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Odd surging issue


Strelok

Active Member
Joined
Oct 14, 2014
Messages
30
City
San Francisco
Vehicle Year
1990
Transmission
Manual
If I'm on the highway cruising at 50% throttle my truck is fine.
If I try and overtake, the truck surges as if I'm getting on and off the power over and over again.
It doesn't happen all the time, and I've only noticed in in 3/4/5th gear on the highway while trying to accelerate at >50% throttle.

I suspect it's a fueling issue so I replaced the filter but haven't tested it out yet.
I have a 2000mi trip coming up this weekend so want some second opinions before I disembark.

Any ideas what could cause this?
 
More then likely the filter.

Could also be a TPS.

You could check fuel pressure, but i dont know if itll show much unless you can do it at speed.
 
Okay so I replaced the filter and nothing changed.
Got 5 hours into a 17 hour road trip and my fuel pump died, I figured that must have been the issue.
Picked the truck up from the shop I left it at this morning and drove it 5 hours home, still does the surging thing occasionally.

Shop noted that my carrier bushing is shot, possibly that?
 
No.

Carrier bearing would caue a vibratio?/hum at 40 or so mph and higher.

Aa for the surging, pull codes and go from therr
 
Check the fuel pressure regulator. It could be failing and adding extra fuel.
 
Been awhile but I've actually worked on this now.

Checked the fuel pressure:
35 primed, 35 driving
Sounds okay to me

I've discovered that the surging only happens when the engine is hot, over a certain RPM. It gets worse the higher the revs get until it actually prevents the truck from accelerating and starts to backfire, so I'm thinking it's misfiring. Also, it gets way, way worse if my headlights are on.

If I turn the headlights off it'll get a lot better or even go away sometimes. If I stop for gas for 5-10 minutes it won't surge again for at least 30 minutes of driving.

Other problems that are possibly related:
New - truck is idling at 1500-2000rpm, just started doing that
Old - truck is very hard to start when hot, new starter almost stalls but then starts turning. Starts perfectly first crank when cold.
Old - brand new starter solenoid gets stuck open sometimes and I have to smack it to disengage the starter

Anyone have any idea what the **** is going on?
 
Another update, I found a bit of spring/wire stuck in the IAC that could have been causing my high idle. Appears to be a broken bit of the spring inside the intake tube.
Idle is normal but everything else is still happening.
 
I found a ground wire dangling. Other end goes to the same bolt on the frame that the battery goes to.
I couldn't find anything that it could have came from other than the block so I bolted it to the timing cover.

Could a bad block ground have caused my weird electricals?

26977
 

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