When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Hey everyone, thanks for taking a look! I have a 96 F250 with the 7.5 that's currently not passing smog. All of the monitors won't clear, but everything out of the tailpipe is legal. I've gotten a P0443 (Evaporative Emissions System Purge COntrol Value Circuit) code for 2.5 years now intermittently, and it turns the check engine light on. If I shut the truck off and turn it back on, it's like nothing happened and the light/code goes away. However, the monitors on the OBD2 reset as well.... here is the list of monitors that reset:
Clear after start up immediately (everytime): MIS, FUE, CCM
Will clear after driving some time: EGR
Wont clear ever: O2s, CAT, HTR
Additionally, my speedometer bounces+/- 5 to 10 mph while driving, and this issue started happening around the same time. I've replaced the VSS on rear diff and no luck and on my OBD2 scanner, I register the bouncing speeds so it's not the cluster behaving weirdly. Not sure if connected to this issue, just throwing it out there. Other than that, truck is perfect!
I've done the checklist of things recommended on this forum for this P0443 fix (gas caps, purge valves etc.) and really just think its the computer at this point. Also, a mechanic told me 5 out of the 6 times he saw this, that was the issue. I'm scared to buy a rebuilt one because of the reprogramming and complications with my gear vendors OD kit (I have no idea if that has implications because the previous owner installed it).
With that being said, I'm looking at rebuilding my computer and would appreciate any insight or recommendations on where/who to get that done with.
Additional note: I'm handy(ish) but kind of stop with computer repairs. I know how to solder and could tackle the capacitor issue if that's it... just looking for advice if that's what anyone thinks. Thanks!
For what it's worth I had a CEL on my 91 F250 5.0 after a complete engine overhaul. Bought a $299 OBD-1 code reader. Can't recall what all I replaced trying to clear the codes.
I ended up buying a remanufactured PCM from O'Reilly's making certain all the numbers on the remanufactured matched my original PCM.
When I started it the first time the CEL came on intermittently a few times but has gone away and hasn't come back and no codes.
Damn thing runs great but has no ***** and gets ****ty gas mileage.
Recurring P0443 codes after checking/replacing the vapor management valve (VMV) and wiring has historically been a bad computer. We had one of these recently on the forums which again turned out to be a bad computer.
Your bouncing speedometer could be a bad VSS (you already replaced that one), bad wiring, bad RABS controller, bad bearings in the rear end or a bad PSOM. The Vehicle Speed feedback you are seeing on your scanner is a buffered signal from the PSOM so it could very well be suspect.
You can hookup a simple DVM to the RBS test port, jack up both rear wheels then drop the transmission into Drive. Accelerate to ~30 MPH and watch the DVM, set to AC, to verify the signal is linear as you accelerate and does not waiver as you hold a constant speed. If that is good then take a good hard look at the PSOM.
Recurring P0443 codes after checking/replacing the vapor management valve (VMV) and wiring has historically been a bad computer. We had one of these recently on the forums which again turned out to be a bad computer.
Your bouncing speedometer could be a bad VSS (you already replaced that one), bad wiring, bad RABS controller, bad bearings in the rear end or a bad PSOM. The Vehicle Speed feedback you are seeing on your scanner is a buffered signal from the PSOM so it could very well be suspect.
You can hookup a simple DVM to the RBS test port, jack up both rear wheels then drop the transmission into Drive. Accelerate to ~30 MPH and watch the DVM, set to AC, to verify the signal is linear as you accelerate and does not waiver as you hold a constant speed. If that is good then take a good hard look at the PSOM.
@rla2005 Thank you for the info. Makes sense now that PSOM send to a computer then to the scanner, so that narrows down what can be wrong. I'll give this a go and see what I get. "RBS test port" is this the thing behind the glove box? (referenced here: https://www.ford-trucks.com/forums/7...abs-codes.html)
Hopefully not bad PSOM because I have low miles and that would be a concern if I had to change that out. Additionally, I forgot to add I don't get any weird shifting but haven't tested cruise control recently so I can give an update on that later.
As far as bad computers, do you know anyone/anywhere that could rebuild/repair it? I could do capacitors if that's the problem, but not sure if it needs other stuff.
You mention OBD2 ? My 96 is not that, yours is??
Look inside your PCM, and check for loose and or bad solder areas on both sides of the board. Look for corrosion too, and bad components like resistors etc. Make sure all grounds to body and engine are good and clean. My PCM gets wet, I think it is from the seam sealer issue that is common on these trucks, that is under the cowl vent cover.
You mention OBD2 ? My 96 is not that, yours is??
Look inside your PCM, and check for loose and or bad solder areas on both sides of the board. Look for corrosion too, and bad components like resistors etc. Make sure all grounds to body and engine are good and clean. My PCM gets wet, I think it is from the seam sealer issue that is common on these trucks, that is under the cowl vent cover.
Yes, I have OBD2... I thought that was standard on the 96, but not sure. Definitely gotta crack open the PCM and see what's going on in there. Is there any harm in unplugging it and plugging it back in a bunch (other than putting it in wrong) ? should I disconnect battery and all that?
I'll give this a go and see what I get. "RBS test port" is this the thing behind the glove box?
The test port to check the raw VSS signal is usually located near the driver side hood hinge. On OBD-I trucks the data link to pull codes is also located there.
For reference: courtesy of Subford
Your truck will not have the OBD-I test port.
Originally Posted by mcassett
Hopefully not bad PSOM because I have low miles and that would be a concern if I had to change that out. Additionally, I forgot to add I don't get any weird shifting but haven't tested cruise control recently so I can give an update on that later.
As far as bad computers, do you know anyone/anywhere that could rebuild/repair it? I could do capacitors if that's the problem, but not sure if it needs other stuff.
These later model OBD-II PCMs (computer) trypically do not have the leaking electrolytic capacitor issues like the OBD-I trucks are suffering from. Obviously there is something else going on the trigger these false P0443 codes that I have seen more than a few times now.
Your PSOM can be tested and repaired so you can retain the current odometer reading. Most places can also reset to the Calibration constant counter back to zero. The Full-size Bronco folks have been recommending Module Masters recently to repair PSOMs. Their website also shows that repairs PCMs. Might give them a call.
The test port to check the raw VSS signal is usually located near the driver side hood hinge. On OBD-I trucks the data link to pull codes is also located there.
For reference: courtesy of Subford
Your truck will not have the OBD-I test port.
These later model OBD-II PCMs (computer) trypically do not have the leaking electrolytic capacitor issues like the OBD-I trucks are suffering from. Obviously there is something else going on the trigger these false P0443 codes that I have seen more than a few times now.
Your PSOM can be tested and repaired so you can retain the current odometer reading. Most places can also reset to the Calibration constant counter back to zero. The Full-size Bronco folks have been recommending Module Masters recently to repair PSOMs. Their website also shows that repairs PCMs. Might give them a call.
Thanks for the information, I'll give them a call tomorrow and see what the deal is.
This Hennessey Takes the Expedition Tremor's Off-Roading Capability to the Next Level
Slideshow: The VelociRaptor Expedition gains a lift, upgraded suspension, Brembo brakes, and trail-ready equipment while retaining the stock 440-horsepower EcoBoost V6.
Rezvani's Latest Post-Apocalyptic Monster Is a Ford F-150 Raptor Underneath
Slideshow: Called the Fortress, the 850-horsepower pickup combines Raptor underpinnings with military-inspired features, survival equipment, and a starting price of $285,000.
96 F250 Computer Problems (rebuild?
