More engine stumble issues 4.9L (300 I-6) Help with ideas please.

[cleandan]

A while ago I asked about some stumble issues with my 1989 F-150, 300ci-FI six engine, 5spd trans. Thanks to all for the help and insight.
I went through a bunch of tests and proved issues...and things did get better as parts were replaced, but winter also set in and the truck was basically not used since last year in early winter.

Now I am driving it again (actually a friend is using it for the time being)
Stuff that has been verified as problematic and fixed.

Spark plugs, wires, cap, rotor.
Ignition module on distributor. New ECM (this is the one part that may not have been bad)
A few gaskets like throttle body to intake and others in that area.
Cleaned IAC parts, cleaned throttle body.
New MAP sensor. New EGR control...not the valve but the control. EGR valve works.
Latest was the engine temp sender that talks to the PCM. It was very lazy and slow to react....and SUPER easy to replace too.....Oh and a new radiator, which was also easy on this truck.
In the process of all this stuff I have checked contacts, cleaned chassis grounds, cleaned and greased connectors, and other items like that....and it all looks very good to be honest.

I figured there would be some corrosion or gunk on a few of the connectors, but they look really great...I cleaned them and put them back together after checking.

Anyway, the truck is back to bucking, sputtering and generally running poorly on some occasions, but not always.
The bucking is hard and immediate, like an electrical issue. Think a kid flicking a light switch on and off, not like a fuel stumble or loss of power due to fuel issues.
It starts like it should, runs through the high idle/cold functions, idles down, and generally wants to run well. It has plenty of power, great comperssion on all cyinders (range is between 152-158psi between all six cylinders) and is getting good fuel economy.

Here is the new kicker I have found, and verified.
The headlights, or at least the headlight switch, can directly induce the stumble/bucking.

I have played around with this a bit, from just started cold to an hours worth of driving around full temp. From stop light to stop light driving, to crusing down the highway.
With the headlights on the engine acts up, and will continue acting up as long as the headlights are on.
With the headlights off there are NO issues...none. The engine runs and drives VERY well.

What might be happening here?

I am wondering if there is some internal wire harness wear, or chafing, causing a "leak" between less effective insulation. Not yet a short, but enough to cause this issue.
The other is a circuit failure. I don't know the circuits, but if there is a failed diode allowing two way flow, when it is supposed to only allow one way, it may be causing a feedback issue.

Thanks for any and all useful information.
This is a crappy, old, 150,000+ mile, rusty truck...but I still want it to run properly.

[1964Fastback]

How is your battery and alternator?  Was wondering if the added electrical draw of the headlights is reducing power to the ECM or ignition.

Pat

[gregaba]

I would check the headlight relay under the hood.
It should be in a relay box somewhere on one of the inner fender wells.
We had a simular problem with a friends 300 I-6 about 20 years ago that traced to a bad-intermitic [spell ?]  bad relay.
Its worth a try and if that and the wiring checks out OK I would try a new headlight switch.
Greg

[shady]

I've had wires inside of the harness corrode to green dust. No indication from the outside. Also had the battery ground cables do the same thing. It will drive you mad. Last one I had was in the fuel pump harness between the relay and the pump. I don't know how a wire can corrode with no damage or nicks in the insulation. One was an 88 Ranger, an 87 F-150 and a 92 Ranger.

[winr1]

Is it coil on plug or single coil that plug wires plug into ??

My 2001 3.8 Mustang was startin hard and would sometimes buck, then got real hard to accerlerate

Was the waste fire coil ...was gettin a misfire code on #2 cyl..  changed plug, swapped wires.

Code went to #1 cyl ..... then back to # 2 cyl ..... I tested with a makeshift setup

Spark was comin an goin on different terminals, replaced it an runs like new

Just a thought an best wishes



Ricky.

[cleandan]

How is your battery and alternator?  Was wondering if the added electrical draw of the headlights is reducing power to the ECM or ignition.

Pat

Both the battery and the alternator are working as they should.
Battery has good reserve power (I have a load tester) and show no signs of troubles.
The alternator is charging as it should, and within the usable range.

[cleandan]

I would check the headlight relay under the hood.
It should be in a relay box somewhere on one of the inner fender wells.
We had a simular problem with a friends 300 I-6 about 20 years ago that traced to a bad-intermitic [spell ?]  bad relay.
Its worth a try and if that and the wiring checks out OK I would try a new headlight switch.
Greg

I will check this stuff this weekend. Easy enough to do.

[cleandan]

I've had wires inside of the harness corrode to green dust. No indication from the outside. Also had the battery ground cables do the same thing. It will drive you mad. Last one I had was in the fuel pump harness between the relay and the pump. I don't know how a wire can corrode with no damage or nicks in the insulation. One was an 88 Ranger, an 87 F-150 and a 92 Ranger.

How did you eventually find the troubles?

[cammerfe]

I don't know about 1989, but earlier F series trucks had all sorts of do-dads attached to the headlight switch. I had the sort of issues you describe with my '63 Effie. All became right when I replaced the switch.

Just a thought

KS

[Lowrider]

Been awhile but when I was still working I ran across more than one F150 that had similar problems to the point of not running. On the ones I worked on there was a wiring problem in the main loom coming out of the firewall on the left side near the hood hinge. Buried in the loom is a splice where 4 main battery feeds ( yellow wires) are spliced together. You could start the truck up and pull, twist and bend the loom there to see if it acts up. Or you can slice open the loom there and eyeball the connection. I've seen them both completely corroded apart to just a little green dust around the splice.

[shady]

I've had wires inside of the harness corrode to green dust. No indication from the outside. Also had the battery ground cables do the same thing. It will drive you mad. Last one I had was in the fuel pump harness between the relay and the pump. I don't know how a wire can corrode with no damage or nicks in the insulation. One was an 88 Ranger, an 87 F-150 and a 92 Ranger.

How did you eventually find the troubles?

The ground cable was a no start, still had lights so I pulled the starter and hit it with jumper cables and it spun. Re-installed it and jumped from the batt. to the engine and it started. What threw me off was the lights working. On the fuel pump, after changing it and no joy, checked and had 12v at the relay and 5v at the pump. Ran a new wire to the pump and bingo. BTW those weren't intermittent they just quit. The 88 Ranger had a very intermittent problem where it would take fits and start missing and shaking and smell of a rich converter. After changing everything I started looking at threads on forums and there were some harness troubles. I just changed out the engine harness with a junk yard one but never actually found the problem spot. A lot of connectors ( wiper motor, coil and others) were shitty over the years, but I would cut them out and hard wire those.

[HarleyJack17]

If the headlights induce it then the issue is in that circuit. Not sure with it being a '89 but the older trucks 70's-early 80's used the same design on wiring. The headlight switch actually pulled a lot of power due to design(no relay). Issues with them could effect other items in the system as well.  Also, the high beam switch can cause issues, but not as common as the electrical gremlins caused by the headlight switch. If memory serves the old trucks headlights connected in line with the charging system. One of the more heavy duty harnesses in the old trucks.
Anyway, remove the headlight switch and drive it. If it does not repeat then that singles out the issue. Remove it and it still repeats then you need to start checking the wiring. Assuming it triggering the problem is 100% spot on. Could be a bad voltage regulator, bad ground, or a hot wire feeding into ground(shorted or wrong connection made).
I would start at the switch, then(if not a one wire alternator), then the voltage regulator/starting system, then the key switch.
What type of ignition is on it?

[cleandan]

DANG IT!
Well, the headlight switch did have a direct result in the engine miss.
Lights on, miss. Lights off, no miss....but a new switch has not solved the issue.

##@!$%%%^&&&!!! em effing electrical problems....and I am good at this usually.

[runthatjunk]

Seems interesting, if you have a LOT of time to burn!

Since there is a direct correlation to the switch, maybe unplug everything on the switch and see if any voltage is backfeeding to the switch that shouldn't be?  maybe start pulling all fuses to the bare minimum for vehicle to run and see if can isolate circuit that way?  I'm just guessing.  I assume the sensors use a 5 volt ref signal, any chance that voltage gets wonky with headlights on?

Also anything that your checking voltage on I would check voltage using the actual ground wire for that component as opposed to leaving meter hooked to a chassis ground.  Obviously seeing if different with headlights on vs off.

If lots of components get 12V from the headlight switch could even unplug and maybe individually induce 12v to componenets 1 at a time from the plug.  Good luck

[Joe-JDC]

Add another ground strap from the engine to the chassis just for test purposes. Check to see if the light switch has a gasket/grommet that spaces it out from the body of the truck to keep it from grounding itself out.  Joe-JDC