Starting problems

[BSHeiz]

Hello! I am new to this thread and I have a question that I hope someone here can answer. I have a 1995 GMC Sierra with a 5 spd and new 350 in it that was installed by previous owner in 2006. The engine has about 25-30 thousand miles on it and when running is a strong runner! The problem is this.... A couple of months after I bought it it would not start, unless I would get it rolling down the hill, pop the clutch and then it would fire. No problems the rest of the day and would start fine. I returned to the car lot where I bought it from and they said they would take it to their mech and he would fix it. I thought that the fuel pump was bad and asked them to replace or test it and so being they had it tested and it was working fine. The mech replaced the sending unit and it worked fine, until about a month ago when the problem resurfaced. Some days the truck will start and run just fine, other days it will not start unless some either is shot down the TBI, and its not much or unless you bump start it. I have replaced the fuel filter, had the system flushed and still nothing seems to help. I have taken it to mechanic here and no one can seem to find the problem. It is driving me nuts! It is a **** shoot on when I come out in the morning whether or not the truck is going to start! Once I get it started it runs fine no hesitation or nothing. I have a K&N airfilter on it and have run a can of seafoam through the gas tank. Other than replace the fuel pump, which when I dont think needs to be replaced because when you turn the key on you can here it working. Any ideas???????? Thanks!

[75K30]

Welcome to the site:
Interesting that it starts fine when bump starting it.
I might suggest looking into a couple of things. The first would be the fuel pressure regulator. Verify proper operation. May have a problem getting the initial fuel to the cylinders.
Next, may be a long shot, but it does make some sense, and that might actually be the ignition switch itself. Though this does not explain why it does not do this when warm, it is worth looking into.
Could also be an oil saturated MAF sensor. Rather common with K&N typr filters that get a little too much oil applied.

[436'd skylark]

try a map sensor. TBIs have a way of acting very funny. it is such a simple system it can be very frustrating to diagnose. next time its not starting, pull the air filter and see if the injectors are firing, very obvious to tell. if they are, you either have bad fuel, or a spark issue. raw gas from the injectors has the same effect as shooting ether in.

no fuel shooting leads either means your fuel pressure is in the toilet or the injectors are not recieving signal to open. I'm leaning towards a distributor problem.

heres my theory... the pick up coil is weak, sending a weak signal to the module. sometimes its strong enough to fire, sometimes its not. pick up coil is essentially an electromagnet in reverse. the faster the shaft spins, the stronger the signal, cranking is sometimes too slow, or the spark is too weak when the motor is cold to fire. spinning it faster, by popping the clutch, or shooting extremly flammable (ether) band aids the problem, and the truck runs.

somewhat explains why it runs fine when its running, and why it won't start sometimes. the pick-up coil and module act as a crank sensor, and let the computer know that the engine is turrning over. nobody ever replaces the pick up coil, so I'd start there.

[BSHeiz]

Thanks for the info! I will check those out and keep you posted!

[Hayden]

About a week ago my truck was running fine and started every morning like it should. Then 1 morning running a tad late for work I tried to start it and it almost fired right away but didn't and then just kept rolling over. I sprayed starting fluid in it and it'd fire right up with no problem.. Well one day on my way home from work my acceleration would just bog down if I tried to give it gas while going over 60 mph and then it got worse from there. So I ran a fuel pressure test and it was fine (52 PSI)when I got home that day. Next morning same thing. I had to spray starting fluid in it but I didn't.. I ran the fuel pressure test instead and it flunked bad only peaking at 35 psi and then would decrease bad from there. I happened to have a new fuel tank and AC Delco pump sitting in my other truck I was parting out so I exchanged it and have been running great ever since. Just Because a pressure test is fine when you try it once doesn't mean its a good pump. Try a pressure test on it before starting it up in the morning.

[436'd skylark]

thats a good point, but TBIs aren't very picky about fuel pressure. they will run on much less than 15, they just won't run good.

[Lhasty]

Hi, I probably know very little compared to most who post here, but could the problem be the starter solenoid? I had a boat with a 4 cylinder GM engine that wouldn't fire up if it had set up for more than a couple of days. I battled this problem for many years. I finally figured out that the washer in the solenoid that makes the connection to the ignition system was not making good contact when the solenoid and starter was energized. I had power to the distributor when the starter solenoid was not pulled in, but it lost it when you turned the key to start. Once I finally was able to start the engine, the problem with starting went away, unless like I said, it wasn't used for a few days. Anyway, I can't remember how I discovered the problem with the solenoid, but after I replaced it, I never experienced the problem again.

[1979_4x4_Plow]

ugha...has anybody thought about replacing the fuel filter and run fuel injector cleaner? my girlfriends car was acting this way and it was because the fuel filter was restricting the flow of the fuel. it would stumble backfire and everything. ended up not getting enough fuel to the engine due to restriction of the fuel filter. the fuel filter was only 2 months old but i had done work on the fuel pump so stuff got sucked up into the new filter.

[Hayden]

might want to think about replacing her tank then. Sounds like alot of debris is in there

[BSHeiz]

Fuel filter has been replaced and fuel system has been flushed. So I dont think that it was that.