1988 GMC 4.3 1500 TRUCK STARTING RUNNING PROBLEMS

I have a 1988 gmc truck 4.3 engine and about 2 weeks ago I pulled up to a stop sign and it quit running it was about half way warmed up, so I turned the key off and it restarted but it was running kind of
weird.
I noticed the voltage was kind of low so because the battery was kind of old I got a new one and installed that and did not have any more problems that day or evening and I started it many times.
The next morning I went to start it and it would start and run for a few seconds and quit, so I had a can of starting fluid and had my son turn it over and when it tried to stall just gave it a tiny squirt of starting fluid and after it warmed up a bit it ran just fine.
I kept having the starting problem so I took it to the local mechanic and he found the alternator was not producing enough voltage so he put on rebuilt.
Voltage is now normal still had the starting problem.
Then checked the fuel pressure and found that is as going below specs intermitently and so I had another valve body that he put on, that fixed the fuel problem at the time and it started good.
Went to pick it up and it ran kind of funny and the next morning same problem.
I drove it yesterday and was going down the freeway about 70 mph and it just quit but restarted again, and I am still having the starting problem.
It takes about 5-6 times starting before it will run and if it sits longer than about 2-3 minutes it takes about 2 times to make it run.
I have put on a new temperature sensor, and I tryed a used computer from a junk yard same problem.
I had a new fuel pump put in about 70,000 miles ago. because of lack of power.
Code readers do not show anything and the light does not come on.
Can someone please help!!!!!!
THANKS GARY
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If you have a vortec engine it has an octopus fuel delivery system. To make sure if you can see the injectors sitting in the throttle body it is not vortec, or you can see fuel injectors it is not vortec. If it is vortec then it has a fuel pressure regulator and injector hoses and poppet injectors inside the intake manifold under the upper manifold . Sometimes the fuel regulator starts to leak, take out the plugs and see if the plugs are fouled only on one side, it usually means the fuel regulator leaks into one side of manifold and whole regulator, injector assembly needs to be replaced, you can tell by removing valve on top of upper manifold and looking in with a flashlight, if one side is washed clean by gasoline then regulator leaks.
gsprinklerman wrote:

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It is not a vortec just a TBI and it just stops completly no missing. I think it is the fuel pump that is involved some way or the wiring to the pump or the relay but I don't know how to check that myself. It will run if I squirt a little gas down the TBI so it keeps running then after about 2 minutes when it is cold it will run and then starts quicker when warmed up very strange, even if I just start it and it quits several times it will run without the spray of gas, so many starts I had to put in a rebuilt starter. I had a new fuel pump put in about 1 1/2 years ago. thanks for your feedback, do you have any other ideas?
snipped-for-privacy@netzero.net wrote:

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I'll go one further with you. I have a 1988 GMC 5.7 engine. almost the same problem, but it is prevalent at idle. Running along is fine, but I notice the voltage gauge is right on the mark at 14 volts. Usually when running right it is the width of the needle about 14 volts. Here goes the problem. Often at an idle, the idle goes bad and I notice the voltmeter is now very low (12v approx) Racing the engine a bit the voltage comes back and the engine runs normal. I believe the lower voltage sends error signals to the TBI injection pulse via the computer. This racing the engine usually just comes back to 14, not a tiny bit higher. I tore into it the other night looking for corroded connections which could provide a voltage drop. To aggravate the condition, I disconnected the battery after starting and put my simpson 260 on the terminals. Noticed slighly more than 12 v. Putting on the headlights stalled the engine and when reconnecting the battery terminal and restarting I now have a definite low voltage. I am suspect of the alternator, but not certian. It is a rebuilt a couple years old, the battery is not quite a year old. Started it today after putting back all the cleaned cables and connections to the master terminal block no improvement. unplugged the field terminal to the alternator and it gave me the immediate low 12v indication. Be checking the master body connector and fuse connections now. Good luck Gary and any one else have any info?
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The problems on my 1988 v6 4.3 turned out to be a very eratic fuel pump that was not very old but I acually got a warrantee on that, but not the labor of course. The other thing I might pass on is that a long time ago a used engine was installed by a local garage and they did not put the braces back on the alternator or the belt tensioner there are 3 braces on the alternator to the manifold and one on the belt tensioner to the manifold. I am thinking all the shaking was cause the alternators to fail early (replaced that twice) anyway the shaking finally broke the metal flange that holds these parts in place in front of the motor, replaced that and that is a job.
Finally got 2 of the braces on the alternator from gm dealer but the long one on the alternator was discontinued and so was the one on the belt tensioner, been trying to get these from salvage yard, no luck yet.
The other porblem was finding out the throttle shaft on the TBI was a little loose so I took a can of either with a extended tip and every time I spayed that right on the loose shaft the motor would pick up speed a little, so I found one that was tight and solved that problem, the vacumn leak would cause the motor to run very fast at Idle.
Forgot to mention that the voltage was low on the alternator so that was changed along with the battery, but I think the shaking may have caused it to fail early.
Don't know if this would help you solve your problems I am just a do it yourself guy.
Good Luck
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