91 GMC 5.0Distributor Question

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Iceman54
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Joined: Wed Jun 05, 2019 1:37 pm

91 GMC 5.0Distributor Question

Unread post by Iceman54 » Wed Jun 05, 2019 2:02 pm

Just reregistered back on the forum. Been superbusy on the job and house lately. Lost my password. So, now time to work on my truck. I got it from my Dad last year.. It has a new engine in it, with a rebuilt TBI, new coil, fuel pump, and all other sensors new.The distrobutor was also replaced with one of those ebay $55 specials that are all over ebay now. It ran ok for a while but is gradually idling worse as it goes. I'm looking at going with an Accel or an AC Delco (Rebuilt). Any ideas. Also no codes and all sensors and wiring has been checked.

S

 

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carriedi
Posts: 2268
Joined: Wed Apr 10, 2013 12:42 pm
Location: Oregon

Re: 91 GMC 5.0Distributor Question

Unread post by carriedi » Wed Jun 05, 2019 9:20 pm

not sure what you mean when you say the idle is getting worse. What is it doing? Idle too low? Idle rough? Stall?

If you could hook it up to a scanner you could look at your fuel trims to see if it's going rich, lean or okay. you could look at your idle air control to see if it's within a normal range and acting smoothly. How is the spray pattern out of the injectors? Is the fuel pressure within specs? (something to look at even if it is rebuilt)

How's the quality of the fuel in your area? Sometimes the ethanol content isn't what they say it is. You might want to try a fuel system cleaner. Keep that new engine clean on the inside.

you could hook it up on a 5 gas or even a 4 gas engine analyzer and see how the exhaust is coming out of the tailpipe. If it's coming out clean (less than 220 hydrocarbons and less that 1.0 CO at idle the engine is running good. (according to state emissions...)

what do you think the distributor is dong? bad pick up coil? Module? is the engine missing? If it is can you tell which cylinder or cylinders? An engine scope could look at the secondary ignition and see how each of the cylinders are firing. It could pick up on a spark plug or wire that is not firing correctly. If a cylinder is running out of fuel too soon compared to the other cylinders. Or too rich. Too high KV could show up if resistance is too high for the spark to jump. Most scopes have a test for running cylinder balance. It tests the running engine to see it they are all firing evenly. Check to see if you have any cylinders that have a lower contribution that the others.

you said that you replaced the distributor. Did you have a problem with the old one? what was that one doing?

let me know what happening and tell me if you can describe the concern you have about the distributor. And how the idle is getting worse.

Iceman54
Posts: 3
Joined: Wed Jun 05, 2019 1:37 pm

Re: 91 GMC 5.0Distributor Question

Unread post by Iceman54 » Fri Jun 07, 2019 2:56 am

Truck sat for several years under a tree and drivetrain was not maintained by previous owner. Engine has been replaced, along with about every sensor on the motor prior to me getting it. It has been to several shops, and computer checks prior to me getting it. The last item was the aftermarket ebay distributor, with a very thin base plate, which is probably why the electronic went out last summer
I've since resealed the intake manifold due to a leak and a catalytic converter after a follow-up check of exhaust. TBI rebuilt, new injectors, and fuel pump / filter replaced due to low / fluctuating pressure. New pump press was @ 13 psi and steady.
The idle problem is intermittent and has not been weather or temperature related. Wires have been checked and @ all sensor connectors have been replaced. Plugs, plug wires, IAC, TPS, EGR, Coil, Fuel Pump Relay, Coolant sensor, Exhaust sensor have all been replaced, the result of several shop computer checks in La. The only codes I have seen have been for the bad TPS and a bad ECM, which I also swapped out..

Iceman54
Posts: 3
Joined: Wed Jun 05, 2019 1:37 pm

Re: 91 GMC 5.0Distributor Question

Unread post by Iceman54 » Sun Jun 09, 2019 2:22 am

So, to continue on...stopped to get gas after work (2nd shift) and set the pump to auto fill, ignition key off. Popped hood and pulled dipstick to check oil and saw a spark as the dipstick came out of the tube. Spark was down where the tube contacts the heat tube from the exhaust manifold to the TBI air inlet. Pulled the spark plug wire away from where it contacted the dipstick tube and pulled the dipstick, no spark. Don't know why there would be any power to anything with the key off. Looks like I'll be chasing some wiring and replacing plug wires.

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carriedi
Posts: 2268
Joined: Wed Apr 10, 2013 12:42 pm
Location: Oregon

Re: 91 GMC 5.0Distributor Question

Unread post by carriedi » Tue Jun 11, 2019 3:03 am

yes, having a spark jump at the dipstick is very odd. That should all be grounded to the block around there. very strange.

you still haven't said what is wrong about your idle? It intermittently does what?

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