1990 C4 having issues....Help
Thread Starter
Cruising
Joined: Oct 2016
Posts: 11
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From: Lexington Alabama
1990 C4 having issues....Help
I have a 1990 L98 Corvette all stock....it will crank but as soon as u touch the gas it starts sucking air and dies. It began as an intermittent problem while driving down the road. Now it won't even leave the drive way. I replaced the TPS and MAP sensors and the fuel filter....idk where to look now....no codes are showing except the 33 and 34 and i have seen 3 explanations for those codes...any ideas would be a amazing...I greatly appreciate it..
Nicklas
Nicklas
Last edited by Nixster1992; Oct 27, 2016 at 06:27 PM.
Team Owner
Joined: Jul 2004
Posts: 28,470
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From: Hartford WI
I assume you have air so lets go with fuel and spark. When it does this, disconnect the plug wire from the plug and hook it to a known good plug and ground the threads. Better yet, use a spark tester. You should get a blue flame. If you do, make sure the timing is right. Also check fuel pressure to see what it is at idle and when you pull off the FPR hose and then how long it takes to bleed down.
Thread Starter
Cruising
Joined: Oct 2016
Posts: 11
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From: Lexington Alabama
Fuel pressure is good...around 45 psi.... already tested it...I will check the spark to see if it's getting the right spark...and I don't have a timing light...could the coil pack be going bad or other sensors that could be fouling without throwing a code???
Team Owner
Joined: Jul 2004
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From: Hartford WI
If you are not going to get a blue flame it may be weak .
Team Owner
Joined: Jul 2004
Posts: 28,470
Likes: 3,289
From: Hartford WI
Beg, borrow or steal as my grade school teacher used to say when we forget to bring required supplies
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Thread Starter
Cruising
Joined: Oct 2016
Posts: 11
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From: Lexington Alabama
The one thing I know for sure is I put a catalytic converter back on the car and it began 3 days after...I'm not sure if it's related...it was an off the shelf universal magniflow...
Team Owner
Joined: Jul 2004
Posts: 28,470
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From: Hartford WI
I have serious doubts it made that much of a difference. How did you determine the 10 degree difference? That is pretty slight and the gauges aren't the greatest.
Instructor
Joined: Dec 2014
Posts: 144
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I had similar issues with my 91. Ended up being one of the original 3 cats was collapsed and another was clogged. Replaced the original system with a single high flow cat convertor, no issues since. How old is your O2 sensor?? Also check your sock filter on the fuel pump.
Racer
Joined: May 2004
Posts: 411
Likes: 1
From: New Hampshire
I had identical problem as woody41 with my 90. Collapsed original cat....Mine would idle but once I tried to accelerate....stall. I touched the pipes after the cats on the front pipe after idling and could tell huge temperature difference...right side was ice cold. I disconnected and lowered the front pipe from the manifolds to test it... started car (very loud) and accelerated....no stalling. Had to replace font pipe. replaced center cat too while I was at it.
Of course had to get screwed by the CA CARB requirement here in the occupied territory of the people's party of the Republik...
Of course had to get screwed by the CA CARB requirement here in the occupied territory of the people's party of the Republik...
Last edited by Streamline; Oct 28, 2016 at 11:09 AM.
Team Owner
Joined: Jul 2004
Posts: 28,470
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From: Hartford WI
I had identical problem as woody41 with my 90. Collapsed original cat....Mine would idle but once I tried to accelerate....stall. I touched the pipes after the cats on the front pipe after idling and could tell huge temperature difference...right side was ice cold.
I disconnected and lowered the front pipe from the manifolds to test it... started car (very loud) and accelerated....no stalling. Had to replace font pipe. replaced center cat too while I was at it.
Of course had to get screwed by the CA CARB requirement here in the occupied territory of the people's party of the Republik...
I disconnected and lowered the front pipe from the manifolds to test it... started car (very loud) and accelerated....no stalling. Had to replace font pipe. replaced center cat too while I was at it.
Of course had to get screwed by the CA CARB requirement here in the occupied territory of the people's party of the Republik...
That is an excellent way to do it. I have done that for testing of the cat back exhaust and found little to no difference with or without the Borlas hooked up.
Kinda why I would never move there or go there for more than a visit
Instructor
Joined: Feb 2013
Posts: 193
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From: Evansville IN
Fuel injectors.
Check the fuel injectors. If one fails the car won't hardly run at all. Unplug them one at a time. When you find the bad one it'll smooth right out. I just went thru what sounds like the same thing you're going thru. What a mess it was to figure out. Good luck.
You have some stones to touch the cat. I don't have the guts to touch anything I think is hot unless it is a hot girl. I have an infra red thermometer for that.
That is an excellent way to do it. I have done that for testing of the cat back exhaust and found little to no difference with or without the Borlas hooked up.
Kinda why I would never move there or go there for more than a visit
That is an excellent way to do it. I have done that for testing of the cat back exhaust and found little to no difference with or without the Borlas hooked up.
Kinda why I would never move there or go there for more than a visit
Thread Starter
Cruising
Joined: Oct 2016
Posts: 11
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From: Lexington Alabama
Ok new coil pack and ignition control module. It will now idol better but still dies if u try to press the gas to fast...I got it to rev to 3000 before it tried to die....still at a loss...so new tps, map, computer, coil pack, and ICM....still messing up....any ideas???
Team Owner
Joined: Jul 2004
Posts: 28,470
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From: Hartford WI
Ok new coil pack and ignition control module. It will now idol better but still dies if u try to press the gas to fast...I got it to rev to 3000 before it tried to die....still at a loss...so new tps, map, computer, coil pack, and ICM....still messing up....any ideas???
Racer
Joined: Mar 2013
Posts: 462
Likes: 98
If you get good fuel pressure with the car running, what happens when you turn the motor off? If the fuel pressure immediately drops, you either have a bad fuel pump, a bad regulator, or as in my case, at least one injector is leaking fuel at all times.
New fuel injectors (I went with the OEMs) , pump and gas filter did the trick for me.
New fuel injectors (I went with the OEMs) , pump and gas filter did the trick for me.
Advanced
Joined: Aug 2016
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Ok new coil pack and ignition control module. It will now idol better but still dies if u try to press the gas to fast...I got it to rev to 3000 before it tried to die....still at a loss...so new tps, map, computer, coil pack, and ICM....still messing up....any ideas???
Instructor
Joined: Feb 2008
Posts: 177
Likes: 5
From: Toronto Ontario
Take a real close look at all your vacuum hoses for splits or bad connections. A vacuum leak to the MAP sensor can cause all kinds of drivability issues. Don't overlook items that use a vacuum source such as the brake booster and the cruise control.
Racer
Joined: Mar 2013
Posts: 462
Likes: 98
I would not keep changing parts out, as that gets expensive and you are likely replacing things that are not broken to begin with.
Honestly, if the car runs and if you push down the accelerator and the car dies, it sounds like a fuel feed problem. The inrush of air is leaning the mixture to the point it won't ignite. Could be a lot of things, but I'd focus on fuel pressure first (assuming the vacuum test shows around 20 steadily), around 43 psi with the car running, and even if you rev it a bit. If the pressure is not right, bingo. And if the fuel pressure drops to zero immediately on shutting off the car, you've found the problem. And then have to determine if it is a leaking injector(s) bad fuel regulator or a fuel pump with a bad check valve.
By the way, and you may already know this, there is a vacuum line that goes to the fuel pressure regulator. Good to check that is there and in good condition.