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Losing patience with this truck. Randomly stalls and won't start back up.

Max Attitude

Max Attitude

Typical White Person
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Alto, MI
1992 Chevy 1500 4x4, 5 speed manual with swapped in TBI 350. (used to have a 4.3 v6).

Been having problems with this truck I bought for a beater a couple months ago. The latest thing is it won't start. I just replaced the fuel pump and sending unit last night. Started right up today and drove it. Went about 5 miles and then it started running like crap. I had to keep it in the upper rpms to keep it running. Pulled in the gas station and put some fuel in because it was somewhat low and after that it wouldn't start again. Ran battery dead and got a jump from my friend.....got it started with starting fluid...ran rough at first then smoothed out. Moved from the gas station to the grocery store parking lot where my wife was shopping, got the groceries in the truck, she shut the passenger door and the thing started running rough and stalled again. Trailered it home. Anyone have any ideas?
 
It does sound like a relay problem to me too.
How bout a bad ground? Have you checked them since the swap? Or maybe one got missed.
but another item..............
Did you change the fuel pump??? I think the v-6 pumps where smaller than the v-8's. (PSI and volume) Not 100% but it might be worth a call to parts store to check part numbers.
 
The TBI pump is the same for a V-6 or V-8, but the 94-95 454 pump is the prefferred pump to put in. Also it could be a bad ECM as it sits behind teh glove box and they do go bad every once in awhile. Could also be the OPS as the TBI engines used the OPS to trigger the fuel pump as a back-up for the ECM triggerred signal to the relay. And a bad ignition module in the distributor can cause teh ECm to not fire the injectors as it gets an amplified signal from the module to the ECm of the pick-up in the distributor.
 
The truck has new grounds to the block and frame as it had starting issues before. The pumps are the same as THEFERMANATOR said for the 4.3 and 5.7. The truck also has new distributor cap ,rotor, plugs, and wires. Last night the truck started right up....drove up and down the road a half mile 3 times. Ran perfect. :dunno:

My buddy mentioned the coolant temp sensor...could that cause this?
 
Check fusible links to the ECM from the main junction block for fatigue failure. Wiggle test. DO the same for the distributor wires. Pop the ign cap and check for an oil leak, loose magnet, etc.

Fuel pumps ALWAYS get a new relay as the failing motor can burn the connector at the pump and usually take the relay with them. Just because you got a new fuel pump doesn't mean it is any good.

Don't throw parts at it unless the computer is scanned and the ecm temp sensor is out of cal. Cleaning the contacts can fix it. Is it smoking black aka flooding? Any codes in the computer?

You tried the clear flood mode of cranking with foot on floor?

Not running at low RPM sounds like a vacuum leak or sticking open EGR. You use more fuel at higher RPM.

EGR failures are a bitch when the backpressure valve fails and allows the EGR valve to go wide open the second it gets vacuum - just off idle. They are intermittent failures and can go 5000 miles between episodes. I had flames poping back through the TBI when mine failed at the dealer and it started working fine - no clue. Till I watched episode 3 in the driveway and powerbraking had it flop wide open just off idle and the engine threw a fit. The EGR is supposed to open a specific percent by exhaust backpressure and be controlled by this. The vac signal just enables EGR function.

Electric EGR used on CA 1993 units and 1994 on up can stick open as well as vacuum units and cause a no start until you floor it.

Kitty failure plugging the exhaust?
 
No cat on the truck.

Thought it was the fuel pump because before all of this the truck wouldn't start at all sometimes. I hit the fuel tank with a hammer and it started right up....so I replaced the pump....only $55. The old on has burn marks near the wiring but if I hook it up to a battery it turns on fine.

Now the truck fires right up just fine until it stalls then it won't start again.

The plugs, cap, and rotor all had to be done anyway.

Is there a way to bypass the egr or test it? The service engine soon light doesn't seem to work. We tried pulling codes manually but the light never flashed.

Drove the truck again last night. Close to the same distance where it stalled the other day....it did it again but I coasted into my buddies driveway this time. Ran battery dead trying to start it again. Hooked jumper cables up to buddy's truck and once the battery had enough juice again I got it started by holding the gas to the floor. I had to continually rev it to keep it running and it was not running on all 8 cylinders. Sounded like a derby car running like crap. It smoothed out and I drove it home....as I was pulling into my driveway it stalled again.


Thanks for all the help so far.
 
We unplugged the wire that tells the computer to advance the timing last night (Not sure of the correct name). I drove it again tonight...only a couple miles this time but it ran for probably a half hour. When I started it I had to rev it a little to keep it running for a minute otherwise it would have idled too low and died. Once at a steady idle I dove it to a friends house a mile away. When I got there it idled for about 15 minutes at 1000 rpms. Drove it home with no problems. Tomorrow night we are going to check timing with a timing light.
 
Could also be a bad knock module as it controls the timing retard on an early TBI engine. Unhooking the jumper wire will turn on teh check engine light and cause the ditributor to go to it's base signal off of the pick-up coil of straight up timing. Also it takes the knock module out of the equation.
 
Timing was at 0*. Tested continuity of the knock sensor and got no reading so tomorrow I'm going to replace it.

Question though.... When I bought the new knock sensor they asked if it was for manual or auto transmission. I got the one for a manual and the price difference was $15 between the 2. Does anyone know why it would matter the trans type? I'm guessing the 5.7 was attached to an auto before hand.
 
Put in a new knock sensor and seems to run a little better but still idles high intermittently between 1200 and 2300 rpms. I went with a knock sensor for an automatic because it has to match up to the ecm. Chances are the 350 came out of a truck with an auto....just guessed though.
 
MAF sensor? I think that year has them.

Could be part of why it runs rough after a long hard start attempt is you may be fouling the plugs and it's taking a little to burn them off.
 
No MAF on this truck.

Well I tapped on the IAC with a hammer and the rpms changed so I'm thinking it's bad. My buddy has a truck with the same motor so we are gonna try swapping parts till we figure it out.
 
IAC can get deposits on it and make it sticky. I had an issue with the IAC on a '91 Lumina once. Engine would race at idle speed. Took the IAC apart and cleaned it real good. Fixed the problem.
 
With idling issues on a TBI, first thing to do is pull the throttle body and service it. There is a full gasket kit available for it that allows you to completely disassemble it and clean it out. They are known forcarboning up in teh back by teh IAC as teh PCV wil lallow oil to build-up back there and sludge up over time. Also the throttle body base gasket is famous for blowing out on them and causing all kinds of issues. And make sure and check teh IAC plug as they tend to break over time and get loose conenctions.
 
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