Long post so bear with me:

My check engine light came on the other day and my code reader gave me a code 172 and 542 KOEO. The 172 is o2 reads always lean and 542 is fuel pump secondary circuit fault - pcm to ground. I've periodically had the fuel pump code since I got the truck and I'm not too concerned about that right now. However, the lean code has been a reaccuring theme for me.

The truck has had the following work done and runs well: new cap, rotor, plugs, wires, coil, high flow 2nd cat, hollowed out 1st cat and 3" catback flowmaster, o2, and the tranny has been rebuilt. Both fuel pumps and the fuel filter have been replaced, as has the fpr. Fuel pressure is consistant and within spec.

Issues: the egr tube is broken. I've jbwelded it back together but it might still leak, I'm not sure. On a recent trip through the mountains, the truck started ticking. I'm thinking that it is an exhaust leak, maybe cracked manifold or y-pipe, both are old and rusty. I am going to check the timing today if I can figure out which connector is the spout connector. I do know that the distributor is seized to the intake.

Could an exhaust leak or egr tube leak cause a lean o2 code without setting any other related codes? The truck seems to get a consistant 11mpg driven very lightly (I don't have a heavy foot). Even cruising on the highway I get 11 which seems too low for me. I've read about some people having thermactor pipe leaks. Could my I have one of those or would there be a specific code set for that?

Thanks in advance for any thoughts. Todd

 

11 mpg is low. The F250 in my sig gets 13 if driven right. An exhaust leak, EGR tube leak, or thermactor leak could all cause the motor to run lean. I would say there is a good chance, given the code, that the O2 sensor is bad. When my O2 sensor died, it gave me code 173 (rich), replaced the sensor, eliminated the problem.

 

I agree. A leak anywhere in the system before the o2 sensor would probably cause the sensor to give a false reading. Which could cause the truck to run rich to compensate for the false reading the o2 sensor is sending. Which could account for the bad gas mileage.

 

Ok, cleared the codes and took it for a drive, same codes popped back up when the CEL came on. Did a KOER and it was clear. Checked timing after unplugging what I hope was the spout (pink wire and green with black stripe wire). There was a little yellow insert in the plug so I pried that out. Hopefully that was the spout. It was on the drivers fender right behind the test connectors for checking engine codes. Anyway, timing showed advanced 18 degrees so thats a problem for sure. Tried to adjust the distributor but it won't budge. Visegrips aren't working. Trying to find a wrench that fits around there to see if I can force it. my micrometer says 30mm or 1.2 inches.

Would timing that far advanced cause a lean condition? Any tips on getting the distributor to turn (I'm soaking that thing in penetrant as we speak)?

 

Bump to top.

Any thoughts on freeing up the dist.? Did I unplug the spout?

 

Loosen the distributor clamp bolt and turn it with both hands to break it free. My dizzy likes to stick too, but i can usually free it up using both hands.



....... and yes, it sounds like you've located the spout connector.

 

Ok, after soaking it overnight in Deep Creep, I hit the base of it with a chisel and bfh and then reefed on it with a wrench. It finally turned and I was able to reset the timing to 10 degrees btdc. I'm going to take a drive and see how that effects things. I'm also going to check the exhaust to look for a leak.

 

You have a 542 fuel pump secondary circuit fault - pcm to ground failure code, with a 172 system lean code but you are not concern with the 542 fault right now? One is very likely the cause of the other.

That ground is important, if that connection is hit and miss the ingectors may not be firing enough or not at all at times.

That would surly cause a lean condition. If I remember right the fuel pump secondary circuit ground is located on the upper intake, drivers side low and slightly rear of center (front to back).

I think you'll find if you correct code 542, 172 will be corrected as well.

If you need more on info on wire color and or PCM pin numbers just ask.

 

It's very doubtful the timing was set to 18 degrees as these engines will usually crank very hard with anything over 14 and usually not even start.

The spout connector is a two-pin connector with a plastic plug about 3/4 inch wide and 3/8 thick, usually gray but sometimes black. It is located very close to the ignition module, in the same section of wire harness. There is nothing to pry out, certainly nothing yellow. The plug simply pulls out of the connector. If you pried out the small yellow tab inside the connector, that is what locks the terminals in the connector shell. You need to put that back. The wiring diagram for that year shows that both wires at the connector should be pink, but the books are wrong from time to time.

If you pulled out the roundish connector on the cowl, with the light green / black and red / pink wire, that is the test connector for the ABS.

 

Thanks for the responses. FireMe- you're right, I did unplug the wrong connector. I finally found the spout and did unplug it to check base timing. It was at o degrees. I set it to 10 BTC. Afterwards, we took a 200km round trip and I meticulously tracked my mileage: 13.9 litres per 100km or 16.9 mpg! Nice little improvement there and no codes.

Danr1- any further help you can give me with the 542 is greatly appreciated. What exactly am I looking for? A connector? Relay?

 

Nice little improvement there and no codes.

Does that mean no trouble codes appear when driving it after your last adjustments?

No more 172 and 542 codes, or do you only get the 542 now? Both still?

Danr1- any further help you can give me with the 542 is greatly appreciated. What exactly am I looking for? A connector? Relay?

I was thinking along the lines of a grounding wire from the harness that was not put back in place after a repair of some kind. For instance, say if someone took the upper intake off and missed the grounding wire when they put it back on. I'm looking in the Hannes manual to verify the exact location for that ground but so far no luck finding it.

 

Thanks for the replies. Since I properly re-adjusted the timing and cleared the codes, I haven't yet rechecked the codes to see if its in there, but the cel has not come back on. The 542 seems to be a sporatic code. Sometimes it shows up and other times it doesn't. Based on what you were describing it makes me wonder if there is a loose connection. Also, I did a search on "code 542" and did a lot of reading and someone speculated that the code appears for them when they switch tanks while driving. I do that sometimes. I'm going to pay closer attention to what happens after I do that.

Incidentally, after I readjusted the timing and set off on our trip, the first half I didn't see an improvement in fuel economy. It was only after I refilled the tank for the drive home that I saw the improvement. I'm guessing that the computer took awhile to relearn the new settings. Does that make sense?

 

The system lean code doesn't always trigger the CE, when the KOER test is performed is when it shows up if its going to from what I've seen.

And yea I'd check all the grounds under the hood, make sure they are all clean and tight. A sporadic code would suggest that one is loose or corroded, if it was completely off, it wouldn't be sporadic. However some grounds can follow different paths? Unlikely in this case though.

The computer does take some time to relearn things but does so in the first few miles, 10-15 minutes/miles should do it. Should have done so well before the what? 60+ miles the first half of your trip?

I'd recheck for codes even though the light is not on, especially the "key on, engine run" test.

You didn't mention what part of the tests gave up each code, but I would think the 542 code would show up when the KOEO test is done?

 

I was about to suggest the same thing.

 

Danr1 - yes the codes were appearing during KOEO tests. The three times I have done the KOER tests, the truck hasn't generated any codes. As far as the mileage changing goes, I left the house with half a tank so my mileage results on that tank were a mix of old timing / new timing, if you will. Which is more likely to cause lean conditions - retarded or advanced timing?

Eric - if switching the tanks while driving is causing the 542, is that normal? "fuel pump secondary circuit fault - pcm to ground". Does the secondary reference refer to the front tank.