DMD95z

Hello, long time lurker first time poster. For the last few weeks I have been reading the LT1 Section but no luck finding my exact problem. Last week I finally gave up trouble shooting and took my car in to the GM Garage. They informed me I had one serious leaking injector. I had that replaced as well as plugs,wires,fuel filters. Also they checked fuel pressure which they said was normal. I now have the car back and still have the same problem. The problem is first thing in morning the car will take a couple 3-4 second cranks to start. Also if the car sits in the my heated shop at work all day long it will take 4-5 3-4 second cranks before it starts and when it does start it idles rough for about 10 seconds, after that it idles, drives perfectly. Today I discovered if I hold car accelarator to the floor it starts almost immediatly on the first crank. Any of you LT1 gurus have any idea what might be causing my start problems. Any insight at all would be great as its driving me crazy. Thanks In Advance.

RickyMartinZ28

iTrader: (5)

I have no idea. Mine always busts off immediately. Good Luck, sucks that GM raped you.

-Rick

Well, actually mine had a similar problem once. My idle bypass in the Throttle Body got pretty dirty and it didn't want to start real quick and it sometimes idled strange. I'd yank the TB off and clean it really well with some carb and choke cleaner, it can't hurt anything. Mine got nasty cause I ran and K&N filter with a little too much oil one time. Sucked oil into the intake and made everything nasty.

-Rick

Camaro_freak

iTrader: (1)

First thing I would do is check fuel pressure again. Get a fuel pressure gauge, attach it to the schrader valve at the back of the fuel rail, and turn the key to the "run" position for several seconds, but don't crank. Turn off the key, and see if the fuel pressure stays up, or if it bleeds off quickly. I had a fuel pump going out on my Grand Prix, and the longer cranking was the symptom (confirmed by the fuel pressure bleed off test). Unfortunately I put off fixing it for too long and ended up getting stranded one day with a dead pump. It may or may not be your problem, but it's something easy to try.

Revelation Z28

iTrader: (10)

i had an extended cranking problem the day i bought my car. knew it was the fuel pressure regulator first moment i started it. ever since 1/2-1 crank starts it right up. look into replacing it.

BOLO

iTrader: (40)

I have a 94 z28 and have owned it since new. It's not stock anymore. Modifications have been done through the years. The car has 73,000 miles now. The car starts normal but not like when it was new. Just recently, I've added a nitrous system and replaced the stock fuelpump w/ a Walbro 255lph and to my surprise, the car is starting the way it used to when it was new. So, it's something to think about. Good luck! Oh, also check fuel pump relay located near driverside left foot rest.

DMD95z

Appreciate the quick replies. I was skimming through the owners manual and noticed it says if car is flooded to hold accelarater to the floor which tells the injectors not to fire. With the pedal to the floor it starts immediatly. Im gonna pickup a gauge today and check the fuel pressure myself and maybe go ahead and replace the fuel pump regulator at least maybe iliminating those as problems.

DMD95z

Well I am Still suffering extended cranking problems, Ive replaced, Opti, Fuel pump regulator, spark plugs and 2 injectors, also Ive checked for any Vaccum leaks. Ive had it scanned for codes which there is none reported and the SES light is not on. Also the fuel pressure never drops below 42 nor rises above 50.The Car still has an extended crank problem if it sits for more then 30 minutes. Doesnt seem to matter if the engine is cold or warm car is outside in -20 or parked in a heated garage. The car runs and drives perfectly once started. 1995 Z28 M6 if it makes any difference. Any more insight into the problem would be greatly appreciated , very frustrated at this point. Only thing that seems to work is hold the throttle to the floor and fires and starts almost instantly. Also is the car is 100% stock right down to the air intake.

Jditlfm

iTrader: (26)

When you cycle the key fuel pressure should be 40-45 Psi. Then when you shut the key off keep watching the gauge. It should hold pressure for around a half hour this is called a residual pressure test. Let me know those test results. I am willing to help you out if you want to go through the steps....

DMD95z

Thanks for the reply I will check the fuel pressure leak down numbers tonight and let you know.

DMD95z

Ok so I hooked the pressure tester to shrader valve, Turned key fuel pressure goes to 43. After 5 minutes drops to 38 , another 5 minutes its down to around 20. in 30 minutes its down around 10psi and seems to stay there.

BTW I really appreciate the help your offering, Ive had it at GM garage twice and they cant figure it out.

joelster

Try starting your car in this manner. Turn the key to "ignition", then WAIT for 3 seconds. You will hear the fuel pump turn on in back, and build fuel pressure. After it shuts off, start the car. Let us know how quickly it fires.

Jditlfm

iTrader: (26)

Ok that sounds like it could be your problem. There is a anti drain back valve in the fuel pump assembly in the tank. When you did the fuel pump did you just replace the pump or the whole sending unit? What brand was it also? Try this now. let it sit again so it would normally take a long time to start. When you go to start it just turn the key on till you hear the fuel pump come on and shut off, but do not start. Turn the key off and then back on and do the same thing, do this cycle a total of three to four times. After that try and start the car and see how long it takes. What you are doing is just making sure the lines are filled with fuel before you start cranking. If the gas is draining back to the tank after sitting some time the fuel pump is having to fill the lines again and that will take some time. (hence the long cranking time) If it's not the problem then we will go from there.

DMD95z

I went out this morning and turned the key on for 3 seconds 5 times,. I could hear the fuel pump prime each time. The car fired up instantly. I will test this theory again in an hour or two. Also the fuel pump has been replaced because GM swears theres nothing wrong with it. The exact parts that have been swapped out are as follows, 2 Injectors, Opti, waterpump, Spark plugs, wires, and fuel pump regulator. Once Again I really appreciate the help. Will post in about an hour with results of second test.

MysticLT1

iTrader: (1)

Im curious to find out what it is my car has the same exact god damn problem since i bought it i also replaced everything you have the only difference is that mine is a 96 hmm i will try jditlfm's theory

DMD95z

Well I did a second test, 5 , 3 second key turns and once again it started on the first crank not quite as quick but way quicker then other time. Where do I go from here ?

Thanks In advance

Jditlfm

iTrader: (26)

Ok this is good you have a direction in which to work in. This is how the fuel system works the fuel pump pressurizes the line and the fuel pressure regulator modulates the fuel pressure with vacuum off the engine. I took the time to dig up one of my books from school for a pic for you. What is happening in your case is fuel is returning to the fuel tank too quickly and way sooner then it should. This can be caused by one of two things, one is the fuel pump allowing fuel to come back into the tank through it or a internal check valve in the pump or the sending unit( depends on the manufacture) or the other way is that the fuel pressure regulator sticking open and allowing fuel pressure to return to the tank through the return lines when its not supposed to. Now this is what you have to do to figure out which one it is. If you can disconnect the fuel return line at some point and block it off then do that but what most people do is pinch the return line as close to the regulator as possible. This is where good judgment comes into play you have to find the closest possible location where you are safely able to pinch the return fuel line without causing damage. Snap on and other manufacturer's make a special tool for this, but you should be able to use vice grips and a towel placed over the teeth as to not damage the line. Setting the vice grip clamping force is very important as to not ruin or crack the line. So as i stated before use you best judgment. If you break this line you will be replacing it so keep that in mind. By clamping this line we are either going to eliminate or find if the regulator is the problem. What you need to do is run the car after you find where you want to pinch the line and then shut the car off and clamp the line before pressure starts to drop. let it sit for as long as you stated and then try and restart it, you can also monitor pressure with the gauge. If the car starts right up then the fuel pressure regulator is faulty if not then the fuel pump could be the culprit. Let me know the results.
-Jon

joelster

After you do this and find the problem, make sure you print up this thread and go back to the gm dealer who previously worked on your car and tell them how stupid they are. How much money did you end up spending on parts/labor at the dealership anyways?

DMD95z

Well so far the bills have have come to a grand total of 4800.00$ , however im only on the hook for about 800.00$ of the because of the warranty. I have talk to the service manager of the GM Dealer and he has agreed to take the car back on weds and diagnose it for free and cut me a huge deal on the whatever it takes to make it right. Actions speak louder then words so we will see how it goes but i think he realizes he cant get my warranty to approve anymore work on the same problem. Once its finally fixed I will post back for sure. At least now I know the fuel leakdown is almost garranteed part of the problem. Once again I will post back with results when its back to 100%. Thanks again for the information and all the help.. Hopefully this thread will help someone else.

Jditlfm

iTrader: (26)

ok just let me know one thing i forgot to mention is that the one other problem is a leak somewhere in the fuel system as a third possible cause. Injectors a fuel line or a fuel filter. From what i read you don't want to take the diagnosis any further and just let the dealer figure it out?

DMD95z

Well if the dealer wasn't saying they are gonna make it right I would be all over it, but now that the dealer has agreed to look at it and make it right at there cost. From here on Ill hold off and see what they tell me. Ive checked for any external leaks and they replaced two of the injectors already. The second time it was in they swore it wasn't fuel rail or injector problem. They diagnosed the opti was putting out a weak a spark. I didnt really believe that as the car ran perfectly once started but when warranty agreed to let them do it I said sure since it had 65k on it and was most likely the original. All this work for the same problem puts me in kinda a bad position. As the warranty isn't willing to put anymore money towards the same problem. My biggest fear right now is it is an injector leaking and dumping fuel into my crankcase but I do not see any evidence of that in the oil. No smell anyway. Also fuel filter has been replaced and no evidence of leaking. The only thing that baffles me is why holding the accelerator to the floor starts the car instantly as if clearing a flood situation.