craig marshall
New Member
93 6.5 idling too high and jerks in high gear when decelerating until brakes are tapped
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93 6.5 idling too high and jerks in high gear when decelerating
- Thread starter craig marshall
- Start date
Will L.
Well-Known Member
Welcome Craig. Im drawing a blank, but there are a lot of guys here smarter than me that will help soon.
Db2 tps not set right?
Db2 tps not set right?
- Staff
- #3
As for the idling to high, sounds like your fast idle solenoid is stuck on. I believe theres a temp switch that shuts it off at around 130 degrees or so. If it's stuck on, it most likely has the cold advance stuck on as well. With awarm engine, I could see it buck with the fadt idle and cold advance on. As to stopping when you apply the brakes, the controller unlocks the converter when you apply the brakes, so thats probably why it stops. Make sure you have a good t-stat so that its com8ng up to temp. I'm not 5he m9st well versed on db2's myself either, just throwing some ideas out there.
DB2's are stupid simple.
Cold advance is easy to test: Look for the 2 wire switch in the T-Stat crossover. On a hot engine, unplug it and make sure it's "open" across the contacts. Cold engine the contacts "short". X2 on making sure the T-Stat isn't stuck open.
Simpler test: Stone cold engine turn ignition on - do not start. Open hood and manually work throttle. The Fast idle should drop and hold the throttle open. Unplug the switch in the T-Stat crossover and the throttle should drop back. Wouldn't be the first or the last time the cold advance failed and the IP (hot) idle was adjusted to cold RPM specs.
Transmission
The Service Engine Soon light will almost never come on. (I have seen it flicker due to wiring shorts around the transmission. Even when the OD planets ate a bearing and sprag clutch with an earth shattering "KABOOM!" and I no longer had OD with lots of codes: no SES light on. ) There are NO EMISSION CONTROLS THE ECM MONITORS OR CONTROLS on 1993 HD Emissions trucks! Therefore it isn't required to turn the SES light on so GM doesn't. What this means is transmission trouble codes can be present without the SES light on. GM did not make a Service Transmission Soon/Now light...
Read codes, if any, out of the ECM with a paperclip as covered in the technical reference section on here. http://www.thetruckstop.us/forum/threads/obd-i-reading-your-codes.3938/#post-47918
The TPS on the IP can be adjusted by back probing the connector to get 0.5v at hot idle. You do this after you have adjusted both the cold idle and hot idle RPM : by the book needed every 6 months. No SES if it's not adjusted properly: just harsh shifting of a limp mode.
You need to count the gears and TCC lockup. I suggest starting in 1 and moving the selector through each gear and being in OD (4th) at 35 MPH. Then take it over 45MPH to feel the TCC lock. This test makes sure everything is working allowing all 4 gears and TCC lockup. I didn't say adjusted properly, I said Working.
IMO you are not obtaining OD and have the 3rd gear manual select over run clutch on. Mis adjusted shift linkage somehow (test above can eliminate) giving you manual 3rd or TPS on the IP not indicating to the ECM you are back at idle? Regardless in manual selected 3rd gear this weak overrun clutch comes on. If the TCC is also locked when you take your foot off the throttle compression braking will overpower this clutch causing a surging feeling esp. going downhill. (If the TPS doesn't indicate "idle" to the ECM the TCC can stay locked.) Eventually (quickly) the clutch pack burns out and you get no compression braking in manual 3rd. All forward gears do not notice this fried clutch pack and work fine. This clutch pack can compression brake if and only if the Torque Converter Clutch is not locked up.
Cold advance is easy to test: Look for the 2 wire switch in the T-Stat crossover. On a hot engine, unplug it and make sure it's "open" across the contacts. Cold engine the contacts "short". X2 on making sure the T-Stat isn't stuck open.
Simpler test: Stone cold engine turn ignition on - do not start. Open hood and manually work throttle. The Fast idle should drop and hold the throttle open. Unplug the switch in the T-Stat crossover and the throttle should drop back. Wouldn't be the first or the last time the cold advance failed and the IP (hot) idle was adjusted to cold RPM specs.
Transmission
The Service Engine Soon light will almost never come on. (I have seen it flicker due to wiring shorts around the transmission. Even when the OD planets ate a bearing and sprag clutch with an earth shattering "KABOOM!" and I no longer had OD with lots of codes: no SES light on. ) There are NO EMISSION CONTROLS THE ECM MONITORS OR CONTROLS on 1993 HD Emissions trucks! Therefore it isn't required to turn the SES light on so GM doesn't. What this means is transmission trouble codes can be present without the SES light on. GM did not make a Service Transmission Soon/Now light...
Read codes, if any, out of the ECM with a paperclip as covered in the technical reference section on here. http://www.thetruckstop.us/forum/threads/obd-i-reading-your-codes.3938/#post-47918
The TPS on the IP can be adjusted by back probing the connector to get 0.5v at hot idle. You do this after you have adjusted both the cold idle and hot idle RPM : by the book needed every 6 months. No SES if it's not adjusted properly: just harsh shifting of a limp mode.
You need to count the gears and TCC lockup. I suggest starting in 1 and moving the selector through each gear and being in OD (4th) at 35 MPH. Then take it over 45MPH to feel the TCC lock. This test makes sure everything is working allowing all 4 gears and TCC lockup. I didn't say adjusted properly, I said Working.
IMO you are not obtaining OD and have the 3rd gear manual select over run clutch on. Mis adjusted shift linkage somehow (test above can eliminate) giving you manual 3rd or TPS on the IP not indicating to the ECM you are back at idle? Regardless in manual selected 3rd gear this weak overrun clutch comes on. If the TCC is also locked when you take your foot off the throttle compression braking will overpower this clutch causing a surging feeling esp. going downhill. (If the TPS doesn't indicate "idle" to the ECM the TCC can stay locked.) Eventually (quickly) the clutch pack burns out and you get no compression braking in manual 3rd. All forward gears do not notice this fried clutch pack and work fine. This clutch pack can compression brake if and only if the Torque Converter Clutch is not locked up.
Last edited:
Will L.
Well-Known Member
No, high voltage cant raise rpm regardless of ip anyway that I can think of.
Will L.
Well-Known Member
Even if 93, iirc it is not variable voltage going to high idle circuit on db2. Just on or off. I know the 2 wire temp sensor temp: ohm , but 12v vs 15 volt still cant jump rpm like that.
Something else is going on. Do you have cruise control? If so, start engine and verify high idle then shut off engine. Disconnect cruise control cable from IP. Restart and check.
Something else is going on. Do you have cruise control? If so, start engine and verify high idle then shut off engine. Disconnect cruise control cable from IP. Restart and check.
- Staff
- #7
My point was 93 DOES have a fast idle solenoid, he said 95 which as we know is ds4 and does not. So high idle problems are completely different between 93 and 95, and diagnosed differently between dbc and dbw.
JMJNet
Recruit
Yep, 93 in the Original Poster (craig_marshall) and 95 in Gunnar are 2 different trucks as stated above.
My suggestion is the same, Gunnar needs to create a new thread as supposed to hijacking the original thread.
It is NOT polite to do so even if it is the same truck owned by 2 people. LOL!!!