1990 4.3 hesitating

[bad69]

TIA, my 90 C-1500 starts running strange and hesitates under load. The wipers come on ocasionally when it happens, i've replaced the distribtor, computer and ignition switch. Anyone have an idea what it could be?

[AussieinNC]

Locate and clean every vehicle ground strap making sure that both the mount point and the strap itself are really clean...

Loss of grounds will drive systems crazy...

[bad69]

Thanks for the info. Cleaned or replaced all ground straps, still having issue. Only starts after it comes off cold idle and under load. SMH

[diveplane]

Originally Posted by bad69

TIA, my 90 C-1500 starts running strange and hesitates under load. The wipers come on ocasionally when it happens, i've replaced the distribtor, computer and ignition switch. Anyone have an idea what it could be?

ok for your wipers i think its possibly a bad circuit board inside the wiper housing inside engine bay mounted to drivers side firewall. i replaced mine it was a known issue with the trucks and a recall , buy the new boards at orileys.

my issue was they would not come on , the new part did the fix, can also check the wiper relay.

[diveplane]

Originally Posted by bad69

Thanks for the info. Cleaned or replaced all ground straps, still having issue. Only starts after it comes off cold idle and under load. SMH

when u say underload general driving? take off from start.

sounds like a weak spark did u replace plugs cables? could be a ignition coil going out weak output.

[andyh1956]

The very 1st thing to do on ANY GM TBI engine is to cut the ground terminals offa the wires out on the manifold back to good wire, install new terminals & then fasten them to the same stud the battery ground cable goes to on the manifold. Make sure everthing is clean! Get that one ground wire OFF the thermostat housing!

[bad69]

Moved all ground wires from manifold to cylinder head , now wont stay running when off cold idle , had rich code , replaced coolant sensor , thinking o2 or map sensor?

[speedygonzales]

Off idle problems are often a leaking EGR

[Cabnchassis]

6 or 7 common things cause these trucks to have air/fuel issues, I would suggest going through them first, but don't replace anything you can't verify to be the issue. If you're factory parts still function correctly, they're better quality than what's available to replace them.

WIth the engine running take a can of starting fluid, and spray around the intake manifold, throttle body gasket, and anything else that carries vacuum through the system.

Verify that the engine is reaching operating temperature (check the book on what it should be for your engine configuration, but anything over 180 should satisfy the PCM)

If the PCM gets information it doesn't like, it will overfuel the engine to keep operating temperature as low as possible. It will also change operating conditions based on the data it receives, making it hard to pin down symptoms at times.

Change the two TPS sensors if need be, they're difficult to test, and some of the cheapest parts in this adventure.

If you start spend to spend more money, stop, and use a multimeter and make sure all the circuits on the fuel/air distribution systems are functioning as advertised.

Common Cutter Outters
-MAP Failure
-IAC Dirty/Failed
-Throttle Body Gaskets
-Intake Manifold Gasket (Sometimes crosses over internally, difficult to diagnose in that case)
-PCV
-EGR Leaking/Clogged
-Vacuum Leaks of any sort
-That something else you should check that I can't remember right now....

These trucks had two consistent/common failures...The wiring seems to be biodegradable in many of them, and at some point all of them will have issues with 'cutting out' due to one or many of the factors I mentioned above.

[ChevyTech]

Test the fuel pressure with the engine running.

[bad69]

Changed coolant sensor, now runs better but when enginecomes off cold idle it just dies, starts right back up and dies when no throttle applied.