LT1 Based Engine Tech 1993-1997 LT1/LT4 Engine Related

Fuel Pump, Injectors, Opti, or all of the Above?

Old 01-16-2015, 10:09 AM
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Fuel Pump, Injectors, Opti, or all of the Above?

So this is my issue, I have a misfire causing heavy bucking on heavy engine load (5th gear at 25 mph), hard starts that require me to crank the car twice to start, and dieseling for a few seconds when I turn the engine off.

Starting with the misfire, I've replaced the plugs, wires, coil, and ICM chasing this issue. The PCM throws a P0302 when this happens so I know which cylinder it's coming from. I do not notice the misfire when I'm driving normally, just when I drop into a gear to low for the speed. I thought this was my Opti, however, the vehicle doesn't misfire under any other circumstances, which leads me to my next issue.

Recently, I've noticed that my Camaro has a harder time starting than it used to. When I turn the engine, it starts up, sputters a bit, and dies, requiring me to crank the motor again, at which point it starts normally. I checked my fuel pressure, and it sits at 40 PSI during idle and drops to 35 when revving to 5000. I replaced my fuel filter, so I know that's not at issue.

Another issue I've had since I got this Camaro is that it diesels a bit after shutting off, leading me to think the injectors are leaking. However recently, it's gotten worse, to the point where the engine shuts off, runs normally for a split second and the dies again.

What is the issue here? I hate throwing parts at my car and if it's something expensive I really want to make sure it's going to fix my problems before I replace it.
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Old 01-16-2015, 05:28 PM
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Re: Fuel Pump, Injectors, Opti, or all of the Above?

misfire under load can be spark arc. check cyl 2 since that is the misfire code in a dark space. look for arcing. you may have to look from under the car while it is running. a spray bottle of water will help expose arcing

you may have other ignition issues but stumble/misfire under load (low speed/high gear) is often due to arcing
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Old 01-16-2015, 10:27 PM
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Re: Fuel Pump, Injectors, Opti, or all of the Above?

At idle with your fuel pressure gauge installed, see how the pressure changes when you remove the vacuum compensation hose to the regulator. Also see what the pressure does when you turn the engine off. A quick drop off could mean leaking injectors.
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Also please don't put your car in 5th at 25mph.
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Old 01-17-2015, 12:47 AM
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Re: Fuel Pump, Injectors, Opti, or all of the Above?

Originally Posted by shoebox View Post
Also please don't put your car in 5th at 25mph.
I won't anymore lol the gearbox doesn't seem to like that and with 200k miles and a dead 1-2 syncro I'm not about to stress my trans!

Anyway, I did notice that the pressure in the system would go down quickly after shutting off. I didn't test the pressure with the vacuum line disconnected (idk why...) but I will tomorrow.

I'm almost certain it's my injectors and an arcing wire now.

I'll test tomorrow and write back.
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Old 01-17-2015, 09:45 AM
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Re: Fuel Pump, Injectors, Opti, or all of the Above?

It's not just about "stress my trans"..... it's not good for the engine to be lugged at low RPM (830 RPM in 5th at 25 MPH with stock 3.42's).
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Old 01-17-2015, 11:23 AM
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Re: Fuel Pump, Injectors, Opti, or all of the Above?

Originally Posted by Injuneer View Post
It's not just about "stress my trans"..... it's not good for the engine to be lugged at low RPM (830 RPM in 5th at 25 MPH with stock 3.42's).
Good to know lol I didn't realize that. Although it's still not something I do regularly because of the misfire.

So I sprayed water on my wires and I couldn't find any arcing. I'm almost certain it's my injectors now. So should I get new injectors or remanufactured injectors? On RockAuto they have a couple of brands of remanufactured injectors for ~$30 (GB Remanufacturing and Autoline) and then the new ones are $60 and up.
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Old 01-17-2015, 01:36 PM
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Re: Fuel Pump, Injectors, Opti, or all of the Above?

You indicate you had code P0302 for a misfire on cylinder #2. Swap another injector with #2, and see if the code follows the injector from #2 to the new cylinder.
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Old 01-17-2015, 06:40 PM
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Re: Fuel Pump, Injectors, Opti, or all of the Above?

Op

don't just throw parts at it...first confirm if in fact you have a injector issue.

Do as Fred notes and swap it to another cyl to see if the misfire code migrates to that cyl

and while you do that CAREFULLY check the wires of # 2 injector plug for any breaks...including unwrapping some of the electrical tape further down the wire loom that contains the injector wires

and on checking for spark arc at plug boot end.....you really need to look closely and even from under the car as the arc can be very small and hard to see...especially if you still have the metal heat insulators on plug boot ends. arc can be between boot and inside of that shield making it VERY hard to see

confirm plug wires are set into the opti also...especially #2 since that is what misfire code you get. your opti cap could also be cross arching to but you would have to pull the cap off to confirm if that is happening
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Old 01-18-2015, 06:31 AM
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Re: Fuel Pump, Injectors, Opti, or all of the Above?

Might have to use a dental mirror to see inside then... #2 spark plug was beyond difficult to install, and impossible to see from the top or bottom. I switched the #2 and #4 injectors around so hopefully it sets a P0304 (the one time I'd be happy to see a misfire code). I still need to drive it around a bit and let it set the code. It's throwing a P0300 right now but if I run it for long enough it turns into a 302.
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Old 01-18-2015, 12:10 PM
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Re: Fuel Pump, Injectors, Opti, or all of the Above?

Try simply switching the injector wires with #4, leaving everything else in place. If the 302 code comes back it isn't the injector wiring. The switch out the injector with another one. If the code returns it has nothing to do with the fuel injection so you should focus on the ignition system. #2 is such a pain to reach make sure you double check that the plug wire is fully seated on the plug. You can sometimes get the feeling it's on when it isn't...
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Old 01-18-2015, 02:46 PM
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Re: Fuel Pump, Injectors, Opti, or all of the Above?

Originally Posted by bw_hunter View Post
Try simply switching the injector wires with #4, leaving everything else in place. If the 302 code comes back it isn't the injector wiring. The switch out the injector with another one. If the code returns it has nothing to do with the fuel injection so you should focus on the ignition system. #2 is such a pain to reach make sure you double check that the plug wire is fully seated on the plug. You can sometimes get the feeling it's on when it isn't...
I don't think you want to switch injector wires on a 96 to isolate the misfire. If it was a 93 (with batch firing), that might help isolate it, but not a 96.

Scanning for codes would also determine if there are any injector DTCs might be more helpful.
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Old 01-18-2015, 04:12 PM
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Re: Fuel Pump, Injectors, Opti, or all of the Above?

Getting the injectors out of sequence by swapping the wires can set misfire codes.
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Old 01-18-2015, 04:14 PM
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Re: Fuel Pump, Injectors, Opti, or all of the Above?

Originally Posted by timnfxr View Post
I don't think you want to switch injector wires on a 96 to isolate the misfire. If it was a 93 (with batch firing), that might help isolate it, but not a 96.

Scanning for codes would also determine if there are any injector DTCs might be more helpful.
It'll isolate it on any of them..batch fire or sequential. All that happens is the fuel 'puddles' behind the valve. The engine will run good enough to do the diagnosis. It's also very easy and quick...
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Old 01-18-2015, 06:03 PM
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Re: Fuel Pump, Injectors, Opti, or all of the Above?

The reason Electromotive gave up on their Opti-Eliminator was that the system got the injector sequence one crank revolution out phase 1/2 of the time. No ignition problem, because it was "lost spark". No injection impact on OBD-1 because no misfire detection. When they tried to run the system with the OBD-2 misfire detection, it set misfire codes . They never solved that problem. First hand info from an extended discussion with the Electromotive designer during a visit to the factory to show them the results of my OBD-1 install, one of the first ones.
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Old 01-23-2015, 05:24 PM
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Re: Fuel Pump, Injectors, Opti, or all of the Above?

Any update, OP?
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