I have been on other forums can’t find any info to help me. I’m hoping someone has had a similar problem and can help. Okay so I bought a 92 f250 7.3. It has never shifted good from the day I picked it up so I ran threw the check list. TPS, tach, shift selonoid harness inspection and ohms test and selonoid pack test. I found the tps was way out of spec and old so I replaced that and tach sensor. TPS is set to 1.14 at ct and 4.3 at wot. Now is where the problem begins. At that setting the truck shifts at like 3500rpm from 1-2gear even higher into 3rd and I can’t makr it into od for fear of smoking the trans completely. Also every shift feels like a car crash. I’m seriously afraid the driveshaft is going to snap it shift so violently. If I set tps to .74v it shift around 2000rpm 1-2 and a bit higher into 3rd and od. But lugs just feels like crap and I won’t even try to pull a small trailer with it like this and is Still quite hard but not violent. Only code I have is 11. I believe that means all is good. Can anyone please help me to get this truck shifting properly. I have a rebuild kit for it but would like to save that for very last option and I would hate to rebuild and find I still have the same problem. Thanks
E40D help please!
- Thread starter Texas27
- Start date
Welcome to oilburners, hopefully we can help you figure out these issues. Does the tps seem to range the voltage smoothly? No jumps or bumps when you go through the throttle range? I would try to set it a 1v at idle with the engine hot and see how it acts. Seems 1.14 is too aggressive and .74 is too low, gotta find the happy median.
TPS Voltage is smooth from close to open no drops, spikes, or stalls. I have had it set to .95v yesterday and it was still shifting super late and hard and I had to drive it home so I just kept adjusting down in voltage until it was at least driveable to get her home that’s when I found that.74v was soft enough to make it home. I put a new tcm in and found my tach wouldn’t work and it was not working at all so I went back to the original tcm from the truck and tach came rite back on so I think I just waisted 140$ on a computer. Do you suppose even tho I have no codes that the computer may be messing up the trans? Like I said shift packs checked out so did all wiring but I do not know if There is any test for the computer I’d imagine I would have to try testing it while driving to figure out if it is operating correctly. But I do not know.
What tcm did you buy? I believe the new replacement computers need the harness to be repinned to work properly so that may be why you lost tach, it’s either the mlps or the computer that needs repinning upon replacement, can’t remember off the top of my head.
Does the trans shift fine if you shift it manually? Are all brake lights working including the third brake light? You shouldn’t have to adjust it that low for it to be driveable.
Does the trans shift fine if you shift it manually? Are all brake lights working including the third brake light? You shouldn’t have to adjust it that low for it to be driveable.
What does the fluid look like? Do you know if the trans has been modified or has a shift kit? Just trying to nail everything down to narrow down the possibilities.
I may be jumping threw voltage to much when I adjust. I guess I should ask, just how touchy is the tps? Will .1 or .2v make a huge difference? When I was adjusting I went from 1.14v down to .95 then .90 then .80 until I was going for .75 but got .74 and just drove it home. Should I be adjusting it in much smaller increments such as .2v up or down?
Sorry didn’t see the reply’s until I posted again. The fluid is brand new replaced last week. Lvl is correct mlps is now and the computer may be the one that needs to be pinned considering mlps when in fine. I have changed a number of them strait out of package to trans no problems. What I know about trans. It is a jegs reman do not know when, old fluid was dirty but not burnt little slug on magnet nothing concerning. 3rd break light is out but all others are functioning correctly. I did not notice that bulb was out until just now. And the computer I bought was from Napa I do not know part number there was some confusion and I think they ordered on for a 5.8.
That small of change won’t make a huge difference, change that third brake light then go from there
Sounds good. I won’t be able to change it until tonight or tomorrow I have britday party’s today that I have to make appearances at. I will post back when I get that replaced and see how it goes from there. Thank you for your advice.
david85
Full Access Member
It sounds like the TPS is still having some of the desired effect in terms of shift scheduling, but line pressure (and resulting shift firmness) seems to always be at maximum. Does this sound about right?
If yes, I wonder if the EPC (Electronic Pressure Control) solenoid is stuck to max setting...something that could happen if it gets no power...but a code scan *should* catch that. If the EPC were physically jammed however, the coil could still have the correct electrical properties even though the solenoid was no longer moving to properly modulate pressure.
All of this might result in the TCM thinking everything is fine, even though the EPC is no longer modulating based on the variable TCM output signal. From what I understand, the TCM fault codes are intended to catch slow shifts in order to prevent slipping (and resulting burnup of clutch packs), so excessively firm shifts won't generate a code.
If yes, I wonder if the EPC (Electronic Pressure Control) solenoid is stuck to max setting...something that could happen if it gets no power...but a code scan *should* catch that. If the EPC were physically jammed however, the coil could still have the correct electrical properties even though the solenoid was no longer moving to properly modulate pressure.
All of this might result in the TCM thinking everything is fine, even though the EPC is no longer modulating based on the variable TCM output signal. From what I understand, the TCM fault codes are intended to catch slow shifts in order to prevent slipping (and resulting burnup of clutch packs), so excessively firm shifts won't generate a code.
I have been thinking about the line pressures. Like I previously said that my tps has been set properly and I have been threw the check lists time and time again. I do not have a gauge to test pressure but I do have a new shift selonoid pack I can put in. One question tho. I have 4 selonoid packs on my shelf I know 2 are for a 5.8l and 2 I’d for the 7.3l. Unfortunately I did not make what is what and they look identical. Is there any difference between one for 5.8 and the 7.3 selonoid pack. The connector, pin, plug is the same.
david85
Full Access Member
After dusting off my manuals, I don't see any evidence that there is a gasser or diesel solenoid body. There are differences based on model year, but not engine type.
The major difference is 1995 and newer, where a line of diodes on the integral circuit board of the solenoid body was relocated to the TCM. The connector pin arrangement was also revised to eliminate redundant pins. So if you plan to run a 1995-up transmission on an older vehicle, you need to swap the older style solenoid body in there to work with the older style TCM.
The solenoids themselves are on/off devices, so there is no 'calibration' related to them; they either work or they don't. The EPC is an analog device, but line pressure curve is controlled by the TCM, so I see no reason to make a different version for the diesel vs gas.
The on/off solenoids can be checked with a multimeter set to ohms. Each solenoid should show 20-30 ohms.
The EPC should be 4-6.5ohms. The EPC procedure also calls for teardown and visual inspection in case the internal components are damaged. If I'm reading this right, the EPC uses a spring loaded spool valve and electro-magnet arrangement.
If this transmission was overhauled and the old solenoid body was reused, its entirely possible a piece of shrapnel has jammed the spool valve at the relaxed end of the travel. The relaxed end is with the electrical signal at minimum and the spring fully extended; calling for maximum line pressure. This is done on purpose so that any electrical failure results in max line pressure instead of minimum line pressure (fail safe).
Another possibility is a partial short inside the EPC coil itself. A partial short to ground could allow electrical current to shunt around the coil, thus reducing its ability to push against the spring; which again results in higher line pressure.
The major difference is 1995 and newer, where a line of diodes on the integral circuit board of the solenoid body was relocated to the TCM. The connector pin arrangement was also revised to eliminate redundant pins. So if you plan to run a 1995-up transmission on an older vehicle, you need to swap the older style solenoid body in there to work with the older style TCM.
The solenoids themselves are on/off devices, so there is no 'calibration' related to them; they either work or they don't. The EPC is an analog device, but line pressure curve is controlled by the TCM, so I see no reason to make a different version for the diesel vs gas.
The on/off solenoids can be checked with a multimeter set to ohms. Each solenoid should show 20-30 ohms.
The EPC should be 4-6.5ohms. The EPC procedure also calls for teardown and visual inspection in case the internal components are damaged. If I'm reading this right, the EPC uses a spring loaded spool valve and electro-magnet arrangement.
If this transmission was overhauled and the old solenoid body was reused, its entirely possible a piece of shrapnel has jammed the spool valve at the relaxed end of the travel. The relaxed end is with the electrical signal at minimum and the spring fully extended; calling for maximum line pressure. This is done on purpose so that any electrical failure results in max line pressure instead of minimum line pressure (fail safe).
Another possibility is a partial short inside the EPC coil itself. A partial short to ground could allow electrical current to shunt around the coil, thus reducing its ability to push against the spring; which again results in higher line pressure.
That’s awesome info David85 thank you very much. I’m going to do a test on the solenoids again just to triple check my work and if I find any problems I will switch the pack out. And I will pay very close attention to the epc.
icanfixall
Official GMM hand model
Welcome to the forum. My guess is this has to be electrical feed back somehow. Or you are testing the TPS on the wrong wire. You MUST test from the center wire that goes into the TPS. You MUST have the engine warmed up so the fast idle is off and the cold advance is off. .96 to 1.2 volts at the idle with key on but engine off. Thats koeo.
trackspeeder
Stone crusher.
Gas and diesel use the same packs. The difference is in the years.
I would do a pressure test before playing with the solenoid pack.
I would do a pressure test before playing with the solenoid pack.
