Hello all, I'm getting a code 41 on my 1989 Ford F250 with a 460 & C6 tranny. I see that code 41 is showing that the O2 sensor is reading lean and this is causing the computer to dump more fuel into the engine as the engine is actually running a bit rich. I will be getting a fuel pressure gauge tomorrow to get an actual reading but I have pulled the vac line from the regulator and there wasn't any fuel in the vac line. Plugs are a bit dark but show no signs of oil and the truck doesn't use any oil. Exhaust also smells rich.

There was a huge leak around the O2 sensor because the threads were completely stripped and the sensor was just wired tied in!! I figured that this was the culprit because of the exhaust leak.(There are no other leaks ahead of the sensor) So, I welded a new bung on and now have a good sealed O2 sensor. Also replaced the sensor while I was at it with a Bosch. I have checked the truck for vacuum leaks but haven't found any. Checked brake booster, cruise has been blocked off for some reason and I don't want to reconnect for the fear of a catastrophic failure lol. Found a cracked HVAC line and repaired it but there was no difference. (Still need to test each individual circuit... I know the carb cleaner isn't the best way to find a vac leak especially on these trucks with so many vac circuits) Replaced plenum and TB gaskets after disassembling and cleaning it. Checked for leaks on intake and plenum even after replacing gaskets.

The only "mod" other than a custom catless exhaust is blocking on the EGR (I know this is a disputed mod). I made a block off plate and got a gasket. The original block off plate I made was warped and leaking. Made a new plate and it no longer leaks. I left the EGR plugged in and vac line attached to keep from throwing a code. Haven't looked into the TAB/TAD solenoids and honestly don't know too much about them. Since the exhaust is custom and with no cat, I have obviously disconnected the A.I.R system. Hoping to get a shorter belt soon to completely bypass the pump and clean up the engine bay a little bit. If the EGR being deleted has something to do with this, I will by all means by a new tube (old one cracked while trying to loosen the nut on the bottom of the EGR) and re-install the EGR.

TPS is at .9v when closed, IAC is new after the old one started sticking (Motorcraft part). When reconnecting the O2, I was checking the wires and discovered that the purple w/ the orange tracer wasn't supplying 12v like it was supposed to. Traced it up thru the firewall and found it completely burned after entering the cab all the way to the fuse block. I replaced the fried wire all the way from the fuse block. In doing this, I also figured out why my reverse lights weren't coming on as they also feed off the wire that supplies 12v to the heated 02 sensor. Another concern I have is that I am getting 3.6-3.7v on the dark green/purple wire which is the signal wire to the PCM (On chassis side of harness with O2 disconnected). Do you guys supposed something is shorted in the PCM? A bad ground to the PCM? There are some ground straps that are broke or missing and I do know that the engine has been out of the truck or at least taken apart because someone has taken a scratch awl and labeled all the plastic connectors. Maybe they forgot a ground some where???

Truck runs great overall and has plenty of power. Also forgot to mention, the truck has had a tune up including plugs, wires, cap, rotor, new Motorcraft distributor pickup, air & fuel filters. Also got codes for ECT and IAT but I figured that they were just because the truck wasn't warmed up before preforming the KOER test ( I believe the truck needs to be at operating temp... please correct me if I am wrong). Found a plug wire that had gotten on the exhaust manifold so I taped it up and routed it out of the way of any obstacles. I know I need to do a bit more diagnostics but if anyone has any ideas, especially about that mysterious 3.6v on the signal wire coming the the PCM (pin 29 I believe but not 100% sure on that) I would really appreciate your help. Trying to get this truck into tip top shape as it is becoming my daily driver. Thanks in advance!!

 

Update: Did testing with a hand held vacuum pump and discovered that the TAB, TAD, and EVR circuit isn't holding a vacuum. Is this circuit supposed to be holding a vacuum? Or does it start holding vacuum once the solenoids are actuated? One of the valves is making a buzzing sound as the vacuum drops. You can here this when you shut off the truck and also when you use the hand pump. HVAC holds good vac but does drop to about 5 in hg after setting for 2-5 min (pumped up to 20 inhg). I doubt this would be enough to cause a problem. Vacuum is 19in hg at idle and doesn't fluctuate. Still need to get a test on the fuel pressure.

Did a compression test....
1: 150
2:151
3:140
4: 147
5: 130
6:146
7:151
8:150
That 140 is borderline and that 130 is definitely concerning. Maybe a cause of the miss? Not sure...

Update 2:
Put oil in #5 and it went up to 151 so at least the rules out the top end( burned valve or bent pushrod) and points me towards the rings. Need to do a leakdown test...
Re tested #3 and got 145 on a 2nd, 3rd, and 4th test. Better than 140... Should try another one of my gauges on it to rule out all possibility of a faulty gauge (not using any el cheapo gauges either....)
Still wondering about that 3.6 v on the signal wire from the PCM too...

 

Code 41;
You want to make sure you have a good ground closest to your O2 sensor and the Engine/Body grounds.
I suggest you measure the resistance from the base of your O2 to the body and engine grounds.

(On chassis side of harness with O2 disconnected) Was this the output of the O2, or was this back to the PCM?
(3.6vdc?) Check your meter scale, O2 puts out 0.0 to 1.0 vdc.

Ultimately you need to check voltage at Pin 29. It doesn’t take much resistance to knock the signal down on a 1-volt circuit. There may be connectors along the way, you will want to check, clean and measure the voltage/resistance along the way.

Also check the resistance from Pin 29 to the O2 connector.

 

 

That Capacitor looks fine to me.

Not surprised that the EECM was replace along the way, you have a 30 year old truck.

The part numbers I see in the photo are 1989 Ford numbers.

Was that mounted behind the Left-Hand Kick panel?

 

Check EECM Connector Ground Pins # 20, 40, 49 & 50, you should have 0 resistance to ground.

 

That is a concern, since that system connects directly to the exhaust at the engine it must be sealed air tight or you have a giant air leak upstream of the O2, best advice is remove it all(hoses,valves,pump) and plug everywhere it connected to the engine/exhaust. TAB and TAD solenoids should remain electrically connected and vacuum lines should be capped.

What are you using to measure that? If it's a multimeter that is no good you need an oscilloscope, with that you can see if the O2 is switching as it should. You can't measure a sensor input like this with a multimeter, it's a high impedance and depending what you are referencing it to you will see different voltages. Given that you found and fixed a burnt wire to the O2 heater which is very important to it operation you might want to consider this good for now, deal with the air system, clear codes and then see if anything changes.

If the computer is running open loop all the time because the O2 is disabled then the motor will run great but that is because it's rich.

You are correct.

 

Looking at the blue capacitor, on the left of it(1st photo) there appears to be discoloration under and to the left.

It also appears that way in the 2nd photo but I can't be certain if that's shadow or not.

 

Ok just an update... haven't done any further testing as I am waiting on my OTC breakout box to get in. Once I get that I'll be able to do more diagnostics and let you guys know whats going on. Don't really understand how the air system is causing a leak because the only pipes I disconnected were the ones coming from the pump which went into the cat which is gone now.

 

Hello, sorry for the delay but I have finally gotten some more time and have been working on my truck again. So I got my breakout box in and tested the voltage at pin 29 and got .7 vdc. Not really sure where this lies one the scale of lean to rich... though I found them on here somewhere a while back but I can't find them now.

Also, originally I said plugs were dark but now they are actually looking a bit lean to me... maybe someone else has a different opinion...

I'm also getting surging/loping at idle almost like the truck has a cam in it... which it may but, I doubt it. I checked the purge solenoid and to my surprise it was disconnected from the vacuum source. The solenoid itself is shot so I guess that's why someone disconnected it. I'm at a loss because I'm not just stabbing in the dark. I'm trying to use all the proper tools and follow all the proper steps but I'm getting nowhere.

Another issue that has just came up is sometimes the truck starts up with a blip of the key and other times it takes 5-7 seconds of cranking to start and it really sputters when it does start. I still need to check fuel pressure on it. I rechecked the timing on the truck and surprisingly, it was almost at 0 with the SPOUT pulled. I re set it to 10 BTDC but it didn't seem to make all that much of a difference. Why would it have slipped back like that? I tightened the clamp good and there isn't much slop in between turning the crank and the reaction of the rotor. The numbers are also steady and don't jump around when I have my light on it.

Your help would be really appreciated, Thanks in advance!

 

 

 

What are the readings from cold start to warmed up ?

 

EDIT; answered my own question....

 

Problem has been solved! I discovered that the orange ground wire on the LH rear corner of the intake had broken off from its connector on the intake. Reconnected it and drove it around. Pulled codes again today and didn't get any lean codes. Only code I got was the ECT sensor and this time the truck was hot. I guess I may as well replace it since the truck was warm and I was still getting the code.