Bucks or stutters while under load

[jrhende6]

Replaced plugs, rotor, cap, timing chain and fuel injectors.

Set timing to 10 BTDC, calibrated TPS to 1V and did the TV pressure adjustment using the easy method.

Car runs smooth but bucks or stutters at various speeds and loads. A perfect example is when driving on level highway at 65MPH she is smooth. But when grade changes to a slight grade the car begins to buck/stutter/jerk.

Any ideas?

[87GrandMarq]

If you have an analog volt meter check the tps full sweep. Also check all your grounds.


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[gadget73]

are your plug wires routed properly? If you have the 7 and 8 wires run right next to one another it can cross-fire and do this. Those want to be spaced apart as much as possible.

[jrhende6]

are your plug wires routed properly? If you have the 7 and 8 wires run right next to one another it can cross-fire and do this. Those want to be spaced apart as much as possible.

Amazing. That helped a lot. Never thought it could happen. Inductance.

Now there is a very faint stutter and she idles rough. May be I'll go after codes now.

[jrhende6]

Replacing spark plug wires (which weren't old) with Motocraft ones fixed rough idle. Before this I tried a new TPS and nothing changed. Did the sweep test beforehand and saw no dead spots. Full scale voltage was in 3V range which I wondered about and that is why I just tried a new one. Returned the new TPS. Still stumbles around 45 MPH with new wires. I didn't use wire separators cuz I just can't see why that would help.

Guess I'll do the in the dark spark test and see if there are any stray sparks between wires and between wires and ground. Will do with someone reviving engine.

[Kodachrome Wolf]

Replacing spark plug wires (which weren't old) with Motocraft ones fixed rough idle. Before this I tried a new TPS and nothing changed. Did the sweep test beforehand and saw no dead spots. Full scale voltage was in 3V range which I wondered about and that is why I just tried a new one. Returned the new TPS. Still stumbles around 45 MPH with new wires. I didn't use wire separators cuz I just can't see why that would help.

Guess I'll do the in the dark spark test and see if there are any stray sparks between wires and between wires and ground. Will do with someone reviving engine.

When you say full voltage range was like 3V, is it reading 3ish at wide open? I had that issue where you could set the TPS correctly for closed throttle (like .9V) but it maxed out at like 3.2V and never went WOT. Didn’t have any dead spots, but the sensor was not working correctly for the specified voltage sweep. Swapped it for a new one and it was properly ranged from .9V closed up to 4.3V wide open. Drove noticeably better.


FWIW, I use spark plug wire separators not just to keep things organized, but to keep any prone-to-crossfire wires away from each other. Myself and others have posted the desired routing method off the cap and how Ford likes them routed.

[gadget73]

I have experienced cars that did not like new, aftermarket wires. Not the faintest clue why, its not like the Motorcraft ones look especially fancy or unique, but they do work. Not expensive either which is great.

[jrhende6]

When you say full voltage range was like 3V, is it reading 3ish at wide open? I had that issue where you could set the TPS correctly for closed throttle (like .9V) but it maxed out at like 3.2V and never went WOT. Didn’t have any dead spots, but the sensor was not working correctly for the specified voltage sweep. Swapped it for a new one and it was properly ranged from .9V closed up to 4.3V wide open. Drove noticeably better.

Yea like 3.4V WOT. Seemed pretty linear throughout with no flat spots. There are 3 wires. Verified the voltage between the signal and the ground wire and the signal and the chassis. No difference. The other wire is the reference and it read ~5V. Saw someone else on the internet say that some ford TPS max out at like 3.5V. Nonetheless, tried a new different TPS and the car did not run any different.

Maybe the bad plug wires covered up an issue. Am not sure. I'll keep it in mind going forward.

Thanks.

[jrhende6]

FWIW, I use spark plug wire separators not just to keep things organized, but to keep any prone-to-crossfire wires away from each other. Myself and others have posted the desired routing method off the cap and how Ford likes them routed.

Yes I've seen the TSB. 7 & 8 wire routing did make a difference. I'll do the spark test in the dark thing and reroute and use separators if I find anything.

Thank you.

[jrhende6]

I have experienced cars that did not like new, aftermarket wires. Not the faintest clue why, its not like the Motorcraft ones look especially fancy or unique, but they do work. Not expensive either which is great.

Yep $37 off of eBay. Not bad.