I did 12 hours of hard wheeling on Saturday. Driving home I started to notice this new problem and has become worse over the past couple of days. Before the trip, I was not having these symptoms.

When the engine is cold, at partial throttle, the engine hesitates between 2 and 3k rpm then at 3 I get a quick surge only for a second then it runs normally. If I'm really heavy on the gas, it doesn't seem to happen and when she's warm it doesn't for the most part but has once or twice.

Changed the plugs but didn't help. Any ideas?

 

Not sure but I am having the same problem. I think I read one thread where it might be a bad o2 sensor, but I am not sure.

 

what type of engine is it?

 

could be a vacuum leak, TPS sensor just slightly out of adjustment, O2 sensor not heating up properly (looks like you've got an 89+ truck there so should have heated O2 sensors), possibly coolant temp sensor (to the ECU) slightly out of range, fuel pressure not repsonding properly- maybe fuel filter.

 

3.0 '92 4x4

 

Lots of suggestions - thanks.

How would you go about pinning it down? I don't just want to start throwing parts at it an hoping.

 

I had the same problem.. i started with new plugs wires rotor and cap.. problem was solved

 

Throwing any codes for you?

 

check for vacuum leaks
replace the fuel filter
check the tps: http://www.4crawler.com/4x4/CheapTricks/TPS/index.shtml

coolant temp sensor and O2 are a little more involved, but probably okay if you're not getting codes.

 

No codes. I'll try a few things out and let you know. Thanks for the suggestions.

 

Could you possibly have cracked or crushed your cat? I had a cracked cat and it caused "hesitation" at low rpm's (under 3k) and then kind of "kicked in" once over 3k rpms. Once I pulled the cat the problem was gone no hesitation.

 

There is a diagnostic mode also that may allow you to catch the bugger

 

Do you have some more info on that?

 

Nevermind, I found out about how to do the diagnosis with the jumper wire. Everything is fine there. I get the constantly flashing CEL.

I replaced the cap and rotor. The old ones were in bad shape.

Went for a quick drive. The problem has lessened but still there.

I don't hear any vacuum leak so I don't think thats going to be it.

Now that I have been around the truck while idling, I noticed a puffing sound coming at random intervals from the tailpipe. 1 or 2 "puffs" every second or so. Doesn't sound right and they match the hesitation sounds of the engine.

Not sure if that would help narrow it down at all.

Also, a buddy suggested EGR valve. How do you test them to check?

 

Most likely not an EGR (i could be wrong though). In the FSM (factory service manual) symptoms for "surging" suggest a faulty fuel pressure regulator as the first priority for checking/replacing. I have surging while i drive on the freeway in OD and i'm about to replace it. Next would probably be an O2 sensor. Be aware that O2 sensors don't operate during engine warm up and wide open throttle, so if your problem occurs during those times too it's not an O2 sensor

 

Can you tell me where to get my hands on an FSM. I'm sure there's one on the net.

FPR sounds like a good bet too. Hadn't considered that. Can you tell me where it is and if its possible to test it since a new one's $150 I want to make sure first. The Haynes manual has no mention of it.

O2 is something that I want to do anyway, so thats next on the list.

I was talking with a guy last night who has a Chev. He was getting random sputtering and hesitation just like me. He said it was his battery on the way out, it affects the fuel injection if there is not enough juice there. Does the same thing occur on our trucks? I know my battery is on its last legs and I need a new one for the winter. I left my lights on for 2 minutes the other day and it almost didn't start!!!

 

Funny thing is that my surging/hesitation problem took care of itself....wtf? I had the problem for 2 days then all of sudden went away. Weird stuff. Anyways the link to the FSM is...
http://www.ncttora.com/fsm/1990-1995...es/repair.html
good luck. if the link doesn't work then go back to the forum and you will see the "sticky" link for the service manual. Good luck.

As far as location of the FPR, when standing in front of your truck looking at the engine, it's located just to the left of the front end of your driver side valve cover, it's about 1" in diameter and sits on top of your fuel rail. It will have a tiny vacuum hose going into it along with another slightly larger fuel hose.