Hello everybody

My truck is a 1986 F-150 4x4 302 EFI. I have pulled codes from my computer using the 'Key On Engine Running' test as per Haynes Repair Manual. The two codes are as follows:

Code 31 - PFE, EVP or EVR circuit below minimum voltage
Code 41 - Oxygen Sensor circuit indicates system lean

Concerning 'Code 31', I don't know how to proceed in correcting this code. As far as I know, the code deals with the EGR somehow. The electrical connection on top of the EGR appears to be good. The vacuum line running to the top of the EGR is connected; however, when I pull that end off and blow into it, I can hear air leak somewhere near my right fender wall by the charcoal canister and a line of relays. I can't pin down the location of the leak. Is this normal?

Concerning 'Code 41', I installed a new oxygen sensor last week. I don't know why this code is appearing.

Any information on how to correct these codes will be appreciated.

Thank you all for your help

Joel

 

By the way, I forgot to mention that my truck pings alot under heavy accelaration or load. My time is set to 10 degrees BTC as per sticker on front of truck. I have reviewed list of causes of engine ping in the Haynes repair manual and the only thing that seems to makes sense is lean fuel mixture. I have a new oil pump, new distributor, and new plugs. Is there any relation between my enging ping and the codes mentioned above?


Thank you for your help,

Joel

 

An inoperative EGR system can also lead to pinging at part throttle. If it pings at full throttle, I would make sure the fuel pressure is correct and that there is enough fuel flow.

 

I'll tell you what you can do... Take your EGR valve loose from plenum and flip the gasket so that the hole is blocked. Then re-attach it and remove the vacuum hose from the unit (Leave the electrical connector on there). That temporarily disables your EGR system and hopefully your pinging will stop. You can't legally leave your EGR disabled because it won't pass emissions like that, but at least you can diagnose the problem and go from there.

I suspect your EGR valve is not seating properly and causing a lean condition (the code 41). You can inspect the valve itself if you remove the sensor from the top of the unit. Since you are getting a code 31, that is probably the case.

 

Proper flow through the EGR valve enrichens mixture and cools combustion chamber temperatures. So, lack of flow leans mixture and increases temperatures ... either of which can cause pre-ignition. Blocking the EGR flow will insure pre-ignition.

It sounds like the EGR is not opening or not opening enough, leaning the mixture. That could cause the code 41. Problem probably lies with the EGR valve, postion sensor, or the vacuum regulator.

You can check the EGR valve by holding accelerator open a little (keep it steady) and pulling and re-installing the vacuum line to the EGR. Engine speed should change and you should actually be able to see the stem move on the EGR valve.

I had a similiar problem that turned out to be the vacuum controller. Idle was a little rough, but you could pull the vacuum line off the EGR and it would pick up and smooth out (valve wasn't closing all the way). I also had a code 41 - lean mixture, so the valve wasn't opening enough either. Valve was new, had already been replaced.

 

I'm sorry, I was wrong, EGR flow does richen the mixture. Thanks for the correction. I wanna point out though that blocking the EGR flow will not cause pre-ignition as long as the computer knows the valve is closed (thats why i said disconnect the vacuum line). My truck has been running fine with the EGR disabled for over 8000 miles now. That only works if the valve is working correctly though. I would follow pctours advice and check it a different way. Thanks again for the correction.

 

Thank you for your advice.

Today, I pulled the upper intake manifold off. The gasket had a small tear. I replaced the gasket. There was some oily residue inside the upper intake manifold and appears that some oil was getting blown into the upper manifold through the pcv valve. I assumed my pcv valve was a bad and replaced it with a new one. Cleaned off the upper intake mainfold, then put it back on the engine.

I installed a new EGR valve and sensor. I disconnected the Negative battery cable to clear codes and reset the computer. Afterwards, I took the truck for a short drive then returned home. I checked the engine codes and I am still getting Code 31 & 41. ???????

I still have strong pinging when under load or heavy accerlaration with timing set at 10 degrees BTDC. I am assuming that the problem with engine ping and the problem with the two codes are related. However I have not found out enough information to either prove or disprove my assumption.

Right now the only remedy for the ping is to set my time aroung 20-25 degrees BTDC according to the timing marks. The ping goes away and I have more power. However, when I check my engine codes, I still get code 31 & 41.

I'm at my ropes end on what to do. Any fresh ideas will be greatly appreciated.

Joel

 

That doesn't make sense. The pinging should be much much worse at 20-25° BTDC than it is at 10°. I would start looking at the wiring to the O2 sensor to see if there are any problems such as shorted or broken wires.

 

I apologize about the misinformation on timing of my truck. I was wrong about what the timing is set on and I am unable to be definitive on my time. The time is currently set to where the timing mark is at the 12 o'clock position on the harmonic balancer to take the ping out of the engine.

About two months ago, I replaced the harmonic balancer on the truck because the old one had slipped internally and the timing mark was off about 30 degrees. I am suspicious that the new one may have slipped as well. What could cause the harmonic balancer to slip?

It has been suggested to me that engine may have been overhauled and the pistons, rods, etc. may have been reinstalled out of order. Could this have caused the harmonic balancer to slip?

Again thank you for you advice.

Joel