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I posted this in the van forum, but since the Bronco forum gets more traffic, perhaps someone here can help.
1991 E350 with 5.8L and E4OD, 195K miles. Recently rebuilt transmission. About 600 miles after rebuild of transmission I started to get periodic erratic shifting (into neutral at hwy speed, 3rd gear at slow speed, etc). Pulling error codes after a short drive always reports 452, VSS error. BTW, I also have EGR errors (327, 328), and have a new EGR valve waiting to be installed.
I've replaced the VSS, the plug to the VSS, and tested the wiring from the VSS to the ECU as per the factory engine diagnostic manual--all tests good. I can hook a voltmeter to the VSS contact at the speed control unit (under the dash--wiring diagram shows a direct contact to the actual VSS), and I get a very steady voltage rising with speed.
I don't think the VSS error is a problem with the VSS or wiring at all. This 1991 model predates the PSOM, which apparently causes this kind of problem in later Ford vehicles (1992+). My VSS is wired directly to the ECU, and the Speed Control (currently disconnected)--no other connections to this circuit. At this point I'm stumped.
Does anybody know how the ECU confirms accurate VSS data (and thus would report a VSS error even if the VSS is working)? What other sensors should I be considering here?!
To McLeod's point, do you have access to an oscilloscope that you could use to more easily identify a missing tooth on the tone ring or abnormal gap (indicating a cracked tone ring)?
Also, are you positive that you don't have a PSOM, or just going by what you've read online? What's the build date of your E350? If it's late in the 1991 model year, maybe it received some updates. I don't have access to the wiring diagram for 1991 (my stash starts in 1992) to see if there's any "Early/Late" designation for the speedometer/VSS circuit.
I replaced the speed sensor (and plug) in the transmission (with motorcraft). The rear differential on my 1991 E350 has an antilock brake sensor, but it appears to be completely independent of the VSS for the transmission/ECU. Also, the anti-lock system is working correctly and reporting no errors.
Yes, I'm positive there is no PSOM--I have an old-style mechanical speedometer cable that runs from the transmission (sticks into the VSS) directly to the speedometer.
I haven't had a chance to work on it this weekend, but will get back at it later this week.
If you do not get enough help here try 87-96 larger f series trucks, transmission related issues mark k. Is an ex x mission tech and knows tons. Also sounds like your on the right track with your issue,I am not knocking the advice here ,just supplementing .TR
About 600 miles after rebuild of transmission I started to get periodic erratic shifting (into neutral at hwy speed, 3rd gear at slow speed, etc). Pulling error codes after a short drive always reports 452, VSS error.
Shifting to neutral at highway speeds is almost always a failing TRS (also called MLPS.) That's the sensor on the driver's side of the trans. This type of failure will not set a code. Replace the TRS.
Originally Posted by sail2fast
I've replaced the VSS, the plug to the VSS, and tested the wiring from the VSS to the ECU as per the factory engine diagnostic manual--all tests good. I can hook a voltmeter to the VSS contact at the speed control unit (under the dash--wiring diagram shows a direct contact to the actual VSS), and I get a very steady voltage rising with speed.
I seem to remember that the VSS on this vintage was on the transmission tailshaft. Is that the VSS you're looking at? Of course, it's been over 30 years, so I could be wrong.
Originally Posted by sail2fast
I don't think the VSS error is a problem with the VSS or wiring at all.
If you're getting a code 452 the problem is with the VSS, wiring, or the tone ring.
Originally Posted by Black Ford XLT
If you do not get enough help here try 87-96 larger f series trucks, transmission related issues mark k. Is an ex x mission tech and knows tons.
VSS hell continues. I did successfully replace the EGR valve yesterday, so now the only code I get after driving is 452. I have inspected all the connectors and wiring involved in the VSS circuit, and tested the wiring run with a multi-meter. Everything looks very good and tests as it should. If I clear all the codes and go for a short drive, I always get code 452 back again.
I did several 5 minute drives including highway speeds--the transmission shifted perfectly and when expected. But still code 452. I don't have confidence that erratic shifting won't return.
The only part of the wiring I haven't inspected is the grounding location for the VSS signal return (G100)--not sure where it is. However the wire tests correctly at the ECU plug.
SO: Is there any chance this is a bad ECU? Other comments I've seen indicate a failing ECU would cause more problems, but if there were a bad solder joint related to the VSS circuit in the ECU then perhaps that's my issue. What do y'all think?
Yes, clearly the PCM needs repair. I feel like I've done enough research that this must be the problem (fingers crossed). Enough so that I put everything back together while I wait for a PCM to arrive. I think it will live again! Thanks, everyone, for your support.
