I've got an 88 3.9l Dakota. Since I started driving it I've noticed that taking off from a light, when I first hit the pedal it accelerates smoothly for a second or two, then seems to choke, then picks back up.

Occasionally after a few minutes of driving it'll actually sputter and stall. Always when accelerating from a stop.

I've also noticed that while driving down the road, if I give it full throttle it'll sound like the engine is under heavy load and I get no acceleration or increase in rpm. Drop back to about 3/4 throttle and she's of to the races.

Any ideas? I've changed the fuel filter, done a full tune up, can't find any vacuum leaks. Not sure where to look next.

 

Check your exhaust back pressure - you may have a partially plugged exhaust with a truck this old (like mine was when I bought it ... )

Also, check your O2 sensor; again, it's age that may be getting to it.

RwP

 

O2 sensor was actually replaced last week.

I disconnected my battery on my lunch break today, double checked vacuum hoses etc. Now I'm sitting on the side of the road, thing just will not stay running, even at idle.

 

Why did you disconnect the battery? What you describe sounds like the throttle is (edit: over and under) delivering fuel randomly. Is it carb or EFI? If it's EFI the Throttle Position Sensor might be bad, fuel pumps can give trouble and it might be the wiring harness not the pump itself. Sorry that sounds like more problems to figure out.

 

I managed to limp it home.

Disconnected the battery because I read somewhere on here that it's good to reset the computer after replacing an o2 sensor.

It's throttle body injected, I've tried disconnecting the throttle position switch and it acts the same, idles down and stumbles until it cuts off completely. I can watch the throttle kicker (external equivalent to idle air control) slowly opening the throttle as it's dying down, sometimes the rpms will jump up, and it'll pull back, which usually ends up stalling, or sometimes it just keeps trying til it dies.

As to the converter, cut the exhaust just before the converter and it doesn't seem to have made any difference.

 

Hi, OK the PCU needs to have a signal from the TPS to run the motor. It tells the computer where you have the throttle. They are pretty cheap. So now that you are home check for codes. There is a lot of info on the FAQ page and one part about codes explains how to check using the key and looking at the check engine light. 12 will be the first one since you disconnected the battery, it means the battery has been disconnected with in the last 50 starts. The last one will be 55 which means code reading is over. The FAQ page link has a list of all codes. Hopefully this will tell you something helpful. I'm not sure cutting the exhaust before the O2 sensor like that will help it does need a certain amount of back pressure. There is a way to check for exhaust blockage by checking vacuum pressure I can;t remember how it is done right now. ETCG has a video on it.

 

Unfortunately I can't check codes, no scanner and the check engine light doesn't work (I already checked the bulb, and the electrical connections to the cluster look clean).

Heading grab a TPS now.

 

Try to avoid spending money until you know exactly what the problem is. Hopefully Ralph has some insight I think he has an 88.

 

After much tinkering I was pretty sure it was a fueling issue. Went on Rock Auto and found the fuel pump cheap, also found a cheap throttle position sensor so I grabbed it as well. When the parts came in I immediately installed the TPS, which made no difference at all, but for $16 I figured it was worth a shot.

Installed the fuel pump yesterday, everything went smoothly, loosened the bed bolts on the pass. side, removed the ones on the driver side, unscrewed the filler neck, and lifted/propped the bed.

Pulled the fuel lines off, pulled the vent line, and the vacuum/emissions line (I assume that's what it is?), removed the pump/sender assembly. I replaced the pump/sock no problems and re-installed the assembly in the tank.

Started reconnecting the fuel lines, Return - Check, Drain - Check, Supply - *Snap* , the plastic nipple broke off. Eff me.

Ran to the parts store and found the only epoxy that listed chemical/fuel resistance, steel filled marine epoxy. Cleaned everything up good, roughed the surfaces with a stiff steel wire brush, and applied a healthy does of epoxy to the break and made a small bead around the outside of the break. This stuff requires 15hrs to cure so I had to leave it overnight.

Got up at 4am this morning, popped the supply line onto the repaired fitting and fired it up. Ran great, no more slowly falling idle, ran nice and smooth, so I bolted the bed back down, reinstalled my bedliner, cleaned up and drove to work.

The hesitation off idle and at WOT are both completely gone! I still have a slight roughness to the idle when coming to a stop at a light, never close to cutting off, but noticeable.

If I can find a cheap tach and a timing light I'll check the timing and make sure the throttle kicker is properly adjusted.

 

After changing out the pump, don't forget to swap the fuel filter (the one on the frame!)

That sucker can cause all kinds of fueling problems also.

Do you have the manual for how to adjust the throttle kicker?

RwP