I jsut read through all of the threads posted by other members and found my situation to differ from theirs so I figured I would post my own and try and get some help. So, here are the details -

I have a 1994 C4 and I have had it for about a year and a half now. Ever since about 2 months after the purchase, it has been hard to start. It started out that it was just hard to start when it was hot out. Then, it switched to being hard to start all the time. About 8 months ago I had an engine rebuild. Had it bored thirty over, new cam, rebuilt heads with 2.02" valves, and a few more goodies.

I got the car back and it started fine for the first 2 days. Then it went back to crap. The car starts fine if it sits for like 2 or 3 days without being run, but the problem is that its my DD. I had someone check the fuel pressure and it was where it was supposed to be.

I went down to Carolina Auto masters to have it Dynotuned and was told that I was down 2 cylinders because two of the spark plug wires were arcing between some weird stuff. The problem was temporarily fixed. Jeff Creech told me that I should change my fuel pump because he said thats what my problem is. I am not calling him a liar cause I know he knows his stuff, but I replaced the fuel pump 2 days ago and it started fine for the first day and a half. Then this morning when I was going to work, it took a while to start, and the same thing coming home from work today. When I say it takes a while to start, im not saying like 2 or three seconds.. It is as much as 8-10 seconds of the starting noise, but for some reason it sounds louder and more high pitched.

I believe my car is missing at least one cylinder again, if not the two that it was missing. Jeff told me I should also have the distributor cap and rotor replaced. That is going to be done in about 2 weeks. Now, when the car finally started everytime before the fuel pump was replaced, it would smoke at startup. I cant tell if it is blue or black, but i know it smells like fuel. For the few times when it didnt take long to start after I replaced the pump, it didnt smoke. Now, when I started it coming home from work, it smoked again.

PPPPLLLLLEEEEAAAASSSEEE help lol. It is soooo embarassing when I get in my car to have to wait until nobody is around me to start my car cause I dont want them to hear the noise and I dont want to smoke them out. Thanks in advance!!

Matt

 

Did you replace your injectors during the rebuild? Could be a leaking injector causing all of your problems.

 

Thanks for the response. And, the answer to your question is no. I didnt replace them during the rebuild, but I replaced them after the rebuild and (on the advice of the idiot mechanic who also happens to be my neighbor) I put 30# injectors in there. When I got the car tuned, I am pushing less than 300hp to the wheels. There is no reason to go 7#'s more than stock for that little bit of power. The end result was my engine basically drowning in fuel and bogging down. I had to change back to stock. During the 3 days I had the new injectors in, it still started the same as it does now. Thanks again!

Matt

 

Your symptoms are of leaking injectors causing a too rich condition to start. Measure the fuel pressure on the shrader valve on the end of the fuel rail. Turn on the ign for more than 2 seconds and turn the ign off and see how long it takes to lose fuel pressure. If it falls quickly, you may have leaky fuel injectors. Proof is to remove a few spark plugs and see if they are wet.

 

If it smells of fuel...Fuel pressure regulator is a good bet.

Pull the vacuum line off the regulator (at the regulator, not at the manifold). If there's any fuel in it AT ALL, the regulator is bad.

Considering you had two different sets of injectors and a different fuel pump, you can pretty much rule those out IMO.

Leaking injectors are easy enough to check for on the LT1 however...Lift the fuel rail up and away from the the intake with the injectors still attached. Turn the ignition key to "run" to cycle the fuel pump. If the injectors are leaking you'll immediately see it. It should take someone with nearly zero mechanical skills about 30 minutes total to do this. If you have some skills, even less

Another way to check to see if it's a fuel issue is to scan it with a decent software package. If your long term fuel trims (LTFT) are a lot less than 128, then the engine is rich and the PCM is pulling fuel.

A bad Opti will also cause hard starting. Replace the whole unit, not just the cap & rotor if you decide to do this. Pre '95 units are notorious for moisture intusion that also ruins the bearing.

Since it started fine right after the fuel pump and then the issue re-appeared, to me that points to fuel and specifically the FPR as I mentioned above.

 

Thank you very much for your responses. I will try everything I can today. I was actually the one that changed the injectors so I know taking the fuel rails out wont take more than a few minutes lol. I really hope it is something simple like the FPR or something like that. I am just really tired of it taking so long.

Another sympton I forgot to tell you about was the fact that if I start it up and drive it for a little bit and then let it sit, for example, for about how long it takes in a convenient store; I go back out to my car and it starts right up. Any longer than about 5 minutes and it takes a while for it to start.

Thanks again!!

Matt

 

Will a leaky pressure regulator allow the fuel rails to drain? My starting issues where about the opposite of yours. Mine started great cold but would crank awhile when I came out of the store. My issue was injectors. One was completely dead and some where leaking. New injectors and it's like I got a new car.. Of course all the other issues are taken care of too. If you can't do the work yourself on this car, you better have a lot of money on hand because as soon as you get one thing fixed, he next one will break (why I like replacing "systems" instead of individual parts).. Arlon

 

Same response...FPR

 

It's not the lack of fuel in the rails and realistically a failed FPR doesn't "drain" the rails. When the FPR fails, it's really the diaphram inside it that separates the fuel (wet) side from intake (dry) side failing. As a result when you try to start the engine the combination of fuel pressure from the pump (~40lbs while cranking) and vacuum draws raw fuel directly into the cylinders. This added fuel is way more than what the engine can use so basically the engine is being flooded. During cranking the o2 sensors are not providing feedback. Therefore the PCM is relying on a hard coded fuel map which assumes the FPR is ok. When cold, the engine needs to be a little rich anyway so if it's a minor FPR leak the car may start fine. When hot, different story.

He already tried one new set of injectors and there was zero change so I fail to understand why some of you guys want to continue to throw money at it. Perform the appropriate trouble-shooting. Patience is a virtue.

 

Thanks again for the responses. I am waiting until tomorrow to check the FPR. Should I check it just after I ran the car for a bit and drove it, or should I check it cold? Thanks!

Matt

 

Start it and then turn it off and check it. As soon as you turn the key to run the pressure from the fuel pump will force fuel into the FPR vacuum line if the FPR is bad. Takes at least 30 seconds to do this check

 

I read your post a couple or three times and I was puzzled by the above statement......

Does your engine have a regular distributor, distributor cap and rotor button?

It's supposed to have an OptiSpark ignition system... is that what you have?

Also.... you stated you got a new cam, heads and few other goodies....

Did you have any PCM tuning done afterwards?

I'm just wondering exactly what you have got there. It 'may' be pertinent to anyone guessing at a diagnosis here.

Seems like any competent mechanic would have done a fuel pressure and regulator test already.
Of course, it's easy to miss the leaking diaphram in the regulator sometimes.
But an ENGINE SCAN would have caught it with the BLM's.
ANother hint is the fuel pressure will 'jump' around if the regulator leaks.
That's all predicated on someone that knows how the 'system' works was trying to solve this mystery.

I think Jim' probably hitting the bullseye....

 

Ok, in respone to VetNutJim, I was told that I could just replace the Distributor Cap and Rotor. I am not too familiar witht he ignition system on the LT1. You may be right and I may have to replace the whole Optispark.

As far as PCM tuning, is that whats done with a Dynotune? Because I stated above that I have had it dynotuned. But if thats not the same thing, then I would say no because the guy that did the motor work to my car slacked off in quite a few areas and I wouldnt doubt if there were things he was supposed to do that he didnt do.

I took the car to a place called Tidewater Corvette here in Hampton Roads and the guy there checked the FPR a few times and said that it looked fine. But, this was also about 6 months ago.

As always, I appreciate the help and if there is anythign else you need to know, just ask and I will let you know to the best of my ability (which isnt saying much )

Thanks


Matt

 

Dynotune is just tuning the PCM with the car on the dyno while gathering a/f raio data. Since all engines vary, a properly done dyno tune will be better than an over-the-counter mail order tune.

Since checking the FPR takes all of 30 seconds, go do it If you don't have 30 seconds to spare, then assume the FPR is good and change the Opti...after verifying all the plug wires are installed correctly.

The Opti has a cap & rotor (same in function as a traditional distributor, but much different looking) as well as the Optical section. The cheap route is replacing the cap & rotor. Having said that, I like replacing the entire assembly...especially on pre-'95 LT1s since the Opti on those engines isn't vented as well as the '95 & up units (which...with more money and more work can be retrofitted to the early engines).

 

Again, Thank you for the reply Jim. I just took my 30 seconds of hard work outside lol. I checked the FPR vacuum line and when I checked it, although there was no liquid fuel in the line, I smelled the line (I am kinda like a child and I have to smell everything) and it smelled strongly of gas. That could be because it regulates FUEL pressure lol. But I am not a mechanic and I was just stating the obvious.

I understand what you mean about replacing the whole Optispark. I looked online and they are very expensive. I understand that cheaper is almost never the better way to go, but what are the non-obvious advantages of buying the whole unit rather than just the cap/rotor? I appreciate your help!

Matt

 

Re the Opti....the biggest advantage is that you get all new electronics and a new bearing by replacing everything. As Opti's age, a couple things happen...the cap and rotor wear out, the sealed bearing goes bad, the debris from the failing bearing hurts optical sensor performance.

Personally I'd scan the PCM data to see what the fuel trims look like.

Extended cranking times when hot are an Opti trade-mark. Do you know if it's original?

Did you verify all the plug wires are connected to the correct terminals on the opti?

Do you know the plug wires are good?

Try this test...Run the engine until it's hot (ie such that it'd be hard to start). Turn the engine off and disconnect the battery or pull the PCM fuse. Wait whatever typical amount of time you've waited in the past such that the next start attempt would normally result in extended cranking. Reinstall the fuse or connect the battery. Try to start the engine. Did it start right away or still crank for a long time?

 

I posted last week about the same problem! My 94 is stock, with no mods......all my problems are hard starting anytime. It runs fine when running.....I am interested to see what the problem is...I have checked some things, but.......Thanks for any help!!
Rex

 

Thanks again Jim! I will definately be sure to do that tomorrow, as it is too late to do it now. Its 1am here! Now, when you say that
"Extended cranking times when hot are an Opti trade-mark"
, It doesnt just take a long time to crank when hot. It could be hot or cold or lukewarm. It just always takes a long time... UNLESS I let it sit for a few days. Or unless its within about 5 or 10 minutes.

Now, to the rest of what you said; The plug wires that were put on after the rebuild I had done were 8.8mm ACCEL wires. I had those on there before and they just put them back on. The idiots didnt route the wires right and so they were resting against the header tubes and they melted. When I told them they needed to replace them, they put s**tty 7mm No-Name Brand wires on. They are actually what is still on there. But, I figured if I was going to replace the cap/rotor, I might as well replace the bad wires and the plugs while it will be easy. I just dont have $550 to spend on a new Opti right now. Regardless, though. If I have to spend the money, I have to spend the money, right?

How do you scan the PCM data? If that is what you would personally do, I will probably end up doing it because I want to try everything to get rid of this problem. As always, Thanks Jim!!

Matt

 

There are so many people that have this very problem myself included except mine will only do it every now and then. I checked the injectors and their not leaking so I guess I'll go check the FPR if I can find it.

 

You have the classic symptoms
Take that FP and shove it up your mechanics keester. I love it when mechanics throw parts at a car, dont fix the problem and charge anyway..."Oh, it needed it anyway."