Bucking and surging w/ Check Engine Light

[quietone]

I had a similar problem. Mine bucked and surged at idle but could not notice it at higher rpms. A mechanic (not a Ford tech) suggested replacing the gas tank cap. No more bucking or surging since then. Don't know if it was the cause for sure but it seems to be doing the trick.

 

[Turkey]

What was the reason he gave you for replacing the gas cap? That would be a cheap fix anyway. I took my truck on a day trip the other day and the Check Engine light did NOT come on. However, I still got a noticeable decrease in power after driving for a while. The problem is, I am in the process of changing the Auto Hubs (to manuals of course) and rotors now so that is where the money needs to be spent. Could just sell the truck.

Canadian Turkey

 

[quietone]

he recommended changing the gas cap because of something to do with vapor recovery/pressure/or vacuum in the tank when idling. Not really sure but it seemed to help.

 

[Turkey]

Okay, I now have new plugs and wires on. Should have changed the plugs sooner - originals at 110,000 km. Broke off #4 which apparently is a common occurance (Ford Tech says this one gets almost "welded" in there). Was a pain in the ass to get broken part out. Was taking it into Ford today anyway, so I had them replace the plugs I couldn't get out (or didn't want to attempt and break). My check engine light hasn't been on for a while but still have lack of power, hesitation and excess gas mileage. Ford couldn't get any codes so problem is still unkown. Had the fuel filter changed although did not need it. All symptoms lead to a MAF problem again, although after changing it last year, the problem returned in short order. Ford thinks it could be wiring related to the MAF. Seems like many things cause the same symptoms though. O2 sensors appear okay. Ford has seen similar cases with the 4.0L - you would think they should know the problem by now.

 

[oahrens]

Cats

I don't know of any "real" tests for the cat but what happens when you floor it? Mine bogged from the start. I also had the codes for bad MAF but it was recently replaced. Remember to reset computer by disconnecting the battery for 1/2 hour then drive normally for 10-20 miles. The fuel/air mixture ratio is controller by the computer. I replaced my cat with OEM and exhaust with Flowmaster Force II at the same time and WOW...I forgot what throttle response felt like.

 

[Turkey]

Oahrens, you must have paid a fortune for the OEM cat. I think you are right - no one seems to be able to tell me how to test the cat properly. Do you know if it is possible to just put a single high flow cat on and get rid of the rest of crap. By the way, how do you like the flowmaster exhaust?

 

[oahrens]

Turkey,

Actually...My brother-in-law is a parts mgr for a Ford dealer so.....ya know. If you're gonna replace it, the concensus is to go with a hi-flow aftermarket cat.

You'll have to check the board for exhaust options on a 94. My 91 has only 1 cat.

As far as the Flowmaster Force II...I LOVE it!!! Perfect hum without being too loud but ya know it's there. Performance and mileage increases were noticable.