Rough Idle + missing (random)

[mnewman]

I wasn't sure how to search for this. Everything that came up didn't really sound like what was happening. The truck runs great ('88 5spd) and then, all of a sudden, it will start missing badly, it will barely idle and as one would think, has no power. Then anywhere from 5 sections to 5 minutes later it just clears up. Its like someone if flipping a switch. Seems to only happen after it's warmed up a bit. It's actually only stalled on me once but fired right back up. I can't detect a pattern other than it's getting worse. Not sure if it's related to the cooler / damp conditions. I can smell the fuel when it starts acting up so I feel like it's getting plenty.

Does this sound like a TFI module even though it rarely dies completely and always restarts? Plugs, wires, cap, rotor, ECT and idle air control were all replaced within 1000 miles.

 

[RonD]

Yes, it does sound like TFI module, they would act up when warmed up that was the common parameter, warmed up, if problem NEVER occurs cold then TFI would be first stop
And the TFI modules were just a known issue over the years they were used

It could also be a computer issue, but warmed up and random would be a stretch for computer issue, hard to say at this point

 

[mnewman]

Thanks Ron. I will see if I have a spare on the parts truck and go from there.

 

[mnewman]

No go on the TFI module but the one I swapped onto the truck was used. Exact same behavior. It used to be random and cleared up quickly. Now it clears up for a few seconds and goes back to sputtering, it's bad enough I can't drive the truck anymore. Seems like as soon as the truck gets out of the cold start loop it starts acting up. I will have a video up this even that shows how it's running.

 

[mnewman]

Here is a link if anyone is interested in the test drive after the TFI swap to see what it's doing. Not sure what else to look at...

EDIT: Read the BII thread in here. I am going to track down a fuel pressure tester and see what I have. Sounds pretty similar.

 

[JerryC]

I had one of the connectors get loose on the high pressure pump (on the frame rail under the driver seat) and it did something similar.
Crawl under the truck and check them out. I barely touched the wire and it fell off the pump.

 

[mnewman]

Good call. I will check the connections. I borrowed a fuel pressure tester and when I start the truck it sits at zero for several minutes before slowly moving up to 32 psi. So I tested it on my BII which did the same thing (but runs ok). So I tested it on another '88 with a 2.9 and it jumped to 30 psi immediately. Looks like the high pressure pump on my two trucks is bad?

 

[mnewman]

Unless there are other opinions I guess I will throw a high pressure fuel pump at it. I gotta get this thing fixed. Just seems weird that this thing would run at all with zero fuel pressure. I feel like I did something wrong with the tester.

 

[mnewman]

Still chasing this... No codes. Took apart the fuel reservoir thinking there was filter in it (orielly sold me one??) but no filter was in there. Should there be one or is that older models?

 

[RonD]

No, no filter in the reservoir on most, in the two pump system it was just there to keep high pressure pump primed

 

[mnewman]

Ok, so back at it. Not fixed yet. Both fuel pumps have been replaced and filter. I have good fuel pressure now. Seems like its running better but will still start missing badly and clear up (its like you're flipping a switch). The running better (by running better I mean it doesn't have as many bad spells) could be because it's 30 degrees out. I don't know. Does anyone have any thoughts? New computer? Burn it down? I'm about to end of what I'm able to do.

No codes

Parts replaced in the last 500 miles
Plugs and wires
Cap and rotor
TPS
ECT
Swapped the TFI module off my parts truck (no change what so ever)
High pressure fuel pump
In tank fuel pump
Fuel filter
Water pump and hoses

 

[RonD]

You can pull the computer and have a look inside

The 2 or 3 capacitors can leak after 20+ years and cause all sorts of running issues, under $5 for parts to replace these

Also check the 60-wire connector and circuit board for corrosion, the sensors all work on 5volts so even a little corrosion will change voltage enough to throw computer off

 

[mnewman]

I pulled the computer. One cap looked like it might have a but of corrosion on it but not obviously bad. 1 I have a computer from a 90 brocco 2 with a 2.9 automatic. Can I run that in my truck? Mind is a 2.9 with a 5 speed.

 

[mnewman]

Swapped in the other computer. It runs better but now has a surging issue. Wondering if it isn't the same issue just not as harsh. I pulled the codes and all I got was errors from not having an auto trans.

 

[mnewman]

In case anyone was curious. I have left the "new" computer in and the truck seems to be doing fairly well. Just random check engine lights from the computer being from an automatic rig. Although EVERY time you start it it runs for 20 seconds cuts out and comes right back then runs normally. Have no idea on that one.

Cheers.