Well I just got my new motor installed. Its a stocker with a lt4 hotcam w/ stock rockers in my 93 z28. My problems started when my main fuel lines started to leak, I pulled into the local chevy recycler to get some new ones when I noticed that it was dumping a HUGE amount making it absolutely totally unsafe to drive. I was in my good clothes so the guy offered to install them. Well he never blew them out and as soon as I pulled away I noticed a LOUD moaning sound coming out of the gas tank area. I am assuming the fuel pump was having trouble working correctly, and the car started to run REALLY rough I managed to call my dad who showed up with our trailer. When we got home we found that the return line was 100% plugged. So we blew it out and ran some injector cleaner through it. We also took it to the dealer put BRAND NEW fuel lines on it and had the injectors cleaned with nitrogen. Now the car still idles very rough and acts like its running on 7 cylinders when I take off from a light. It also begins to surge and throw me forward and back in the seat til about 2300 rpm at part throttle (never tried WOT). Intermittenly there is a loud tacking sound coming from what it sounds like is the #6 or #8 injector. (I pulled both valve covers and checked valve adjustment they were fine) The dealer thinks its because the computer has yet to be tuned. I think its one of the injectors fouling up. Should I replace the injectors when I get it tuned? Will it still pass smog with new injectors? Thank you very much for taking the time to read this.


P.S. they said the computer is registering misfires due to the cam? If so, would that make it run rough?

 

Cmon guys! I can't drive this thing until I figure something out! ANY help is appreciated

 

If you put on some lines past the filter that may have had trash in them, you probably clogged some injectors.

 

Do you think the injectors could still have some junk in em after the dealer did a high pressure cleaning? If so, should I say screw it and have the guy tune for some new injectors

 

Something doesn't add up. You said it was a 93. Up until 96 there was no way for the PCM to detect misfires. I doubt you are using a PCM with OBDII, so why would "they" say it was detecting misfires? Are "they" wrong or do you have and OBDII computer AND a crank sensor?

Next line of thinking. How long did it run before you had the leaking problem?
Did it ever run good?
You said the return was completely clogged, yes? This would cause the pressure in the feed line to shoot up very high correct? Will high pressure cause a problem with the FPR diaphragm? Not sure but probably. Now if you have a hole in the FPR diaphragm, fuel will be leaking into the intake, richening up the mixture and causing it run crappy. Pull the hose off and see if it's wet.

What does high pressure do to the fuel pump? May be time to put a fuel pressure gage on it when you drive it around.

One last thing, surging is usually from running lean. Contrary to what I said about the FPR above but checking the vac line takes 20 seconds and you did have HIGH fuel pressure for a while. A vacuum leak could cause a lean condition. But then, so could clogged injectors that may have not REALLY been cleaned by a dealer claiming to use nitrogen Yeah right.

 

uhhh it is a 93 (speed density) and "they" are the local dealership. The car did use to run good before the fuel line problem, i changed all 3 lines 2 times, and the first time it appeared to have some fuel in it. The vacuum leak seems plausable due to the fact that the engine changes a TON once a load is put on it (air conditioning), IN FACT, the engine runs SO differently it will overheat if sitting at idle for a period of time JUST because the AC is on, thus showing a lean condition. So I am definately going to check that right away, so if it does end up being the FPR should I get aftermarket or get a stocker replacement? I think what I am going to end up doing is buying new injectors, FPR, and blowing out all the lines carefully. I guess this is reason #4945903 do stuff yourself if you want it done right

 

Well I think you proved the dealer either doesn't know what they are talking about. (detecting misfires in a 93 that can't do that) or they are flim flam artists. (Cleaning injectors with Nitrogen) Either be the case, the injectors are clogged with S!@T. you don't necessarily have to change them. They can be sonicly cleaned and flow matched. However, the OEM units use a single spray pattern and aftermarket USUALLY use a multi hole cone spray pattern so typically aftermarket give you the best the performance.

 

Thanks for the info, I appreciate it. I think since I have to have the whole fuel map re-done anyways that I am going to buy the 30# Accel injectors from summit and take all the lines down and blow them out


EDIT: I checked the fuel pressure, its 42-44 shut off, idling its 38-40, and at 3000-4000 its 35. How do those numbers sound???

 

Heard really bad stories using Accel injectors.
Might want to take a look at these.
http://www.holley.com/types.asp?type=69
I'de trust Holley any day, used their products when I was a younger man.
Your numbers look ok accept the heavy cruising pressure is dropping and it should have gone up. What does it do at idle when you pull the vac line off? Is the vac line wet? I don't understand why it's higher when off then it was at idle. Any ideas? Or did I misunderstand what you meant?

 

Well my understanding (if its anything like the efi on my 68 camaro) the vacuum pulls pressure down. So when the engine is running it has lower pressure. When I said the pressure was at 35 at 4000 rpm I was sitting in the driveway doing that With my guage there isn't an easy way to see it while driving

EDIT: What is the stock size injector in a 93? Since holley has a range of sizes and I actually have a set of 42 lb/hr on my 68 camaro so I know they are a good brand and they perform very well, i should just get the stock size or maybe a TINY bit bigger than my stockers from holley. They are high impedence injectors, is that what I want?

EDIT: Well I read further on their website and high impedence is what all the smaller injectors are So thats what I'll get a set of 24 pounders