Cold Hesitation
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Laughing Gas
Joined: Feb 2015
Posts: 765
Likes: 1
Cold Hesitation
Time to pick your guys' brains again ... I've been picking up on a hesitation/bucking that occurs while accelerating. I've had this problem before and solved it (I thought). Here's when it happens: Driving before fully warmed up (less than N on temp gauge) in every gear while accelerating. The truck never dies completely and the hiccups are very brief but frequent. After the truck warms up to the normal range it seems to drive just fine, can cruise no problems and hard acceleration feels OK. I've run codes several time and the only one that comes up is 634 for the MLPS, I am fairly certain this is not the cause.
The truck has had the PCM replaced, new Motorcraft plugs several months ago, it just passed smog in April with decent numbers, coil and connector were once found bad and replaced w/ Motorcraft parts. TFI module is a little older but those usually have hot issues, right? The only thing questionable is the fuel pump(s) and distributor pickup, but it running smooth when warm makes me think the pumps are putting out enough to make it run fine. What would you guys do?
The truck has had the PCM replaced, new Motorcraft plugs several months ago, it just passed smog in April with decent numbers, coil and connector were once found bad and replaced w/ Motorcraft parts. TFI module is a little older but those usually have hot issues, right? The only thing questionable is the fuel pump(s) and distributor pickup, but it running smooth when warm makes me think the pumps are putting out enough to make it run fine. What would you guys do?
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Laughing Gas
Joined: Feb 2015
Posts: 765
Likes: 1
Bump.
Swapped out cap/rotor, I inspected the ones in there, they are 2+ years old Motorcraft ones, there was a decent amount of corrosion on both. Haven't got the issue to duplicate yet but I'm not sold that these were the cause.
Swapped out cap/rotor, I inspected the ones in there, they are 2+ years old Motorcraft ones, there was a decent amount of corrosion on both. Haven't got the issue to duplicate yet but I'm not sold that these were the cause.
Thread Starter
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Laughing Gas
Joined: Feb 2015
Posts: 765
Likes: 1
Bump. More driving, new cap/rotor no effective. Still skips out /stutters briefly after cold soaking overnight. Only things I've checked are wiring to the coil and coil resistances, getting battery voltage at coil connector, tach signal circuit works fine, the coil itself was at 8.4K ohms so I don't think its the coil either. What else should I be checking?
Fleet Mechanic
Joined: Aug 2015
Posts: 1,829
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From: Candy Mountain
I have dealt with that for most of the time I've owned my 94. It has consistently gotten better as I have addressed different issues over the years, but it was always present for the first minute/s of cold operation. I chalked it up to carbon build up in the cylinder heads and stopped chasing my tail. But, it went away when I replaced my intake manifold. So if it really bothers you and you can afford the down time I would recommend cleaning the intake manifold. The lower is probably what really matters. It also could have been a gasket leak that was solved by replacement.
It wasn't something I was trying to solve, so I can't say what specifically cured it, but it is cured. Your results may vary.
It wasn't something I was trying to solve, so I can't say what specifically cured it, but it is cured. Your results may vary.
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Laughing Gas
Joined: Feb 2015
Posts: 765
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3+ years back I actually cracked the original by accident, I had a local junkyard supply me with a replacement, it was fully cleaned at the time it was installed. More recently I ran a Seafoam intake cleaner through it and smoked the parking lot good, so if there was carbon then, I'm betting it was burned off.
New User
Joined: May 2019
Posts: 9
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I'd like to know what you find. I'm having a similar issue that's more prevalent on my 89 f250 460. Cold or warm and it comes and goes. More recently it choked out and died after I tried to drive with it cold. Took a bit to get it started and after fighting it back to the driveway it began to idle smooth and rev fine.
The only thing I found is the timing is set base at 12* but when I plug the spout in it goes up to 30. At idle. ??
The only thing I found is the timing is set base at 12* but when I plug the spout in it goes up to 30. At idle. ??
Lead Driver
Joined: Oct 2016
Posts: 6,185
Likes: 633
From: Houston/Sugar Land
I'd like to know what you find. I'm having a similar issue that's more prevalent on my 89 f250 460. Cold or warm and it comes and goes. More recently it choked out and died after I tried to drive with it cold. Took a bit to get it started and after fighting it back to the driveway it began to idle smooth and rev fine.
The only thing I found is the timing is set base at 12* but when I plug the spout in it goes up to 30. At idle. ??
The only thing I found is the timing is set base at 12* but when I plug the spout in it goes up to 30. At idle. ??
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New User
Joined: May 2019
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Da_Lariat_Chariot what is your timing at? Let me know if you come across a vac leak on your intake. I've been checking wiring connections and found I have a lot of corrosion and rust under the hood and seen a few bare connections. I'm also in the PNW... Also, heard that bad grounds cause issues so ill be checking, cleaning those up.
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Lead Driver
Joined: Oct 2016
Posts: 6,185
Likes: 633
From: Houston/Sugar Land
[QUOTE=Shane McCormick;18676451]Thanks Sandy, 30* at idle seems like a lot of timing for idle.
The PCM changes it as conditions dictate. You are fine. Actually the standard base timing should be 10*. But a lot of guys go to 12*. Sandy
The PCM changes it as conditions dictate. You are fine. Actually the standard base timing should be 10*. But a lot of guys go to 12*. Sandy
TPS codes are stored in memory.
Thread Starter
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Laughing Gas
Joined: Feb 2015
Posts: 765
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Sandy, the base timing is 10* it was just smogged and that's one of the things they check. The TPS has been replaced, I'm not sure when exactly. This feels like I'm dropping spark while driving. Drove it today and it took 10 minutes city driving to get to the freeway, it was constantly bucking during acceleration. Once the temp gauge hit the right range and got to cruise for awhile on the freeway the problem disappeared. Checked codes again at my destination and all pass, 111 both koeo and memory.
Lead Driver
Joined: Oct 2016
Posts: 6,185
Likes: 633
From: Houston/Sugar Land
Sandy, the base timing is 10* it was just smogged and that's one of the things they check. The TPS has been replaced, I'm not sure when exactly. This feels like I'm dropping spark while driving. Drove it today and it took 10 minutes city driving to get to the freeway, it was constantly bucking during acceleration. Once the temp gauge hit the right range and got to cruise for awhile on the freeway the problem disappeared. Checked codes again at my destination and all pass, 111 both koeo and memory.
https://easyautodiagnostics.com/ford...sensor-tests-1
Elder User
Joined: Jul 2011
Posts: 793
Likes: 2
From: Vernon, BC
That almost sounds like you may have an Engine Coolant Temperature (ECT) sensor going out. The one that sends the signal to the computer has two wires (If I remember correctly it's just behind and a bit to the right of the distributor when standing at the front of the truck) and the one that sends the signal to the dash gauge has one wire. I read somewhere about a resistance test to see if the sensor is good but I can't find it and I don't have the manual that gives the test procedures for it. Sorry
I hope this can help a bit.
I hope this can help a bit.
Lead Driver
Joined: Oct 2016
Posts: 6,185
Likes: 633
From: Houston/Sugar Land
Scroll down to ECT test on this info. Good possibility on this also.
https://axleaddict.com/auto-repair/C...re-Sensor-Test
https://axleaddict.com/auto-repair/C...re-Sensor-Test