Idle not dropping to base when coolant up to temp

[ulhpilot]

'92 just upgraded to 130 gpm mods (Kennedy MFI kit). Starts right up and idles at ~ 1000 to 1100 RPM.
After reaching normal operating temp engine never drops down to base RPM. I wondering if the shop might have missed something when they installed the cooling kit. I know the cold advance solenoid will keep the engine from high idle when cold, but this is the opposite.

Also, when troubleshooting my '92 from now on, will I have to act like it's actually a later ('97-) model since it's now got all the later hardware? I looked at the '97 cooling circuit and it looks like it doesn't have the same temp sensors.

Thanks
Mick

[Robyn]

The Cold advance solenoid is in parallel with the fast idle solenoid.

Check the wire going to the fast idle solenoid and see if it has 12 volts.

If it does there is an issue.

[arveetek]

'

Also, when troubleshooting my '92 from now on, will I have to act like it's actually a later ('97-) model since it's now got all the later hardware? I looked at the '97 cooling circuit and it looks like it doesn't have the same temp sensors.

Thanks
Mick

No, since your 1992 has a mechanical fuel injection pump, and the 1994 and later models have electronic injection. Completely different animals with different wiring. The only thing that has changed on your upgrade is the physical location of the throttle cable, and possibly the high idle solenoid, due to the new location of the outlet on the thermostat housing.

Casey

[ulhpilot]

The Cold advance solenoid is in parallel with the fast idle solenoid.

Check the wire going to the fast idle solenoid and see if it has 12 volts.

If it does there is an issue.

Thanks for the reply Robyn.

I only looked at it for a minute and the only thing I really had time to do was pull the lead going to the fast idle solenoid and the engine kept running at fast idle. Guess I should have mentioned that in the OP.

So if I understand you correctly the +12 VDC is what energizes the solenoid (duh) and I've removed the source of the voltage and the solenoid is staying energized, a ground keeps it de-energized (duh part 2). And since there is only 1 wire going to the fast idle solenoid according to my service manual, the solenoid itself must be grounded. So either the solenoid is isolated from ground or is just stuck in the energized state.

OR, could the repositioning of the throttle cable bracket have caused a problem?

Well I hope it's that simple. The worst part is that I can't get back to it until Monday morning, gosh dang it.

[ulhpilot]

No, since your 1992 has a mechanical fuel injection pump, and the 1994 and later models have electronic injection. Completely different animals with different wiring. The only thing that has changed on your upgrade is the physical location of the throttle cable, and possibly the high idle solenoid, due to the new location of the outlet on the thermostat housing.

Casey
Thanks for the reply Casey. That's a killer rig you've got.

I understand the MFI vs EFI deal. When I got home yesterday morning I broke out my 1992 service manual and went to the diesel injection and cooling sections to check the whole cold advance/fast idle circuit because I had changed the cold advanced temp switch a long time ago on my OEM setup:

http://www.thedieselpageforums.com/tdpforum/showthread.php?p=25450#post25450

And from what I researched before doing the cooling mod was that the kit mimics the '97+ cooling setup. So I was sort of stumped when I looked at the '97 injection/cooling circuit (best I could find on the internet), I couldn't find the cold advance solenoid temp switch like my '92 had. I haven't had a chance to look at the installation notes for the cooling kit since it was installed by the shop working on my truck. So I don't know if it's a hybrid between the two ('92-'93 and '97+) or works the same as the original OEM setup.

Again, Monday I will have a lot better idea of what is going on.

Mick

[Robyn]

The electronics are all together different on the 97

The IP IS ALL FLY BY WIRE and the idle speed is controlled by the ECM.

The 92 has some ECM controls for The glow circuit, tranny (if auto) and a few others.


I suspect that the throttle cable and bracket is the issue.

The positioning of the new bracket is critical to allow the cable to work properly.

There is also a manual STOP SCREW on the IP throttle arm.

Make sure that the issue is not just that the screw may have been messed with.


The issue is simple for sure.

Bracket not quite right causing cable to hold throttle open ???

There should be an adjustable thimble on the cable where it fastens to the bracket.

Possibly an adjustment will allow the throttle to close properly.


Good luck

[arveetek]

Thanks for the reply Casey. That's a killer rig you've got.

Thank you sir! I've owned her since 2005, and she's been very reliable for me.


So I was sort of stumped when I looked at the '97 injection/cooling circuit (best I could find on the internet), I couldn't find the cold advance solenoid temp switch like my '92 had. I haven't had a chance to look at the installation notes for the cooling kit since it was installed by the shop working on my truck. So I don't know if it's a hybrid between the two ('92-'93 and '97+) or works the same as the original OEM setup.

Mick

Yup, totally different animals. There is no throttle cable, high idle solenoid, switch, etc. on the EFI systems. The idle and RPM is all controlled by computer. Sounds like you have a mechanical/physical issue, probably related to whatever mods were needed to fit the new style thermostat housing on, which takes up the same physical space where the throttle cable is supposed to go on the MFI systems. So a new throttle bracket (or modifications to the existing one) was needed, which means it's very likely the throttle is not returning all the way to idle properly.

Casey