Help! 90 wont start when hot

[tcxd40]

The L98 was the last gen of SB chevy engines. The LT1, same CID, however it was at the time the newest of the SB Chevrolet engines. Now we have the LS series.

tcxd40

 

[Phill]

I had a z28 with the L98 in it and it had the same problem. mine turned out to be starter heat soak.

 

[Gobbles]

How did you find out that it was the starter "heat soak". Did you replace the F.I. or anything and continued with the problem? When I bought it, the guy informed me to turn the key for a minute or so prior to starting to allow the fuel system to build pressure if I had an problems starting it. My main concern with it right now is the fact that it started acting up on me while driving it. It died on me at a stop light in the process of accelerating and acted as if it was misfiring. I got it to the gas station and let it sit for about 15 minutes and then it started up like it was fine. Dropped the kid of at a friends house which was about 2-3 minutes from the gas station. Turned the car of (hesitated on that one) and came back to start it back up and that is where it sat for the night due to not starting up. Came back the next morning and it started up just like a champ and had no problems on the way home. Although, I didn't take the scenic route due to being afraid of it shutting down on me again.

 

[Toy4Hal]

Do these answers/comments apply to an 89 as well?

Ironically, I'm trying to help a friend who has an 89 Corvette. The issue is the car "dies" like someone turned off the ignition upon acceleration from a stop, or "stumbles" at speed (wants to dies but recovers). I replaced the ignition module, and it seems a little better (at least will restart), but still has some "stumble", especially when the temperature is up at or above 200 degrees. It sounds very similar to what was asked here. Thanks.

 

[gmjunkie]

Hard hot start usually means faulty injectors .
Need to check the resistance of each injector.The ECM needs to "see" a certain resistance in each injector bank to pulse them.When hot , faulty injector resistance changes

Tacho problems very common to '90 models.
Generally a fault with the module in the dash cluster.

.Tachometer Filter Replacement - 1990 Vert - Corvette Forum

I don't Agree!! There are several things that can make L98 hard to start Warm,Not just the Injectors!! Weak Coil,Ignition Module Going South,Bad Distributer Cap,Bad Rotor,Bad Plug Wires,Spark Plugs,Wide or Narrow Gapped Plugs,Fuel Pump,Fuel Filter,Fuel Pressure Regulator,O2 Senors,Small piece of carbon in EGR,Temperature Senors,Vacuum Leaks,Low Compression and others!!Plus some of the above can also cause Tachometer problems!!

Get a FSM and trouble shoot by the book,without it a inexperienced mechanic will be just P*ss'n in the wind!!

 

[Gobbles]

So after changing the oil and letting her sit for 4-5 days, I decided I should start her up. Well I did and took a look around in the engine compartment. Well to my suprise, I found a spark plug loosely jiggling/vibrating. I've turned my attention to fixing that for now and will see if that fixes any other problems. Just informing all that might be interested. Thanks for the help thus far.


Tim

 

[Toy4Hal]

I don't Agree!! There are several things that can make L98 hard to start Warm,Not just the Injectors!! Weak Coil,Ignition Module Going South,Bad Distributer Cap,Bad Rotor,Bad Plug Wires,Spark Plugs,Wide or Narrow Gapped Plugs,Fuel Pump,Fuel Filter,Fuel Pressure Regulator,O2 Senors,Small piece of carbon in EGR,Temperature Senors,Vacuum Leaks,Low Compression and others!!Plus some of the above can also cause Tachometer problems!!

Get a FSM and trouble shoot by the book,without it a inexperienced mechanic will be just P*ss'n in the wind!!

Having similar issues with a friends 89, I have been "living" the chase!!! I spoke with GMJunkie last saturday about what I had done so far, and he advised a few more steps. So, here is what I did and where I'm at:

Original Issue: the car "dies" like someone turned off the ignition upon acceleration from a stop, or "stumbles" at speed (wants to dies but recovers).

Replaced Ignition Control Module. Replaced rotor and cap. Replaced coil.

Thought it was solved but, when hot (220 degrees) stumbled in city starts.

Took to shop to replace fuel filter & fuel pump (need lift for filter). Car "stumbled" all the way to the shop at each stop light. As long as I kept RPMs up, and 'feathered' the accellerator to do slow start, I could get to next light. (this is before fuel pump and filter).

After fuel pump and filter, cal would not start at all!!!! Lots of crank but no connection. Good fuel pressure, and there was spark. Would not start. Went for lunch, came back, she started. Would idle for a few seconds, then cut out. Had the computer plugged in and saw no codes or issues. Correct voltage readings everywhere.

Replaced (I think it's called) Throttle Control Module. No change.

Stumped! Towed it to dealer. They have diagnosed it as bad ECM. Also, there are 2 very bad injectors with the rest being "marginal". (BTW: car idles smooth when she is running).

They have replaced the ECM but I'm reluctant to drive her home to do the injectors myself for fear that the bad injectors will blow the ECM again. (Dealer wants a fortune to do the injectors, like $200 each plus labor).

Sorry for the long message but the devils always in the details. (I'm living the list that GMJunkie stated!)

So, any thoughts or comments about driving her 40 miles before doing the injectors? Or other thoughts?

Thanks. Hal

 

[gmjunkie]

Stumped! Towed it to dealer. They have diagnosed it as bad ECM. Also, there are 2 very bad injectors with the rest being "marginal". (BTW: car idles smooth when she is running).

They have replaced the ECM but I'm reluctant to drive her home to do the injectors myself for fear that the bad injectors will blow the ECM again. (Dealer wants a fortune to do the injectors, like $200 each plus labor).

Sorry for the long message but the devils always in the details. (I'm living the list that GMJunkie stated!)

So, any thoughts or comments about driving her 40 miles before doing the injectors? Or other thoughts?

Thanks. Hal

If it has 2 bad injectors,I question the ECM replacement!! Whats with the injectors anyway,Low Ohm-age,Leaking Down,Clogged???

 

[John Robinson]

Add to the list

I have just had my opti replaced and yes I know you have a distributor but I think what happened to me is relevant. I normally do the work on my car myself but after chasing my A** for several weeks and still havin problems it was time for me to pay for a diagnostic on the car. Here is were it gets interesting they found the Opti was bad so I left it with them to replace it. Sure am glad I did because they went through 3 opti's and two tear downs and the last time they got it together it would not run or start it said there problems with the new opti. The mechanic was about to pull it apart again when one of the other mechanics took a look at the wire connections on the ignition coil wire etc. What he found was that the coil wire connector was corroded and not making good contact they cleaned all the rest of the ignition connectors and the engine started and ran great. Another problem caused by time and moisture.:L

 

[gmjunkie]

What he found was that the coil wire connector was corroded and not making good contact they cleaned all the rest of the ignition connectors and the engine started and ran great. Another problem caused by time and moisture.:L

Thats EXACTLY why the first thing I do is is Pull any Codes,and Clean every Ground,Fuse and Wiring plug under the Hood!!
Over 90% of the time,Problem solved with No Parts and 3-4 hours of my time!!

 

[Toy4Hal]

If it has 2 bad injectors,I question the ECM replacement!! Whats with the injectors anyway,Low Ohm-age,Leaking Down,Clogged???

Number 3 read 800 Ohm
Number 8 read 400 Ohm

All others were in the 1,300 to 1,350 Ohm range.

Car has about 110k miles and very poorly maintained. I'll address the maintenance going forward but now just need to get it home so I can work on it.

Thanks. Hal

 

[Toy4Hal]

What he found was that the coil wire connector was corroded and not making good contact they cleaned all the rest of the ignition connectors and the engine started and ran great. Another problem caused by time and moisture.:L

Good thoughts and comments, John. We did do a continuity test on the wires in/around the distributor, especially focused on the wires on both sides of the ignition module. All tested good. Had good spark as well, and good fuel pressure. After all the parts we had done, we we're stumped (we includes a good mechanic friend with all the right test gear). We suspected the ECM but, like your opti, we know that you cannot return it once you buy it. Thus, why we let the dealer work it. The dealer did the work to find the ECM and injector issues using the GM diagnostic equipment.

Hal

 

[vetteoz]

I don't Agree!! There are several things that can make L98 hard to start Warm,Not just the Injectors!!Weak Coil,Ignition,O2 Senors ..............Low Compression and others!!Plus some of the above can also cause Tachometer problems!!

He states in his other post that it will hot start with fuel sprayed in the TB.Sounds like the common hot resistance problem with old injectors to me.
02 sensor has no part in startup;only comes into play when engine goes closed loop.

'90 tacho problem is well documented around the C4 Forums.

 

[Toy4Hal]

Fuel Injectors Replaced

I thought it appropriate to post the continued status on the 89 I spoke of which would not continue to run and was finally was diagnosed with 2 very bad injectors. I did buy and install a set of Bosch III injectors from South Coast Fuel Injectors.

I can't say enough good things about these people. They were available at all hours to help me (my 1st time doing this) get the injectors installed right and not leaking.

The instructions previously posted by someone else on this site were very good; a few variants such as a solid vacuum line to the brake booster and the need to disconnect a few more parts at the front in order to get to the inside bolt on the passenger side of the fuel rail. But, all in all, if you take your time, anyone can do this. Just don't rush!!

So, the car is back together, runs good, idles nice, etc. However, fuel usage is way up!!! I don't personally have a history driving this car but I was a little concerned with fuel mileage while I drove it for the few days after the job. But, I was driving on city streets and putting my foot into her to see if she died on hard acceleration. Nope. She runs fine.

The owner of the car is now telling me she is seeing freeway mileage in the high teens while cruising at about 60, where she was used to seeing high 20's in the same circumstances. So, back to my "experts"! Any advice?


Let's recap what has been done (in this sequence)

• Ignition module replaced.
• Cap, rotor, and coil replaced.
• Fuel filter replaced.
• Fuel pump replaced.
• Throttle control valve replaced.
• ECM was replaced (by the dealer).
• Original factory injectors replaced by Bosch III 22 lb. injectors.

This is where she sits. Runs great, runs strong (for an 89). But using a lot of fuel. Ideas?

Thanks in advance. Hal

 

[Toy4Hal]

I did buy and install a set of Bosch III injectors from South Coast Fuel Injectors.

I can't say enough good things about these people. They were available at all hours to help me (my 1st time doing this) get the injectors installed right and not leaking.

Sorry for mis-stating the name of company that sold me the injectors and supported the installation. The company is "South Bay Fuel Injectors". Great people!. Sorry for the confusion.
Hal

 

[Hib Halverson]

First: ignore some of the pressure here to buy injectors...at least for now.

It is true that hard starting when hot, can be an injector problem but, proper diagnosis is the first step...then buy injectors if the troubleshooting leads that way.

Now....when you have this hot start problem, what happens when you put the ECM into "clear flood" mode by flooring the throttle then cranking? Will the engine start and run and do you smell gasoline from the exhaust? If "yes" you may have injector issues. If "no" the problem might be injectors, but may also be some other issue unrelated to them.

In any event, what'd I'd not do is put new injectors in before performing a proper diagnosis.

As suggested by others here, use the Haynes manual to line your cat box then buy a Factory Service Manual for a 90. Look on eBay or Craig's list for a used one but...avoid any with a white cover (the sign of a "preliminary copy") and only buy the "release" version with a red cover. If you can't find one used, get new ones from Corvette Central.

Once you get the book, you need a fuel pressure gauge. Then read the FSM's section on fuel pressure tests. They are the initial step for diagnosing a possible injector problem. The books also contain instructions on how to test the electrical part of each injector. Further, they also have diagnostic information about what to do if this hard starting is caused by something other than an injector problem.

Good luck.