Kleantouch

Hi all, Brand new to this forum- Have had my 90 vette for about 3 years now- black conv 6 spd, 58000 miles- The othr day I drove it about 10 miles, ran great- shut off, tried to start after sittting for aout 3 hours- started fine, would not accelerate, any movement with gas pedal would cause engine to sputter, could not drive it- So I left it overnite- next morning started right up and drove it home with NO problems- Next weekend started right up, accelerated out the garage, got about a mile, stalled- then would start, but would not accelerate- Started next morning, got it home fine- No SES Lights, no blinking, no over temps, oil good, etc.

Haven't pulled any codes, or even tried yet. Just wondering if this is common- my 71 454 Blazer doesn't have all the electronic bells and whistles.

Any help would be most appreciated!
Thanks,
and I'm glad I found you guys.

89vettefromhell

FUELLLLLL PUMP... just had the same thing with my 89... check your Fuel pump relay and the fuel pump... also .. make sure your battery is good and the connectors... i would suggest getting now bolts if your battery is side mount inserts... and CLEAN THE **** out of the contacts that connect to the battery... make sure theres no acid or corrosion on them... im 99.9% sure its your pump though... as this happend to me 2 weeks back .. i replaced the pump and bam.. back to new!

Kleantouch

Thanks for the info and confidence- duplicated the discrepancy in the garage- ran good then bogged down, etc. No codes except 12 when jumper a-b.

HOw hard was it to change the pump- looks pretty straightforward in the book???

Thanks again.

Carl

AGENT 86

Before you throw money at a new pump i would verify that it is the pump. Do you have a gauge you can attatch to the shraeder valve on the fuel rail ? Taping it onto the windshield will allow you to drive it and monitor fuel pressure under load.

Kleantouch

Thanks for that piece of advice- First- I spent some money and replaced the fuel pump.-- NO JOY! And a fuel filter as well.

And since I can't get the motor to stay lit while I put it in gear, I can't drive it. NO codes

Any other thoughts?
Thanks,
CArl

AGENT 86

I would still check to see what your fuel pressure is and are the injectors being fired.
I reread your posts as i didn't absorb everything (red wine factor)
I gather that it idles now but dies when you put it in gear. Is this when warm only ? Have you checked your spark plugs (fouled)? Are all of them providing spark ?
Do you have access to a scanner or laptop with software ?

Kleantouch

Thanks, Agent 86- I understand the red wine factor-
When cold, engine runs, accelerates, gets good RPMs, when it warms up, no acceleration, if it does accelerate, it immediately drops rpms.

Yes I have laptop, but no scanner/scan tool.

Carl

AGENT 86

Well it sounds like it runs good in open loop and and like crap in closed loop. The O2 sensor is ignored in open loop so it could be a faulty O2 sensor. Food for thought

tjwong

When you attempt to rev the engine does it sound different? Perhaps the CAT is broken up and packing up when its hot causing a restriction in the exhaust. If its a clogged exhaust you can test it by removing the AIR fittings on the exhaust manifolds and try to drive it. It will be noisey but if the problem is a clogged CAT the performance should improve by allowing exhaust flow through the fittings at the manifold.

Another problem can be the ignition system if its missing after its hot. Check the distributor, check the pole peice inside the distributor, disconnect the two wire connector and use an ohm meter to check for continuity across the connector. It should read around 1000 ohms. Remove the coil and check for any carbon tracking in the cap area. Also make sure that the internal ground strap under the coil is there and making a good connection

89vettefromhell

did you also check the pump relay.. and wires.. alot of time its not the fuel pump only ... your wires are corroded or something from the years of wear and tear.. im telling you this is your fuel system somehow... mine did the EXACCCCCT same thing... also check and make sure your battery is making good connection to the connectors.. and try cleaning the contact points on them.. and did you put the pump in yourself ... if so double check that the pump is in the fuel pulser Tightly



edit: on another note... whens the last time you had a tune up... make sure all your connections to your sparks are good... could be getting a misfiring cylinder

Vette73

Because it's a '90, and you get no codes, I'm going to bet that it is an injector shorting out -- common on '89 and '90 L98s. Look at your injectors: are they light and dark gray, or gray and silver? If two shades of gray they are the originals which could be replaced under a 1991 TSB -- if they failed. Your car may have a mix of injectors if one or some were replaced earlier in life. The problem you describe is textbook. The injectors heat up and then short out. When they cool off, they work again until they heat up. The problem will only get worse until one shorts completely. Since the injectors are in series per side, when one shorts, it overloads the other three on that side and kills them too. You can test the resistance of the injectors (hot in this case) and just replace the "bad" one, but as they say, "tear down time is the same for one or eight". It's up to your budget.

Kleantouch

Thanks, Vette73. The injectors are gray and silver- all look alike- I'll read up on ohmic values and warm the beast up until it runs rough and then ohm the injectors. And if that turns out to be the case, I'll replace them all. I've noticed quite a discussion in other threads about injectors, so I won';t ask your opinion- well, pm me if you want to weigh in on injectors.

I did get under the car and bang on the catalytic converter- my muffler guy said if it rattles- like rocks loose inside, the cat is fried and it needs to be replaced. No rocks from what I could tell.

Thanks, and I really appreciate all the help.
I'll keep everybody posted.

Carl

Morley

Coolant temp sensor, causes exactly what you describe. Runs good in open loop, runs like crap closed and gets worse as the engine gets warmer... $7 at Advance auto.

Vette73

Maybe...

You can test (and rule out) the coolant temp sensor like this:

On the C68 A/C controller, press and hold the up and down fan buttons simultaniously for about four seconds with engine running. The display will show 00. Use the up fan button to scroll to 16, then press the auto-fan button. The display shows the engine temp (in degrees C) being read by the coolant temp sensor. You actually have two sensors on the '90 L98: one for the gauge (right side of block) and one which the ECM (and the C68 module) uses (front of intake below the TB). If the display temp on the C68 and the gauge temp (which is only approximate) are close, the sensor the engine control module uses is good and can be ruled out as the cause of your problem.

Good luck.

johnzz4

MAF can cause this as well.... simple test too... disconnect it when it's sputtering and see if the condition improves. This likely isn't the culprit because of the 'hot only' problem, but it's such an easy test, it's worth trying.

skateparkdave

90 is a speed density car = No MAF. Uses MAP instead.
As long as you have steady fuel pressure and a good fuel filter then my $ is on CTS, O2 sensor or injectors. All will yeild simular troubles. CTS is the most likely of them to cause troubles without throwing a code and could explain why it runs good until warm because the ECM uses CTS to adjust values after car is warm.

Kleantouch

Looks like we have a winner- the injectors- Ohmed them out cold, all but 1 in the 16-18 ohm range- # 5 ohmed about 12 ohms. Started itup, warmed it up, got the stuttering/loss of power. Shut down, ohmed out the injectors again, all 16-18 ohms except 5, now down to 2 ohms. JUst for grins I left #5 unplugged- fired right up, lots of power! Plugged 5 back in, back to stuttering/loss of power. Looks like shopping trip to 5-0 motorsports- they seem to have the best pricies on Bosch 22# injectors!

Maybe I'll also flush the rad, tune it up and change the plug wires.

Any comments on changing injectors (I know a lot has been posted already and I will research it while I'm waiting for parts) and/or use of gasket cement for the air plenum?

Thanks again!

Happy 4th of July!

Semper Fi!

moose1990

I had the same problem last year. Replacing the ecm cured mine.

Kleantouch

Just an update- bought 8 new injectors from Five O motorsports- GREAT PRICE, SERVICE, ETC. Thanks Bruce.

Lots of great tech tips on this forum- made the job SOOO much easier.

Started up, warmed up, no problems.

Only one thing to say besides THANKS- VRRRROOOOOOOOMMMMMM!

AGENT 86

to Bruce once again
I bought the pink tops