Cold advance and high idle problems on a 93

[cutlas]

I noticed my high idle is not coming on when the engine is cold. Is this controlled by the temp switch to the left of the pump on the coolant manifold? Should the switch be open or closed when the engine is cold? What temp does it change state?
Thanks.

[john8662]

On the 93 the cold timing advance and fast idle solenoid is "switched" on via a switch that is mounted in a coolant port on the cylinder head.

It's located on the rear passenger's side head, near cylinder #8 and has two wires going on it (two prong connector).

The sender on the water crossover is for the transmission control, it reports back to the PCM of the engine temperature.

J

[JohnC]

the switch is closed when cold and opens when warm. I don't remember the exact temperature, but I recall it's over 100*F

[cutlas]

Will check today.
Thanks for the reply.

[daustin]

On my '93 the sensor in the thermostat crossover controls the trans shifting and the cold idle advance/speed. The sensor in the head is for the guage. My cold idle advance/speed didn't work until i changed the sensor in the crossover. Now it does.
Don

[Kev-o]

My fast idle on my 93 was not working so i applied 12v to it and still nuthin, I then blipped the throttle lever that the fast idle solenoid pushes on and it stayed on till i pulled off my temp. 12v. So it turns out that the solenoid was not strong enough to push the throttle ahead, put a new one on and it works fine now.

[cutlas]

I jumpered the connector on the coolant cross over. There was no effect so unless there is something else wrong as well as the sensor, this is the wrong sensor. I had 12v on one of the two wires going to the sensor. I will check in a few days and report what I fined.

[daustin]

I'll have a look in my FSM and see if there's a good diagram for that circuit. The diag proc in the FSM pointed me to that sensor, when i changed it it still didn't work until i cleaned the connector really well. You might also try applying 12v to the high idle solinoid plunger like above, it might be stuck or not working. Just a thought.
Don

[cutlas]

Good Idea about applying 12V to the solenoid as a check. I will do this when I get home tonight.

[daustin]

Last night i read through my FSM about the sensor in the water xover. I don't have a computer page-scanner, but in a nutshell it said "monitors engine temp for control of auto-trans shift points TCC lockup and cold-start ip advance,high idle" For the IP advance, touch the IP advance solinoid with 12V and see if you hear a "click". If it clicks, then the advance solinoid is working (or trying to). Same with the high idle plunger solinoid. The high idle plungers are known to stick & die as they get older. I'll see about bringing the FSM into work and scan some pages if you need them.
Don

[cutlas]

Thanks Don.
Can you tell me where the advance plunger is located on the pump?
Also what effect would a bad coolant sensor have on shifting and lockup?

[daustin]

When mine wasn't working (sensor was open all the time - thus it thought it was hot) the trans worked like it was warmed up shifting normally. When it thinks the engine is cool, it will delay the TCC lockup some. IIRC on the 4911 IP the red wire is on/off and the green wire(s) are the IP advance. Don't recall for sure the high idle plunger's location, either on the throttle bracket or whether it's in the IP advance. When i got mine, neither of those worked at all, traced through and deternimed it was the sensor/switch on the thermo housing. My temp gauge didn't work either, i replaced the 1 wire sensor in the head first and that worked then while in process of doing some other work replaced the thermo sensor/switch. I had a leak so i had the crossover off anyway, better to drain it once than make a mess. lol Let me know if you need any info from the FSM, i bought the whole set when i bought my '93 gasser new. I got the '93 6.5 dually early this year.
Don

[cutlas]

I finally got a chance to check out the truck yesterday. I have a bad coolant sensor and a bad high idle solenoid. Will order new ones today.

[daustin]

Mine seems to work ok after replacing the sensor, now i'm in "trans-swap" mode as my 4L80E crapped out. :mad: Looks like a PIA to change, bolts behind the motor look hard to get to.
Don

[cutlas]

I have replaced the sensor and see no difference in the way the truck starts. The truck starts ok (I have one broken glow plug and one old one behind the down pipe that will get changed) just no different except for a bit more noise. What should the cold start advance do?

[JohnC]

The timing advances and the idle increases. Many cold idle solenoids are not intended to be able to open the throttle, just hold it open after you step on the pedal.

The timing advance accounts for the increase in Diesel rattle. Once the engine temperature reaches 100* or so you should hear it drop out.

[cutlas]

Thanks John. I do understand what happens I just don't know why it is needed. Also I have advanced the pump about 1mm to compensate for an old timing chain and the truck runs good now. So what are the signs to watch for when your timing is to far advanced under cold start conditions?