Help with stuttering problem

[94 formula]

I posted last week that after replacing almost my entire ignition on my car that I still had a stuttering problem. Its actually worse than a stutter now the car will hardly run. I put on a new IC module today and that still did nothing. So I figured it must be the fuel pump and tested the pressure which read 39 before the car was turned on and dropped maybe one or two pounds after I ran the car. I know that is a hair under what it should be but only a psi or two which shouldn't affect the car that much. I'm beginning to think its something internal. I took off my oil filter and cut it in half then spread it out looking for pieces of a bearing or anything to point me in that direction but it looked fine. What should I do next? Any advice or experiences would be greatly appreciated.

[97LT1Z28]

I had a similar problem with mine - it turned out to be the cap & rotor on the Opti. It had 107,000 miles at the time. I tried to find your post from last week so I could get some more details on your problem but no luck. Can you tell us what's happening? Does it happen at an idle, while driving or under hard accelleration? Does it happen at low RPM's or towards redline?

[95z28]

Im pretty sure he just did his opti if i remember correctly.
What aobut your fuel injectors, pump etc ????

(my car just started to do the same thing its a pain in the rear)

[97LT1Z28]

I found your other posts . . .. you really did replace the whole ignition system!!!! That probably eliminates any problems related to spark . . . On my third generation Camaro, I had a MAF sensor go bad - it didn't trigger the SES light, but it screwed up the injector pulse which rendered the vehicle almost undriveable. It sputtered, missed, you name it. I also agree with the previous post. Check your injectors to see if they are clogged or not functioning properly.

[94 formula]

I tested the pump it was at 39 psi which I know is a hair low but not low enough to cause this. The car has a hard time turning over but will always start. I probably described it wrong as a stutter it has actually gotten much worse than that. The car hardly has any power at all. If you'd floor it in first I'd guess it would probably take about 10 seconds to reach 4k rpms just to give you an idea. I've replaced every component on the ignition system within the last 10k most of it has just been done. I've checked over almost everything under the hood no burnt wires, bad connections, ect. I'm really not sure where to go from here.

[97LT1Z28]

Did this problem start happening all at once or did it get gradually worse and worse??

[N20LT4Bird]

39 PSI is low.....did you check it under load? You really need to watch the fuel pressure as you accelerate. It should not drop at all......if it does, you pump is not keeping up...

[wolfdogs]

scared me... i thought i was gonna have to tell you to put "nfb" next time and recommend a speech therapist..............

[94 formula]

Wolfman, I looked at your post and went back over mine for a good 5 minutes until i finally got what you meant lol. I just took nightquil and have a 103.5 degree fever.

Back to the car....lol. What do I need to do to test my injectors or make sure their not dirty? The car had a stumbling problem for awhile and I started working on the ignition starting with plugs and wires then 02 sensors then opti, coil, coil wire, IC module. The car had been running with a miss and got worse right before I changed the opti. After I changed my opti the car ran great for about a day. The only thing I noticed was time or two I punched it and around 5k it felt like I hit a limiter it never did it again so I thought it was just a fluke. Then it just all the sudden started running like crap about 50 miles after I got the opti done and thats where I'm at now. I've replaced my coil, coil wire, and IC module since then and that has done nothing I'm really not sure where to go from here. Also my fuel pressure was 39psi when I turn the ignition to on and maybe drops a pound or two when I idle it. I can't really drive it to know if it drops anymore underload.

[Trans Am]

did you try with a new fuel filter? its pretty cheap and i suggest to do that before replacing the fuel pump because its not an easy job

I had the same problem and it finally didnt start at all so I ended up replacing almost all the ignitinon and the fuel pump

[Injuneer]

To test the fuel pump correctly....

Start the car and let it idle. Remove the vacuum compensation line from the pump (put your finger over the end, so there's no vacuum leak) and you should see 41-47psi to be in spec.

Reconnect the vacuum line. Fuel pressure should drop in proportion to engine vacuum, so you will see an 8-10psi drop with a stock(ish) cam.

Tape the gauge to the outside of the windshield and drive it as hard as you can. Fuel pressure should never drop below 40psi at full throttle (no vaccum).

Have you ever had the PCM scanned?

[94 formula]

A friend is letting me borrow his cable next weekend I'm going to get a freescan file of it and post it. Also if the pressure is only 5psi low will that cause a bad miss? I won't be able to get back at my car until I'm home from school next weekend and my car hardly drives at all is it alright to just take it for a quick ride to test the pressure even if it is missing so bad?

[Injuneer]

With a 5psi drop in fuel pressure, you're looking at a 6 to 7% shortfall on fuel flow, compared to what the PCM is expecting the injectors to flow. That would actually help the WOT A/F ratio, becasue the stock target A/F ratio in PE mode is way too rich.

If you are already down 5psi at idle, there's a good chance its even worse at WOT. Have you ever changed the fuel filter? Have you checked the vacuum line on the fuel pressure regulator for signs of a faulty regulator (liquid fuel in vacuum line)?

[94 formula]

The fuel filter has been replaced not to long ago. I'm writing everything down so I know where to start next weekend. I'll get it hooked up to my computer and get a good scan of it and try getting fuel pressure under load. Thanks alot for the ideas and advice everyone I just hope I can get her running before it gets really nice out.