Straight 6 revs way up upon start up!
 

'88 F150 4.9L - 6

Just got done today putting back together the starter (was sticking on for a couple seconds after you let go of the key)

Cleaned it up, undented the small steel cover where it was sticking.


Now it works fantastic, but just like before, engine revs up a 'lil beyond 3000RPM as soon it fires for a couple seconds, then comes down to 1500 and eventually 700 when warmed up.


It revs up over 3000 every single time you fire it up, cold or warm!

Any pointers here? Sorry, major noob to these EFI Fords....



My other '89 Straight 6 starts great just like this one, and slowlly revs up to around 1500 for warm up.

I had a 1991 GMC S-15 a few years ago rev way up like that. It was an intermittent problem, but I finally traced it back to a bad Engine Coolant Temperature sensor. I used a meter to see what it's output signal was, turns out the value equated to a temperature reading of 75 degrees below zero (-75F).

The Ford PCM relies on the ECT just like the GM truck did. I saw your other post about your truck running cool and the white smoke. I would take a look to see what the ECT sensor is giving out as a feedback signal.

Where would the ECT be located?

This should answer that question:

http://i357.photobucket.com/albums/o...orLocation.jpg

Thanks alot for the pic! I will have a look at it hopefully tomorrow and get back with results.

Mine does the same thing, it doesn't go to 3000 but maybe 2000-2500, and I have already replaced the ECT sensor and the ECU (for other reasons). Every so often it will stop doing it for a few days, then it comes back. I've kind of gotten used to it but I will be very interested what you find out.

Check for vacuum leaks with some carb cleaner, or the IAC valve may be sticking.

8 times out of 10 with a Speed density setup that has idle problems it's a vacuum leak.

Normally I would agree with that, but in this case the idle RPM appears to return to normal once the engine is warmed up. Could be a vacuum leak that seals up once the engine is up to temperature?

If it was a vacuum leak, wouldn't I hear a hissing sound? I have checked real quick for a leak and nothing.

It idles perfectlly fine, nice and smooth, just gives that huge rev every single time you fire it up.

I wouldn't bother with it if it would only do it when the engine is warmed up, but it does it all the time, even when dead cold.....I hate revving a dead cold engine!


And forgot to ask yesterday night, how do you test the ECT? Test light with key ON? or with a meter?


Today I decided to screw around with my weird electrical problem, all lights work good, but when the pull out the knob for night lights, the left turn signal stops working. Just goes on and stays on.

When the lights are off, key on, left turn signal works fine, but the roof lights and dash cluster lights flash along with it? The PO did one hellava electric work under the truck running from the fuse box, to rear harness. Even has a bunch of marrets along the wires....

Ford Fuel Injection » Engine Coolant Temperature Sensor (ECT)

Ryan has values in ohms and volts. I would just measure the voltage value when the engine is cold. That will be the dead give away if it measures out of whack.

As far as vacuum leaks go, no most of them do not exhibit a hissing noise.

Thanks alot for the link!

It is low on coolant tho.... so I guess I'll adress that before doing anything else.