My 1990 Corvette 6-speed is giving me fits. When I first start it up, it runs fine, idles properly. After I drive it a few miles, it either won't start or when it does start, it has a loping idle and runs like crap.

Tonight was typical. I drove it 35 miles and it ran fine. I stopped and turned it off and the first time it started up, but the idle was rough. I shut it off again for about 5 minutes, and then it wouldn't start. The battery had plenty of cranking power, but it cranked and cranked and wouldn't start. When I pumped the accelerator, there was no smell of gasoline, so it wasn't like it was flooded.

I tried to start it a dozen times and it wouldn't fire. Finally, I called AAA for a tow, but when they arrived, the car reluctantly started up. I drove it home 35 miles, sweating all the way. The motor ran rough the whole way home, and when I had to stop for traffic lights or stop signs, again I got the loping (up and down) idle and had to gas it to keep it running.

I wrote in about this a couple of weeks ago and thought I had a bad tank of gas. I used Heet to get the water out and thought that would solve the problem. No such luck. I drove the car until it was down to about a quarter tank, then filled it with Chevron's highest octane gas. The problem persists.

Help!

 

Have you ever changed the injectors on the car? All 89 to 91's came w/ Mutlitech injectors that are problematic at best. I had many problems w/ my car that, in the end, turned out to be bad injectors. Check them FIRST, you need to ohm them cold and hot to get a true reading.
Do you have an FSM and a multimeter?

 

Thanks for the info. I don't have either an FSM (don't even know what that is) or a multimeter. I would probably have to have a mechanic check the injectors, but at $80 an hour ... might have to wait until the present Great Depression is over. Changing the injectors looks like a job for an expert, ergo, a huge expense. What injectors would you recommend if they need to be replaced? Thanks again.

 

My '90 had the exact same problems. I had water in the tank (bad gas cap). Mine was so bad that it fouled up my original multech injectors.
Got the Bosh III from Jon at FIC and car has never run better. Check out the "Sticky" at the top of this forum, Injector Videos and questions
Tons of info there

FSM = Factory Service Manual
Good luck

Jim

 

You could try having the injectors cleaned through the fuel rails. My 89 needed two cans of cleaner to get the injectors working properly.

FSM is factory shop manual.

 

Thanks again for your responses. I tried a fuel injector cleaner in the gas tank, but it doesn't seem to have helped. Also, I read in another thread that injector cleaner will damage the injectors. Maybe that is erroneous. Guess I'll try to figure out how to remove and clean or replace the injectors.

 

Do a search on Sam Lam, he is a member here that did a great writeup on how to change out your injectors. It outlines everythig you will need to complete the job, plus Jon at FIC is very helpful and a great resource if you get stuck on something. I would guess that you can complete the job for less then $300.00 if you do not have any tools.
BTW, post were you live, maybe someone here lives close by and can give you a hand.

Randy

 

I'm in Valley Springs, California, which is in the foothills of Mother Lode near towns like San Andreas and Jackson. Geez, I can't find that Sam Lam writeup on injectors. I guess I haven't got the hang of the search function. Does anyone have the URL of that article?

Anyway, I have an L98, and it looks like I have to remove the throttle cables and exhaust manifolds to get to the injectors. Is there a way of removing and installing the injectors without all that hassle? The factory service manual is no help at all.

Thanks again, everyone. If I can't do this project myself, it won't get done. A shop would charge several hundred dollars labor. I'm not an investment firm or a bank, so I can't get any government money to bail me out of this situation.

 

I'll sent it to you tomorrow, PM me your email address.

You really only need to remove the plenum, the runners stay were they are, you then take the fuel rail apart, and remove the old injectors. You will need new injectors and a "o" ring kit for the fuel rail and for were the fuel rail connects to the fuel lines to do the job. Good time to replace the ERG vavle, since the plemun will be off and you can install an adjustable fuel regulator too. Make sure the car has less then a half a tank of gas, as you need to disconnect the fuel lines.

Believe me, it is not that hard a job.

Randy

 

Fuel injector cleaner is one of the things that makes Multec injectors fail. It eats away the compound that seals the coil of the injectors and this shorts them out, the new fuels also eat it away so its a only going to get worse. Get new injectors because its only a matter of time until they stop working...WW

 

What shape are your plugs and wires in? Bad wires or plugs will cause the sputtering/loping idle problems you're experiencing, too.

If they're O.E.M. and you have more the 60,000 miles on the wires, they're likely played out and should be replaced. Be sure and replace the wire looms and holders, too. They get brittle from age and intense underhood engine temps and crack and dry rot in place.

 

Here you go:


Bob Lam’s article on injector removal
http://webpages.charter.net/buddiel/...al)%201-04.doc

Motorcraft fuel injectors
http://www.fuelinjector.citymaker.co...ge/5516057.htm
MotorCraft# Ford# Bosch# Borg Warner#
CM-4768 F4SE A1B 0280155700 57810

Injector flow data table
http://users.erols.com/srweiss/tableifc.htm

Injector flow rates
http://www.witchhunter.com/injectordata1.php4

1985-1993 Corvette, Camaro Pontiac T/A Bosch Design III upgrade Fuel Injector
http://fuelinjectorconnection.com/sh...&productId=134

Doug’s Dirty Dozen
http://www.lindertech.com/dirty_dzn.htm

TPI Injector Replacement
http://www.thirdgen.org/injectorswap

1997-2004 Fuel Injector Replacement
http://www.vetteweb.com/tech/vemp_07...ors/index.html

NOID light
http://www.drivewerks.com/catalog/Sh...AT447_pg28.htm

How to change your fuel injectors
http://www.corvettefever.com/howto/c...uel/index.html

Understanding Fuel Injector Wave Forms
http://www.automotivetestsolutions.c...rWaveforms.htm

Intake Plenum Gasket
http://www.autozone.com/R,APP1104544...ductDetail.htm

Fuel rail seal kit
http://www.autozone.com/R,APP1136249...ductDetail.htm

Valve Cover Gasket
http://www.autozone.com/R,APP673059/...ductDetail.htm


Regarding Injector Testing:

1990 Corvette 5.7L (VIN8 – L98) Completely Stock

Problem:
When it is cold, the engine consistently starts and runs reliably. After the engine comes up to operating temperature, when it is shut off, it will not start; it cranks but will not run.

Diagnostic Tests:
Following diagnostic chart A3 in the FSM
• No codes are present
• Good spark is present on all cylinders
• When the engine is cold, a noid light blinks reliably on cylinder 1; when the engine is hot, it will not blink
• When the engine is cold, a noid light blinks reliably on cylinder 2; when the engine is hot, it will not blink
• When the engine is hot, disconnecting the cylinder 2 injector will allow the engine to start; reconnecting it while the engine is running will cause the engine to stop running

Injector Resistance:
Cy- Cold - Hot
1 - 16.7 - 17.3
2 - 06.4 - 00.7
3 - 12.6 - 08.9
4 - 16.1 - 15.1
5 - 16.8 - 17.6
6 - 15.5 - 12.2
7 - 15.6 - 12.1
8 - 16.1 - 16.9

Conclusion:
Injector #2 shorts out completely when it is hot. When cold at 6.4 ohms, it will alllow the engine to start and run.

By the Way:

I cured a loping idle in my '90 by cleaning the Throttle Body and IAC; I now do it as routine maintenance once every other year.

.

 

Thanks, Randy!

 

I believe the original injectors are still on the car, so no doubt they need replacing after 18 years.

 

The plugs and wires were replaced shortly before I bought the car, so they only have a few thousand miles on them. However, I haven't looked at the plugs so I guess I'd better pull those, too, to see how they look. Thanks!

 

Wow! Thanks for taking time to send all these links and info. I'll clean the throttle body and IAC while I'm at it. I guess I should check the fuel filter, too?

 

This may be the case for some however the vehicle in question,
1989, has logged another 30K since the injectors were cleaned through the fuel rails, 140K total, & it still has the original injectors. So for me the jury is still out.