1991 l98 vette engine trouble.
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1991 l98 vette engine trouble.
i recently bought a 1991 auto with the l98 tpi engine. when i got it, it was running bad, so when i got it home i checked the plug wires, made 1 new one, and fixed the problem. ran great for about 4 miles, when i decided to hammer down and blow the dust out of it. well, it ran great until i let off, then started missing again, worse than before. at this point it would barely idle. I replaced the plugs, replaced all the wires with new oem 8mm wires, replaced the cap and rotor. Seamed to be a little better, but when i test drove it, it felt like it was still running on 4 cylinders.Upon tearing into it, i noticed when you turn the key on, the fuel pump runs continuously, instead of for 2 secs like factory. then i found a jumper wire going from fuse box to fuel pump. apparently there is a relay problem or something. next i made a fuel press test gauge from some old a/c hoses. it has 39 at idle, and 45 at wot. next i put a scanner on it, all sensors seam to be working fine according to the readings from the scanner, and info from my tpi tuning book. FIRST, what do you guys think could be wrong, and SECOND, where is the fuel pump relay at? thanks.
Le Mans Master
Joined: Feb 2006
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From: Louisiana
Not sure if a 91 is the same, but on my 86 the fuel pump relay is located on the driverside of the windshield wiper motor on the firewall. Have you check fuel pressure after shutting down the engine for leaks? Have you ohmed the injectors hot and cold?
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From: The Top of Utah
The fuel pump relay is on the firewall near the ww motor. Based on the fuel pressure you report, neither the relay nor the fuel pressure are causing the drivablity problems. But the wiring to the relay needs to be corrected. With your new car, you are going to need a FSM (Factory Service Manual) to learn exactly how each system works and for the trouble shooting charts you won't find in a generic repair manual.
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relay
ive seen pics of the relay where you are descibing in my haynes manual, but my car doesn't have one there. it does have a row of 5 relays hanging from under the pass. side dash near the fuse panel.could it be one of these? also it has 2 relays mounted on the drivers side of the radiator, i assumed they are for the fans? thanks for your input.
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From: The Top of Utah
Originally Posted by jimmya
ive seen pics of the relay where you are descibing in my haynes manual, but my car doesn't have one there. it does have a row of 5 relays hanging from under the pass. side dash near the fuse panel.could it be one of these?
Originally Posted by jimmya
also it has 2 relays mounted on the drivers side of the radiator, i assumed they are for the fans? thanks for your input.
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info
im a nitrous/carb drag racer, but new to the fuel injected corvette. any info on engine/exhaust, etc. would be appreciated. im thinking on building a 377 with mini-ram and 58mm tb, true dual 3 " ex with no cats, and egr/smog crap deleted. any problems with this? (no legal issues, i live in arkansas!).
Pro
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From: Charlotte MI
Originally Posted by jimmya
im a nitrous/carb drag racer, but new to the fuel injected corvette. any info on engine/exhaust, etc. would be appreciated. im thinking on building a 377 with mini-ram and 58mm tb, true dual 3 " ex with no cats, and egr/smog crap deleted. any problems with this? (no legal issues, i live in arkansas!).
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Melting Slicks
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From: St. Charles, MO Route 66 Corvette Club
jimmya: As RRTVette suggested, check the resistance of each fuel injector. The ohms should be between 16 and 17 ohms......and all eight injectors should be very close to the same reading both hot and cold. If you find injectors below 16, they are shorting out and this MAY be your problem. Very easy to check and rule it in.....or out!
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I just ohmed my injectors on my ´91 after i read this, and found that 5 are over 17 ohm, 1 is at 13,9 and 2 are at 6,2 or so. No wonder mine goes like an audi. Are they easy to change and what is the best type to buy? Thanks for any reply...
Le Mans Master
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From: The Motor City
Originally Posted by jimmya
. it does have a row of 5 relays hanging from under the pass. side dash near the fuse panel.could it be one of these?
The other 2 by the rad. shroud are for the fans.
I would first get the electrical straightened out (as CFI originally suggested), ie. eliminate whatever jumper wires that should not be there and fix the problem.
Yes the FSM would help, I would also get the electrical volume.
Last edited by mseven; Sep 21, 2006 at 07:43 AM.
Le Mans Master
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From: Louisiana
Originally Posted by vette079
I just ohmed my injectors on my ´91 after i read this, and found that 5 are over 17 ohm, 1 is at 13,9 and 2 are at 6,2 or so. No wonder mine goes like an audi. Are they easy to change and what is the best type to buy? Thanks for any reply...
Melting Slicks
Joined: Apr 2002
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From: St. Charles, MO Route 66 Corvette Club
Originally Posted by vette079
I just ohmed my injectors on my ´91 after i read this, and found that 5 are over 17 ohm, 1 is at 13,9 and 2 are at 6,2 or so. No wonder mine goes like an audi. Are they easy to change and what is the best type to buy? Thanks for any reply...
Hi Bob,
The problem you currently have is that from 1989 through 1991 on the L98 engines GM installed Multec injectors. These injectors have one of the highest failure rates of any injector ever installed. It's not a matter of "if" they are going to fail, it's simply a matter of "when" they will fail. That is why some of your injectors look differently than the others. Some of them have obviously already failed and were replaced. Because of their design they cannot be repaired so the only solution is to replace them.
You can try to find some of the same injectors to use as replacements however they will likely eventually fail also so a better alternative is to replace them with an aftermarket set of replacement injectors or find some of the earlier Rochester injectors that were used from 1986 though 1988 on the L98's. These were a Bosch design injector and they don't have the problems that the Multecs do.
I don't sell any injectors so I can't help with supplying replacements but if you do find a set of the earlier design injectors I can service those and they have a very good track record of long life and serviceability. The part numbers you would be looking for are: 1986 = 5235211, 1987 and 1988 = 5235302. These are the part numbers that are on the injectors themselves. They are not the part numbers that would be listed in a GM parts catalog.
Sorry to be the bearer of bad news but that's just the way the Multec injectors are.
Hope this helps. Let me know if you need more info or have additional questions.
Rich Jensen
The injectors can be removed and reinstalled with 4-5 hours of your labor. The injecor removal time is reduced if you do not remove the runners from the intake manifold. The project requires some tools and in not a difficult job. If you want details on this, send me a note to samlam@charter.net
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comp check
i had a feeling it was a mechanical problem, so i did a compression check. all 185-200psi, so i guess thats good news. moving on to injector check i guess. do you ohm them out from left wire to right wire unhooked, with the engine off, i presume?
Le Mans Master
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From: Louisiana
Originally Posted by jimmya
i had a feeling it was a mechanical problem, so i did a compression check. all 185-200psi, so i guess thats good news. moving on to injector check i guess. do you ohm them out from left wire to right wire unhooked, with the engine off, i presume?
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test.
ok. the injectors all test good. when i ohm out the left wire in each harness, the drivers side all have continuity and the pass side injector harnesses have none. any ideas other than the obvious bad wire?
Melting Slicks
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From: St. Charles, MO Route 66 Corvette Club
Originally Posted by jimmya
ok. the injectors all test good.