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| jwardg | 90 C4 performance degrades the longer it runs | ||
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Its a 1990 convertible. I bought the car about 18 months ago and have done a series of tune up related repairs on it. Brake system overhaul, cat-back exhaust, plugs, wires, serpentine belt, etc. Overall, Id say, for its age, it runs pretty good....for the first 15 to 20 minutes.
Then it steadily, progressively runs worst. As if to lose power, poor acceleration, skipping, missing, struggling. On my last drive, it ran for a while, then when climbing a small hill, it shut off. Not sure which way to go with this one. Anyone seen this symptom? Thanks . jwardg |
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Posted on: 2011/2/9 19:49
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| bogus | Re: 90 C4 performance degrades the longer it runs | ||
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First off, welcome to the Guru!
 This sounds like a classic example of a fuel pump failing. As they warm up, they just can't pump anymore. I would put a fuel pressure gauge on it and see what happens. |
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Posted on: 2011/2/9 20:04
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| TommyT-Bone | Re: 90 C4 performance degrades the longer it runs | ||
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Chair-man of the bored
 
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Ohm the injectors while your at it.
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Posted on: 2011/2/9 20:11
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| josephf31 | Re: 90 C4 performance degrades the longer it runs | ||
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I agree, my '91 has pretty much the exact same issue, I changed the injectors quite some time ago, things were good then the distance/time I could go before it felt like running out of fuel became less and less. Haven't replaced the fuel pump yet but it's in my top 3 "to dos" for the spring :-) |
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Posted on: 2011/2/9 20:32
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| Ultraman | Re: 90 C4 performance degrades the longer it runs | ||
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Welcome to Guru! You will want to replace the fuel filter unless you have already done that when you put in a new fp.
Post some pics of your 90. What color is it? |
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Posted on: 2011/2/9 20:49
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| 62panshovel | Re: 90 C4 performance degrades the longer it runs | ||
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My injectors acted this way when failing. Ran great cold. Dont know how though. Good thread here with lots of info.
http://forums.corvetteforum.com/c4-te ... videos-and-questions.html I am not trying to push CF by any means BTW... |
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Posted on: 2011/2/9 22:12
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| Matatk | Re: 90 C4 performance degrades the longer it runs | ||
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First thing I'd check is fuel pressure. Do you have a gauge? If not, you can get one at Harbor Freight or parts stores for around $40 give or take. You'll hook that up to the valve on the passenger side fuel rail. Monitor it while you are having the symptoms. Also ohm the injectors as mentioned by Tommy, the multecs from that generation have a habit of the coils shorting out with age and ethanol added fuel. If neither of those are the issue, we need to start tracing electrical problems. But I bet it's fuel pressure related
 Matthew |
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Posted on: 2011/2/9 22:30
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2002 EBM convertible, Magnusson supercharger, cam, headers, etc. 1989 Corvette...RIP |
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| RickAnthony | Re: 90 C4 performance degrades the longer it runs | ||
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I agree.. check the fuel pressure see if it is slowly dropping as the performance drops. Did it die and restart right away? Or did you have to crank it a bit before it fired up? Many items fail like this when they heat they start to drop out.. see this with ignition components alot.. but the fuel pump would be top of my list for sure.. injectors could be an issue as well... but there are 8 of those to fail, and it would have to be more then one failing I think to cause it to die out.. but I'm not ruleing it out... |
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Posted on: 2011/2/10 5:54
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| TommyT-Bone | Re: 90 C4 performance degrades the longer it runs | ||
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Chair-man of the bored
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I had that type of issue a few years ago. The EGR valve had failed, my fuel filter was old, I had some spark plug wires that were arcing, replaced the exhaust system and a bank of injectors had failed. Not sure if we replaced the fuel pump too but it's possible. It could be one thing or it could be a combination of things. That was all for my 90 also. Today it runs like a champ. I'll be watching this thread for updates. I'd really like to know what you find.
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Posted on: 2011/2/10 11:45
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| josephf31 | Re: 90 C4 performance degrades the longer it runs | ||
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As mentioned, my '91 developed the same problem not long ago. It has a new EGR, fuel filter, injectors and spark plug wires, process of elimination (and posts like this) tell me it's the fuel pump, but I won't know until the snow and ice are gone and the temperature rises above single digits so I can work on it; also keeping an eye on this thread though, thanks... Joe |
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Posted on: 2011/2/10 16:31
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| jwardg | Re: 90 C4 performance degrades the longer it runs | ||
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Thanks to all for your helpful input. Life came calling and Im just now getting back on the car. Since my initial post, the fuel pump, relay, ECM, fuel filter and one injector have been replaced. Car still runs for about 30 min, starts to skip a bit and then shuts off.
Ive ohm checked the injectors. Got readings ranging from 16.3 to 4.9. Pulled the fuel sending unit out, wiped the tank clean and noticed the strainer had little debri but had a small tear. Id like to replace the torn strainer, but when I tried, it wouldnt come off, a least not with mild force.Ive decided to tackle replacing the injectors and the strainer. Any tips to a corvette newb in trying this job of replacing the injectors? and the strainer without damaging the fuel pump and sending unit? Thanks in advance for your input. |
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Posted on: 2011/10/18 22:17
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| josephf31 | Re: 90 C4 performance degrades the longer it runs | ||
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That range of injector resistance is not good, probably should replace them; check out the vendor forums and past posts for Jon @ FIC for the best injectors and deal.
The strainer on the fuel pump pickup is just a press fit of the metal cap to the bottom, it may take a little coercing but then it should pop right off. Update on my issue; replacement fuel pump etc. resolved my issue, seems to be running really good now. |
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Posted on: 2011/10/18 22:28
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| Ultraman | Re: 90 C4 performance degrades the longer it runs | ||
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Does it start right back up after it shuts off or does it stumble around running rough, or not start for awhile?
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Posted on: 2011/10/18 23:13
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| RickAnthony | Re: 90 C4 performance degrades the longer it runs | ||
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Sounds like possibly an injector is shorting after it warms up....
The L98 is "gang-fired" maybe one injector is shorting and causing the others to be cut off when this happens maybe causing it to stall? So sounds like your on the right track.. |
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Posted on: 2011/10/19 0:20
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| Matatk | Re: 90 C4 performance degrades the longer it runs | ||
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Welcome back. The injectors should be replaced...all 8 of them. I have a write up in the tech library.
As far as the filter sock, it's just a compression fit. It probably got stuck on there with age, perhaps some corrosion. Try to gently wiggle it back and forth with some channel locks. Matthew |
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Posted on: 2011/10/23 3:26
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2002 EBM convertible, Magnusson supercharger, cam, headers, etc. 1989 Corvette...RIP |
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| jwardg | Re: 90 C4 performance degrades the longer it runs | ||
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Guru Newb
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Thanks for the info.
Does it start right back up? No. Once it gets warm and shuts off, it won't start back up at all for a while. So Im now knee deep into the job of replacing the injectors. PIA, trying to get to the lower torx screws on the right and left intake runners. Looks like this may require either a special torx tool or removal of the valve covers. This may be a deal breaker. Is there a way to remove the fuel rail assy without removing the intake runners? |
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Posted on: 2011/11/1 4:05
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| Matatk | Re: 90 C4 performance degrades the longer it runs | ||
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It is possible to remove the rails without removing the runner but is a lot of work. Read my write up in the tech library. It's easier to remove the runner. Your best bet is to use the roof ratchet on an extension, a wobble might help too. I got a snap on long shank torx bit when I did mine, helped a lot.
Matthew |
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Posted on: 2011/11/2 0:20
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2002 EBM convertible, Magnusson supercharger, cam, headers, etc. 1989 Corvette...RIP |
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| jwardg | Re: 90 C4 performance degrades the longer it runs | ||
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Thanks Matatk,
Well, I got creative and after several trips to the hw store I finally came up with a contraption that works to remove the lower torx screws. A 12 in, slim extention and a wobble and t40 torx bit. The right runner came off ok, the left one is a B. I got the left runner to move just enough for me to get the fuel rail out, but something is holding it in although the torx screws are removed. Back to the grinding stone... Did you replace the EGR valve or thermostat while you had things disassembled? |
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Posted on: 2011/11/2 13:25
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| Woodstock | Re: 90 C4 performance degrades the longer it runs | ||
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but something is holding it in although the torx screws are removed There are 2 screws from the inside, one on each side. Left is in the rear part, covered by the distributor. Right is in front, covered by the egr solenoid. |
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Posted on: 2011/11/2 17:10
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| Matatk | Re: 90 C4 performance degrades the longer it runs | ||
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Like Axel said, there are two "hidden" torx bolts.
I don't see a reason to replace the EGR if it's functioning. You will fall into the "while I'm in there" black hole and replace tons of stuff. Vacuum lines that are brittle/cracked should be replaced. Now is a good time to do the throttle body coolant bypass. It will make things easier in the future if you have to remove the TB or do work around there. You also might consider changing the torx head bolts to allen caps. There are kits on ebay, or if you have a good enough hardware store you might be able to piece a kit together. I hate those torx heads. Matthew |
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Posted on: 2011/11/3 1:30
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2002 EBM convertible, Magnusson supercharger, cam, headers, etc. 1989 Corvette...RIP |
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| jonszr1 | Re: 90 C4 performance degrades the longer it runs | ||
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Senior Guru
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this is just a thought ,but you might ck the coil.coils can start to go bad when they get hot .
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Posted on: 2011/11/3 2:38
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| jwardg | Re: 90 C4 performance degrades the longer it runs | ||
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Thanks to all for the info. Well I got the runners off, replaced all the injectors. It runs better now and doesn't cut off when it gets warm. It still smells a bit rich from the exhaust. The car has falied emissions inspection twice.
I plan to run it everyday for a while to see if clears thing up. |
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Posted on: 2011/11/10 4:45
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| Matatk | Re: 90 C4 performance degrades the longer it runs | ||
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Did you pull the battery cable and turn on the headlight switch? That removes any residual power. You have to reset the ECM for your fuel tables since the old injectors probably made it all out of spec trying to adjust.
Also, have you replaced the O2 sensor? One wire sensors are a maintenance issue...they should be replaced at like 30-40,000 miles. That will also make a difference with how it runs. Go to rockauto.com, they have the best prices. Get a Denso/NGK sensor. Matthew |
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Posted on: 2011/11/10 12:30
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