Stumble/hesitation when taking off

[Ward]

Well, I've discovered a new problem with my truck. I noticed when driving it today that it will stumble/hesitate when taking off from a stop sign, but only if I come to a stop and immediately try to go. If I wait a second, it takes off just fine. It idles smooth as butter, and the CEL is not on. I replaced the IAC tonight, and it made no difference. My next guess is the EGR valve, I'll be replacing that tomorrow. If that doesn't get it, I'll check the fuel pressure at the rail. Has anyone else had this problem? Is there anything else I could check? The only other thing I can think of would be the ignition coils, is there any way to test them?

 

[1mpg]

Mines does the same exact thing at 1/4 tank of gas. Last time it did that the check engine light came on like a day later or so and the remote starter will not turn the truck on so I'm guessing it might be a fuel problem but I hope I'm wrong since I do not want to do a fuel pump job again.

 

[Ward]

I drove it to work again today, and I've noticed that it does seem to run slightly rough at low RPM, not just when taking off. I'm going to replace the EGR, and get a scan tool so I can check for any DTCs. I'm also going to get a fuel pressure gauge and check the pressure at the rail. At this point I'm thinking either a coil, fouled plug, or fuel pressure.

 

[FordandPolaris]

I would blame a COP or plug myself. Often they can run fine at idle but once you put it under load it starts to fail. Drive like that long enough and it eventually fails all together and that is when you will get your CEL and misfire code unfortunately.

 

[toms89]

I would blame a COP or plug myself. Often they can run fine at idle but once you put it under load it starts to fail. Drive like that long enough and it eventually fails all together and that is when you will get your CEL and misfire code unfortunately.

x 2

Misfire under load is very common issue with these mod motors.

Moisture in plug well, spark plug fouled or too large a gap, bad cop boot or faulty cop.

Also check for vacuum leaks and fuel pressure if you have the means.

 

[Ward]

I am now noticing that it does have a stumble under load as well. I took it on the highway, and when trying to accelerate to 60 on the onramp, it felt like it was misfiring, and felt down on power. I'm now leaning towards it being a coil or plug. I bought a new set of Autolite double platinum plugs, and ordered 8 new coils. I may replace the injectors with the newer style type 3's too while I'm at it.

 

[Ward]

Well, I found something new tonight. I was checking all of the coils for any obvious problems, and found that the #2 coil had the mounting tab broken off. It was just loosely sitting in the plug well, and flopping around. I replaced it with a new one, and the hesitation problem doesn't seem as bad as before. I'm still going to put all new plugs in it and replace all of the other coils, hopefully that will get rid of it for good.

 

[xtinc7ion]

I just fixed my hesitation issue and stop to start "missfire" issue today. I found out that my throttle body and the housing underneath it had become clogged with carbon build up. I cleaned them and it idled perfect again but it still hesitated off the line again right after. I replaced all the plugs and it doesn't do it anymore. Rough idle was caused by a P0401 code EGR Low Flow. Hope this helps.

 

[Ward]

Hmm, I may try cleaning up the TB this weekend as well. Were you getting a check engine light for the P0401 code? I still haven't gotten a check engine light at all, I'm amazed that the engine could nearly stall when taking off and not set a code.

 

[1997SCEBFEX]

I had a 'quirk' for several months, but only at certain speeds, originally thinking trans, then one day the CEL finally came on. Funny the way the algorithm(s) work to trip it.

Hope you have it narrowed down...lots of help/pointers/experience here for sure.

PanHandler.

 

[SWAGGA]

If the amount of gas in the tank affects it... fuel filter/pump...

 

[Ward]

Well, I managed to get all four drivers side plugs and coils replaced last night. I also replaced the EGR valve, and cleaned out the throttle body while I was at it. The EGR passage didn't look blocked at all, and the TB wasn't too bad considering that it's got 142K on it. A little spraying with TB/carb cleaner and the light buildup came right out of it.

I did notice that the #5 coil appeared to have been replaced at some point, it was not an OEM part. 6, 7, and 8 all had motorcraft coils though. Also, the plugs I pulled out were all motorcraft, were gapped correctly, and didn't look too bad. I'm still holding out hope that one or more of the coils is the problem, and replacing all 8 will solve my problem. I'm going to do the passenger side plugs and coils tonight after work, I'll update again once I've done that.

Also, I may have found another thing that points towards a faulty or failing coil. I noticed that when listening to AM radio (traffic and weather station), I can occasionally hear pops/clicks through the radio. When I replaced my #2 coil which was broken, the amount of pops went down quite a bit, but they're still there occasionally. I have a feeling what I'm hearing is RF interference every time a faulty coil arcs to the head.

 

[Beardskii]

Mines does the same exact thing at 1/4 tank of gas. Last time it did that the check engine light came on like a day later or so and the remote starter will not turn the truck on so I'm guessing it might be a fuel problem but I hope I'm wrong since I do not want to do a fuel pump job again.

No check engine light. However I've owned my 2000 XLT for a little over two months now with 90,000 on it and below a 1/4 tank. (probably right in the middle between the low fuel light and the 1/4) My Expy will starve for gas and then die upon takeoff unless I pump the pedal to feed her fuel furiously.

I'm not looking forward to taking out the fuel pump and cleaning the tank if that is the case.

 

[Ward]

Got the passenger side coils replaced tonight, and plugs 1, 2, and 3. Couldn't get #4 out, I could only get at it with a u-joint and extensions, and the u-joint was at too sharp an angle to work. I'll have to find one of those flexible extension things and try again, but for now the old plug will work. All of the others I removed were in good shape, so I'm assuming #4 is also in good shape.

The good news is that it seems to be fixed, and is running smooth as new now. I haven't taken it on the highway yet, but the misfire when taking off is completely gone. I'm pretty confident it was one of the coils going bad, 6 of them were motorcraft and looked very old, if not original.

I also found that someone had shoddily repaired the PCV tube elbow at the back of the intake. I'm not sure if it was causing a vacuum leak, but it could have been compounding the problem. I have temporarily fixed it with a short section of hose, I will be putting a new elbow on it tomorrow.

Hopefully this helps anyone else who is having the same problems.