'91 Ex. surging when accellerating...Help!

[clover]

I have a '91 Explorer 2wd. When I'm taking off and run through the gears, I feel a "miss" or surging effect. But when it's set on cruise control or there isn't any accelleration, the engine seems to be running smoothly. In 5th gear (I have a manual transmission, by the way) when I approach a hill, the same scenario happens, missing or surging until I peak the hill and level off on accelleration.

I cleaned the MAF and I have tightened the intake manifold bolts, which improved my gas mileage from 20 mpg to 24 mpg (highway driving). I have new spark plugs and gap'd them to factory specs. Do I need new spark plug wires or do I need a computer diagnosic run?

Thanks for the help!

Chris

 

[Bashman]

I had the same problem with the '93. I changed the wires and haven't had a problem since!

 

[Bwana Bob]

My '91 just started doing the same thing! I thought it was the crummy reformulated gas that we have to burn in the winter!
Please let me know what you find.

Thanks.

 

[clover]

I think I'll try changing the wires. I haven't done that since I've owned the vehicle. I bought it with 76000 on it in 2000 and it has 99000 on it now. I don't know when or if the previous owner had ever changed them. It wouldn't be a waste of money anyway. Thanks for your advice!

Chris

 

[TDG]

This could also be a weak cylinder. You may want to consider doing a compression check if you have the equipment and time.

Not to be the bearer of bad news but the early (90TM) 4.0 heads are prone to cracking which can cause this and some other interesting things. Has the engine overheated recently?

How are things in the world of fuel delivery? When was the last time the fuel filter was changed? FPR? Fuel pump?

On the ignition side there really isnt much that can go wrong except the plugs and wires. I have yet to hear of an ignition module failing although it could happen.

Tim

 

[clover]

TDG,

My first engine was the victim of the notorious cracked head. It did overheat, and so I put a '94 Ranger 4.0 V6 engine in it and beefed up the radiator for cooling. I also put a lower tempreture thermostat in it. I know that this decreases fuel efficiency, but I would rather cool the engine than squeeze a few more mpg's out of the gallon. Besides, I am getting 24 mpg highway.

I have never changed the fuel filter and I don't know when it was changed last. I just changed the Fuel Pump Relay, and the fuel pump seems to be working.

This morning there was no "surging" on my way to work, which baffled me. I had a Nissan 300ZX one time in which the wires appeared to be ok, but there was a dead miss. I changed the wires and it solved the problem. However, this missing is not rhythmical as the 300ZX was, and it is only during accellerating that I experience the missing/surging. On Sunday when it was like 9 degrees, I was driving in the ice to Tulsa between 15mph and 40mph and my check engine light came on for a while and went off after a while. It did this about 3 times during the trip. I then left for Louisiana and got 15mpg on the trip there highway driving. I tightened the intake manifold bolts while I was there and got 24mpg on the return trip. Of course it was in the 60's on the return trip. I didn't know if my O2 sensors were sending a bad reading to my computer, causing it to send a bad fuel/air mixture and cause the surging/missing or if it is the wires. Idling is fine and so is straight driving with the cruise control on, but man, once you depress the accellerator, you can feel the missing. Would I still be getting 24mpg if the O2 sensors were malfunctioning or the computer was sending a bad mixture?

Chris

 

[stroud13]

You might also check your vacuum tree and lines. I leak there can cause a miss and poor running, especially under a load.

 

[clover]

Problem Solved!

The problem is solved! I decided to start by changing out the sparkplug wires. I bought Bosch plug wires from AutoZone and when I started unplugging the wires from the coilpack/distributor thing (sorry for the ignorance of the precise term) and the metal piece that is supposed to make contact with the coilpack/distributor thing was corroded and blue and had disappeared! I looked into the hole to see if it had broken off but there was no sign. It had simply corroded. I installed the new wires and problem solved! Man, my engine has never been so responsive to goosing the accellerator! After having tightened my intake manifold bolts and increasing my mpg to 24mpg highway and now with new wires, I am hoping that my mpg's will increase a little more! I've been getting about 75 miles per quarter tank, resulting in about 280 miles per tank. Right now I am just under 1/2 tank with 200 miles. I'm loving it! Thanks for the support!