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1991 F250 Trouble codes and stalling


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jhartjen
New User

Jul 24, 2014, 5:10 PM

Post #1 of 4 (1562 views)
1991 F250 Trouble codes and stalling Sign In

I have a 1991 F250. The CEL is on and is displaying code 63 (TPS voltage too low) and 98 (hard fault). I have replaced the TPS and IAC valve. Codes are still present. Truck also stalls after about 30 sec to one minute when put in gear (reverse or drive). Runs fine in in park and neutral except the idle is a little high (about 1200 rpm).


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Jul 24, 2014, 9:41 PM

Post #2 of 4 (1540 views)
Re: 1991 F250 Trouble codes and stalling Sign In

OBDI codes don't tell you as much and neither tell you what to do just what it notices for an area to look. Don't have the paper book for it in front of me but don't know what you mean by "hard fault" for code 98. In fact what engine is in this first and foremost?


1991 - old enough and no problem but rather than tossing parts already look for common problems for age like vacuum leaks. Runs fine (you said) except high idle and stalling when in gear after very short time from cold start?


Slow down and let's find out what engine is in this and start over. Tossing parts you are actually going to make it harder as each item doesn't change anything you then question all those and it's probably just one issue if not provoked by something like recent work or an overheat for example,


T



jhartjen
New User

Jul 25, 2014, 8:38 AM

Post #3 of 4 (1526 views)
Re: 1991 F250 Trouble codes and stalling Sign In

It is a 5.8l, 351. Some of the vacuum lines look ragged but not busted up. I have tried spraying carb cleaner around the connections and heard no changes in rpm's. Did that in the dimming light of evening and will do a visual inspection in the next couple of days.


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Jul 25, 2014, 9:13 AM

Post #4 of 4 (1520 views)
Re: 1991 F250 Trouble codes and stalling Sign In

OK - You made me go get the paper book. Correct on the codes. #98 is just telling you it knows and is a hard code not which. Other was low voltage TPS doesn't not mean it's bad. Plug to it could be or wire to it OR you can install those wrong not catching the little tabs. Been a while there should be two colors of the inside turn part blue or black I think. Use the same as when it worked properly and IDK why they are different as both seem to work the same in my own testing.


It's telling you the problem exists when engine is running or just key on engine off. Take all this with a grain of salt for reader and the results but do some basics before going nuts. Unplug it and see the idle change lots. That suggests to me wires are intact to it.


I'm not convinced that other issues could set you to a TPS code. If you can get a stable idle check plain actual manifold vacuum with a "T" in line. Unless super high altitude should read about 18Hg or so and if not let me know well test more.


The carb cleaner vac leak testing is good usually but don't forget PCV hose and impossible to reach grommet for it down back.


Hoses look lousy as you said. Hose is cheap just toss them one by one and I think even trucks crossed over to fender well with a plug of vacuum hoses that were/are still a nylon like wire not rubber. Can patch with hose that fits. Checking trans fluid pulls on those lines too so take a look as ages ago they were brittle as raw pasta.


Reason is vacuum is the measure of both condition of engine, valve timing and what load it's under. Idle is none really so high Hgs. Full throttle there's about none and everything in between. With that it decides timing, fuel delivery with other inputs too but if a vac leak is there it thinks it needs more fuel perhaps if reading is low and screw up other adjustments it's making.


Distributor worn shaft bushings, original timing cam gear if known and vac leaks are most common for this engine so far to me.


TPS new or not you can see ohms sweep testing old and new that they are smooth is what to look for while turning throttle plate.


Sorry, been a while. EGR diaphragm could leak and gasket to it or pintle doesn't seal well. Need to look at it mostly which of course wrecks the gasket.


One more for now. Check integrity of all intake air items including routing from fresh thru filter and tight to throttle body. See what you can see wrong if at all and go from there for now at this age. Strong engines but nothing likes things wrong or broken,


T







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