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I have a '91 convertible that I drive only in the summer with about 16,000 miles on it. I bought it used when it was a year old, so it is mostly original. The fuel pump went last week and the car died and wouldn't start, which was bummer. I replaced the fuel pump, fuel filter, screen, sending unit all was pretty easy to do; then started it and it idled pretty rough and knocked on very low idle. So then, I then did a complete tune up with new dist cap, rotor, plugs and wires, but reused the old coil. But that didn't make much difference, it still idles rough. So now I'm scratching my head. The problem apprears fuel related, so is it possible that I need new fuel injectors? Or can it be something else? So before I go out and buy new injectors any advice will be appreciated. Here are a couple of photos of my car:
I’d think injectors. Ohm them out and post your results.
Do you have a fuel pressure tester?
are you sure the fuel pump was bad?
keep your oem parts you replaced. Chances are they are better than the stuff you put on.
I have a multi-meter so I'll check each injector. I'm guessing the ohm should be between 15 - 17, but that is just a guess.
I do not have a fuel pressure tester, but can borrow one. I can't be 100% sure the fuel pump was bad, I tried for hours over a few days to start the car. Sprayed starting fluid a bunch of times but it wouldn't run; but when I replaced the fuel pump the car fired right up. Coincidence? Maybe, but at least the car is running, although, at low idle it hestitates. It sucks not having the right diagnostic tools. Mostly diagnosing by the seat of my pants. You are right about the OEM parts, most of the replacement parts seem to be made in China.
If it turns out to be the injectors, any recomendations on which brand to buy? I already looked online and the prices are all over the place from $40 to $120 per injector.
Oh and that car is beautiful. You don’t see many unmolested C4s anymore.
Thanks, I've had the car for 29 years and maybe had the top up 5 times. The top does have a one inch crack in it and was planning to replace the top, but figured why bother since I'd probably never use it. The guy I bought the car from had an after market alarm installed but I disconnected and removed most of it, so the only thing not orginal to the car is a piece of plastic trim that fits in between the power seat switches where they drilled a hole an put in a small red lense/light. I'd like to replace it but haven't been able to find a replacement part. I assume it snaps off and a new can be snapped on. See photo below:
I’d think injectors. Ohm them out and post your results.
Do you have a fuel pressure tester?
are you sure the fuel pump was bad?
keep your oem parts you replaced. Chances are they are better than the stuff you put on.
Just finished resistance testing the injectors. Here is what I got:
Driver's side fire wall to fan: 15.0 16.5 16.4 16.5
Pass side Fire wall to fan: 5.1 16.5 16.2 16.5
So it looks like one injector is bad and one is borderline. So that explains some of the symptoms.
Now my questions are:
1. Should I replace the Idle Air Control valve while I have the plenum and fuel rails off?
2. What brand injectors would you recommend?
Thanks, Dave D
Beautiful car! I replaced 'everything' under the plenum but with the very low miles not sure replacing parts such as the IAC makes sense. Since you did have the fuel pump go out maybe replace the fuel pressure regulator too?
I used drop-in Bosch III's (I think..) from FIC, rebuilt and matched.
This could be wrong info, but those multec injectors can ohm out okay but still be failed due to the ethanol ruining the seals inside the injector.
I know some go through fuel injector connection for new ones.
since your car is so close to OEM, I’d personally spend the coin and put new multecs in it.
You raise an excellent point. I don't mind spending a little more to get quality parts, and I have been trying to keep the car as close to original as possible. Not for resale reasons, but It just seems like more fun for me to look at it and think that's how she left Bowling Green.
I figure while I have it apart I'll clean the inside of the fuel rails and throttle body.
Beautiful car! I replaced 'everything' under the plenum but with the very low miles not sure replacing parts such as the IAC makes sense. Since you did have the fuel pump go out maybe replace the fuel pressure regulator too?
I used drop-in Bosch III's (I think..) from FIC, rebuilt and matched.
Good suggestions, I'm going take advantage of having it apart, take my time and see if i can get it purring like a kitten. Pretty much everything under the hood is 30 years old. My other Corvette is a '71 and for me, tuning it, adjusting the carburator and getting it running smoothly is so much easier. Thank you for your advice.
'91 Rough Idle?
