f150_wolf

**1992 F150, automatic transmission, 4.9 straight six.**

My check engine light comes on after driving at higher speeds (55-70 mph).

However, the engine light goes away after turning the car off and turning back on but will return once I get to highway speeds again.

I had a mechanic try and pull codes and he said that it wasn't returning anything.

Was wondering if any of you had any ideas as to what might cause this?

In the near future, I'm going to look into trying to pull the codes myself somehow just to make sure.

Thanks.

fomoco998

Your truck has to be returning codes under these circumstances.

sonnylynnvick75

did you notice it skip at any moment? like maybe a slight jump?

f150_wolf

@fomoco998. That was my thought when the mechanic said he couldn't pull any codes. I will look into doing this on my own next weekend.

@sonnylynnvick75: I don't notice any skips. The light just turns on. I don't notice anything with the oil pressure either.

Thanks for your responses.

sonnylynnvick75

my 91 5.0 did the same as your describing it started with no signs just the light coming on and no codes, then I noticed a stutter at 65 and the light came on and it progressively got worse until it would completely die and I would have to pull over and wait 5 minutes then it would crank back up. Just like you light came on then went off after the key was cycled and no codes. Ended up being a bad PIP sensor in the distributor. I replaced the distributor assembly and installed a new ICM.

BLDTruth

I had an intermittent CEL like you say - only came on after the truck warmed up and got up around 55mph. Turned out to be a dirty O2 sensor connector. It definitely threw a code into memory - 172 I believe. I replaced the O2 sensor and thought it fixed the problem but it came back. Cleaned up the dirty connector real well and it went away.

You can pick up an ODB1 code reader for about $25-30 at an auto parts store.

seschenburg

Ditto on the O2 sensor. Mine (94 5.0, auto) would run fine around town. Hit the highway or a long stretch between lights and the CEL would light up and stay on until I parked. Start her up again and no CEL until I hit a longer stretch of road. Replaced the single O2 sensor and no more CEL.

I also had some weird codes (ODB1), but none said "Replace O2 sensor." But it's a common cause of the CEL coming on. Also, check that your gas caps are seating properly.

akdoggie

Could be the O2 but it could also be a bad cat. Both will throw a code and drop the CEL when restarted. They will be hard coded into the system and not a soft code. (Soft codes don't retain in memory where hard codes are there until reset).

sdmartin65

As long as we're throwing darts, I'm guessing a small vacuum leak causing an EGR code. Might be accompanied by a purge solenoid code.

f150_wolf

Thanks everyone for the input.

I will get a ODB1 reader to see what codes I can pull.

My local autozone said that they didn't have that type of reader so they couldn't pull the codes for me.

Also, out of curiosity how many O2 sensors does a 1992 Ford F150 4.9 have? And where are they located?

Thanks.