95 4.3L Sonoma no-start issue- need some brainpower

[duh09]

Hey guys,

I know, I know, not a Mustang blah blah, I need some help with my Sonoma.

I recently bought a beater 95 TBI 4.3L Sonoma and have begun to have a no-start issue that I cannot for the life of me figure out.

-2nd day after I bought it, the truck would not start. Hit it with a small squirt of starting fluid and it fired right and drove around fine for a couple weeks after. The truck has been sitting so I thought maybe it had some gunk in the lines, added some fuel cleaner in it and have been driving it a lot over this past weekend problem free, adding fresh gas every time it got down to 3/4 tank, no issues for nearly a week
-Went to get into it yesterday, and same issue, would not start. Came back home after work, hit it with starting fluid and it ran fine. Drove up and down the road and came home, let it idle for a few minutes. Shut it off, started right back up on its own. Let it idle for a few more minutes while checking a few things out, shut it off and tried again and no start.
-Thought fuel pump might be on its way out so bought one and when I got in it to move it to my shop today, it fired right up again. Drove it down the road and back, let it sit, shut it off. No start. Went ahead and changed the fuel pump thinking maybe it was just getting weak and not 100% done yet but no change with new pump.
-Watched TBI setup while cranking and it does not look like the injectors are spraying anything on start-up. Once started with starting fluid, fuel is very noticeable.
-Little bit of Google research pointed to possible ignition module failure. Replaced it, no change.

Some things I noticed while messing with all this:
-I'm not 100% sure the fuel pump primes when turning the key on first. The buzzer in the cab is too loud to really notice for certain by myself, but I'm pretty sure I have heard it at least a few times. The fuel pump does pump while the key is being turned and the truck is cranking over and the pump will continue to run for around 2 seconds after you stop cranking. I would think that if I had a fuel pump relay/fuse issue, the pump would not run at all.
-The cap, rotor, and well the rest of the distributor look like shit. I do not believe I have any sort of spark issue simply because it will fire up on starting fluid and runs great but if the ignition module is something that could cause a no-fuel at startup problem, then it seems like it could be a possibility.
-TBI setup does not have typical Schrader valve (WTF Chevy!?), not sure if Fuel Pressure tester at work has adapters for it or not. If we do, I will check my pressure tomorrow evening and see what's up.





tl;dr version: Stupid Chevy cranks but doesn't start. Will start on starting fluid. Runs fine once started. New fuel pump, new ignition module, no change. Ideas?

 

[duh09]

Also here's a picture of the beast, because you know you wanted to see what it looked like.

 

[lutter94]

no pic

 

[CC'S95GT]

I might tend to thing it's the fuel pump relay module.. Maybe it's sticking or the terminals are corroded and not getting a good signal to latch in.
Maybe the coil too. Not producing enough spark to fire the fuel but there's planty to fire the ether.

 

[kb1982]

Does the truck seem like it is running rich? Usually the 4.3 vortecs aren't tb injection, but multiport. They had spider stlye injection. Its the funkiest thing you will ever see, and they can be problematic. It has 6 tubes with a poppet valve on the end that injects the fuel into the runner, 1 per runner. They were also very sensitive to fuel pressure. Heres a link for a better understanding of the mutant. http://www.tomorrowstechnician.com/living-under-the-hood-diagnosing-central-port-fuel-injection/

 

[duh09]

I might tend to thing it's the fuel pump relay module.. Maybe it's sticking or the terminals are corroded and not getting a good signal to latch in.
Maybe the coil too. Not producing enough spark to fire the fuel but there's planty to fire the ether.

The terminals look fine, would think that if it was sticking, the systems would happen randomly while running or not but the problem is only when cranking. Coil is throwing bright blue spark and I'm not seeing any fuel whatsoever spraying on start-up so still leaning towards fuel/electronics over ignition.

Does the truck seem like it is running rich? Usually the 4.3 vortecs aren't tb injection, but multiport. They had spider stlye injection. Its the funkiest thing you will ever see, and they can be problematic. It has 6 tubes with a poppet valve on the end that injects the fuel into the runner, 1 per runner. They were also very sensitive to fuel pressure. Heres a link for a better understanding of the mutant. http://www.tomorrowstechnician.com/living-under-the-hood-diagnosing-central-port-fuel-injection/

The truck is 100% without a doubt a TBI setup. I bought it specifically because I will not own a faulty abortion spider injection setup after all the parts I sell for them- they all seem to take a shit eventually.




I did some talking with a very knowledgable mechanic today and he recommended throwing a noid light on it to see for sure whether or not the injectors were getting signal on startup. Light BARELY registers and can really only see it in the dark. Wasn't sure how bright it should be, so I started it on ether, and plugged it back in and was very bright flashing at idle so pretty sure I've narrowed it down to not getting signal to fire which points to ECU... Hoping I can get one from a junkyard tomorrow, otherwise I may be up shit creek unless theres something else I'm missing.

 

[kb1982]

Hoses hanging in a hot manifold wasnt GM's greatest idea. I had a 1994 Blazer when I was younger. It had some spiders leak, and trashed the engine. It was rebuilt and had that issue resolved, then the abs module went out and it would lose all the brakes. After my cousin rear ended a car with it, I ended up with it for free. Drove it for a few years after replaceing the abs module, then it crapped out again and away it went. I would check the wires and fuses that feed power to the injectors. Usually the ecm just grounds the circut, which causes the injectors to fire. Hot to the injectors, then the other wire just runs to the ecm to ground the injectors to cause them to fire. Try hooking your truck up to another vehicle with jumper cables and try starting it. It may boost the circut enough to fire the injectors.

 

[alex302]

ive had this happen here at the shop with 2 4.3L if it has the flat style distributor cap they have an internal fault. replace the cap and rotor and you should be good.. the two trucks that came here had no start i put a new cap and rotor and boom ran great

 

[Z06killinsbf]

Do a search on s10forum.com for this issue. I know a lot of the fuel pump related issues are tied to a bad/faulty ground wire which is in the tail light harness somehow.