1990 GMC S15 I cant be far from finding the issue. Not muc

CISCOVOICEGUY

MEMBER
1990 GMC S15
4 CYL
2WD
MANUAL
19,000 MILES

1990 GM S15 2.5L TBI 700 Manual
Engine rebuilt 8 mo ago and running good until now.

ISSUE:
herky jerky under regular driving, loss of power, porpoising, erratic idle

Latest experience:
grounded the OBD1 ground wire A and turned distributor. Vehicle ran well for 10 mintues or so.
Seemed like a new truck.
Shut down and came back 2 days later.
Vehicle wouldnt hardly start and went back to same as issue above.

Replaced:
Fuel Filter
cleaned gas tank and replaced fuel
new muffler
new IAC
new EGR
new Plug Wires
New plugs
replaced TBI gasket

Next item to do
Use timing light and lock down distributor

Any suggestions are appreciated.
What should I do if the setting of the timing doesnt correct the issue.

I appreciate help.

Possible ECM?
Is there somethign the ECM could lose causing this?

Thanks

1 Reply

HMAC300

MECHANIC
48,601 POSTS

First thing you do is see if there are any codes stored in the computer. Then if there are as you have messed with everything, clear the codes by pullling the fuse for 30 seconds. Then drive the truck and see if any other ones come up. If this is a 2.5L which I think it may be, they hd problems with the reluctor inside the distributor cracking. Which would give you a problem similar to what you describe. But in order tofix this you need to get another distributor. You would need a magnifying glass to look at the distributor for the crack and still may not see it. Also check the vacuum hose to the MAP sensor as it may be collapsing. If it is soft replace it anyhow. Then put a vacuum guage on the intake and see what your vacuum is. If it's around 15" it may be the converter is plugged.