Help! '91 XLT running rough during acceleration..where should I start?

[Thallarsen]

Whether cold or warmed up, I get some pretty serious stumbling during acceleration. Once I get up to speed, it smooths out somewhat, but I still sense some rough running. It always starts fine, and idles as smooth as silk - always.
Pulled the plugs, and they look even & clean. I'm not too sure about injectors, since idle is smooth. Maybe a timing advance problem? A fuel pressure regulator problem?
As far as I know, I've done the maintenance items that could lead to this:
New plugs, new wires, new fuel filter, cleaned air filter, cleaned MAF sensor, ran a few tanks of injector cleaner, checked vacuum lines, retorqued lower intake bolts..
Still, no improvement..actually seems like it's gradually gotten worse.
I guess I'll be doing a trouble code scan. But before.....
Does anybody recognize these symptoms? What should I be looking for?
Still like my Explorer, though.
Thanks-
J.P.

 

[farkum]

Go in and have the timing checked.

 

[dogfriend]

Just kind of a wild guess, but I would check your fuel pressure. Maybe your fuel pump is giving up. You should check both pressure and flow rate.

 

[TPLYNCH]

Fuel Pressure Regulator. If it's sticking, you won't get the gas you need. They crap out after a while. I'd start there.

 

[kimchee1016]

My '91 is doing the exact same thing. I've gone down the same road you're on and even replaced the o2 sensor (buy the expensive one), the TPS and the fuel pressure reg. I'm still having the problem and have become convinced it's either a leaking/sticking injector or its a timing issue. Unfortunately I was convinced each of the parts I just listed was the culprit until I installed them and nothing happened. The code scanner registers all clear. Vacuum and fuel pressure are normal. This has been messing w/me for two months and counting. Any help would be appreciated and if I solve this I'll let you know!

 

[dogfriend]

Originally posted by kimchee1016
I'm still having the problem and have become convinced it's either a leaking/sticking injector or its a timing issue. Unfortunately I was convinced each of the parts I just listed was the culprit until I installed them and nothing happened. The code scanner registers all clear. Vacuum and fuel pressure are normal. This has been messing w/me for two months and counting. Any help would be appreciated and if I solve this I'll let you know!

If you think that it is a sticking injector, you can test for this by listening to each one using a mechanics stethoscope. You will hear a clicking noise from each one as it opens and closes. If you have one that sounds different or doesn't make noise at all, its a good bet that you found a bad injector.

Also, if you have stumbling, besides checking fuel pressure, it is a good idea to check fuel flow rate as well.

If you have an ignition timing problem, you can check using a timing light. Ignition timing is controlled by the ignition control module (ICM) and the computer (PCM). See this thread for more info: Dead Link Removed