Stumbling / hesitating 4.0 OHV

[David in NC]

My son complains that his '97 XLT 4.0 OHV occasionally stumbles or hesitates when he starts off at a light. It doesn't stall or die; it just doesn't jump when he gives it the gas. Then, about a half a second later, it goes and drives normally.

It's got about 120k on it and we've had it for over 30k of those miles. We've had the plugs and wires changed and the timing cover gasket and head gaskets changed and replaced the egr solenoid, but no other engine matters. Has anyone else experienced anything like this? I might run some Techron through it while I ponder the problem. Suggestions? TIA

 

[sdaviddr]

I have the same problem with my 97 sport.About 1 month ago,I put a bottle of STP fuel injector/system cleaner in the tank and couple days later the problems started.
1.Its takes a second or two longer to start.
2.slight stumbling & hesitation taking off from a light
I'm going to change my fuel filter(soon as I buy a tool thats works),spark plugs(when my budget allows it)
Hope someone has a answer to our problem.

 

[Cobraguy]

Check your fuel pressures. What is going on there when this happens? Do we have a regulator that isn't raising the pressures when he takes off? (creating a momentary lean condition) Fuel filter not been changed in years? Pump weak?

See if your EGR is opening too soon or is slightly open. In the days of old, we used to have to put vacuum restrictors in the lines to stop that from happening. This is the exact symptom we had from that.

If that's good, then check the TPS for smooth readings. Make sure there isn't a dead spot in it. Watch your meter extremely carefully for any jumps while slowly sweeping the throttle. This may need to be done by a shop if you don't have the tools.

There are lots of other things to check like vacuum leaks, etc. But this is a start.

 

[96eb96]

My son complains that his '97 XLT 4.0 OHV occasionally stumbles or hesitates when he starts off at a light. It doesn't stall or die; it just doesn't jump when he gives it the gas. Then, about a half a second later, it goes and drives normally.

It's got about 120k on it and we've had it for over 30k of those miles. We've had the plugs and wires changed and the timing cover gasket and head gaskets changed and replaced the egr solenoid, but no other engine matters. Has anyone else experienced anything like this? I might run some Techron through it while I ponder the problem. Suggestions? TIA

Clean the MAF sensor. It is near the air filter. You can find many links online how to do that. A dirty one will cause that hesitation. I would do that before doing ANYTHING else.

 

[TB2K]

I agree with the maf sensor cleaning, I just cleaned mine (VERY VERY dirty) and made a huge improvment, while I was at it I also cleaned the other sensor in the intake tube just before the bend into the TB (IAT sensor maybe?). now I get no hesitation at all.