Mechanics

F150 MISS-AFTER WARMING UP

1990 Ford F-150

Engine Mechanical problem
1990 Ford F150 V8 Two Wheel Drive Automatic 102501 miles

I have a 5.0 1990. It started having a bad miss about 6 months ago. I changed the plugs, wires, cap, rotor, coil with no change.

What it does is when starting cold it seems to run OK. I can start off and after about a mile to mile and half it then seems to start have a miss almost like a dead cylinder or something. It does not miss under full pedal and also if I keep the rpm above 2200-2400. It has now started to spark knock a little and lose power when going up hill even with the RPM up.

I thought it may be the trans as it seems to miss or maybe it was the converter bumping or something as it seemed to happen when the trans would go into OD.

I took to trans shop and they said the trans seemed fine but it had a miss.

Someone said maybe a ignition module or something.

In a nut shell if you are going down road after warmed up when it goes into OD with any kind of pull at all it starts a bad missing/jumping like motion. Only does this under load. Even when warm it runs smooth (mostly as it does have alot of miles). Is has a slight miss when reving up up but the bad miss is when driving under load, makes the truck actually bouch like with real bad vibration like in motor/trans area.

It has to be something that changes after warming up.

Any ideas?
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BIGDADDYINGA
May 2, 2009.




Is the check engine light on? Or has it been on? 02 sensors, egr come online after warm up, PCM is in closed loop, and runs rich during warm up, 02 sensor info is not used, and egr is closed in closed loop, check thos 2 out. Also look for vacuum leaks, get a can of spray throttle body cleaner, and spray around vacuum hoses and the intake manifold, if idle changes, you found a leak.

Merlin2021
May 3, 2009.
Merlin2021,

The check engine light has not been on. Is there an easy check for the 02 sensors-egr-PCM. I know what you mean looking for vacume leaks. This has got to be something simple but finding it my not be.

Thank you.

Tiny
BIGDADDYINGA
May 3, 2009.
Try unplugging the 02 sensor, this will make the ECM use a mid value, and may smooth out engine, if it does, you just replace the 02. If not let me know and we will test the ecm.

Merlin2021
May 3, 2009.
Merlin2021,

I unplugged the 02 sensor with no change. I did find a vacuum leak yesterday that I fixed but it had no effect.

The motor starts good, idles smooth, takes gas well no bogging or missing. The only time there is a problem is when the truck is going at speed for the trans to go into OD and the converter locks up, it then has a vibration almost like a drive-shaft, when it comes back out of od or at high rpm in od it does not seems to did it nearly as bad.

The trans guys told me twice the trans is fine, but with it only doing this when it goes into OD at a low RPM and when you start giving more gas it then either misses or something is virbating, I had a van that would sometimes kill a plug and with the dead cylinder it also feels the same.

I know this is long winded but this is driving me crazy. I don't have the money for a complete shop check out so I have to try to do it myself.

I appreciate your help very much.

Tiny
BIGDADDYINGA
May 4, 2009.
You are starting to loose me. Is it a misfire, or a vibration?

Merlin2021
May 5, 2009.
Sorry, it has a mis-fire that seems like a vibration as in a cylinder not firing maybe. I have a van that would sometimes kill a plug and it made a bad shaking/vibration in the motor.

I am at my wits end not knowing what else to do. Could a bad injector cause this? If so how does one check for that?

Again thank you as I know you are putting in way more time that my little $10 is worth!

Tiny
BIGDADDYINGA
May 5, 2009.
Usually if an injector isnt firing, it will run poorly even cold, but tou can try starting the engine, unplug each injector 1 at a time, the rmp should drop about 100 rpm momentarily, if this happens at each injector, they are working OK, plug the unplugged one back in and then go to the next one. You might also clean out the throttle body with throttle body spray cleaner, follow the directions on the can.

Merlin2021
May 5, 2009.
I just drove it about 25 miles. When it started (started just fine) it worked great for about a mile. Going through all the gears. While it is working ok seems to me like the converter after shifting into od is running at a little higher RMP but as soon as it goes bad, (the converter seems to go into another shift or something and then it starts making the jerking motion. On the drive over it was on a scale of 1-10 say a 8 but on the way back it was noticeably worse. It makes spark knock more on the way back and has a over all miss that you can feel continuously. On any pull it spark knocks and loses speed (just a little). When I get off the interstate I have to turn off the OD or you can't hardly drive it, keeping the RPM's up helps it.

Tiny
BIGDADDYINGA
May 5, 2009.
It sounds like a bad or dirty MAF, that's the Mass airflow sensor, located by the air filter. This one controls air/fuel mix combined with barometric pressure. Unplug it and go for a ride, if it improves, replace it. Can be out of range without setting a code.
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Merlin2021
May 5, 2009.

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