I don't really need it that much

 

[JustCruzin]

Those are newer 42 pph injectors not the multec ones. I did check with Jon as to whether to replace or clean and he said it costs less to clean than getting a reman set.

Never done that before. I put Sea Foam or StaBil to keep the gas relatively fresh but I do drive it in the winter when the roads are good so I don't really need it that much

True, True...