93 F-250. 7.5L engine.

I’m still chasing my weird “runaway” idle. Periodically the temp gauge starts climbing at a rate that engine temp cannot rise at. When this happens the idle will raise.

I need to pull the kick panels and check the ground there. I know that one controls the gauges, that might start to solve the temp gauge, but I can’t imagine that would have anything to do with the idle??

The only code I’m reading is 34, which is entirely related to the EGR and Evan systems. Last night I replaced the entirety of the EGR system. I’ve got a new pipe, new EGR valve, new position sensor and solenoid. There’s a possibility that the problem is in the wiring, but diagnosing gremlins is by far my weakest suit.

I am accepting any and all suggestions at this point.


Thanks


Jeremy

 

Code 34: EVP voltage above closed limit.

When is this code displayed? KOEO, Stored Codes or KOER?

How are you pulling the codes? Count flashes or Code reader?

Was that code there before you replaced the EGR valve and EVP sensor?

 

I bought the Innova Ford OBDI code reader to help me diagnose this problem. I’m getting the codes KOEO engine off. I’m doing my best to “play by the rules” (a rarity for me, typically) but the instruction manual is clear that you don’t go any further with the diagnostic reader until you aren’t getting any stored codes.

When I first pulled the codes I was getting 34 and 61, engine coolant temp sensor fault or grounded. Honestly I’m not entirely sure why I’m no longer getting the code 61. I did replace the gauge temp sender and cleaned and dielectric greased the injection temp sensor.

The weird thing is, my 93 has two temp senders. One theoretically only controls the gauge, the other is for the engine management. The runaway idle definitely happens in concert with the temp gauge reading high, but it’s my understanding that the gauge sender has no relation to the engine management temp sender, so THAT makes no more sense than the rest of it.



Still open to any and all suggestions. I’m getting close to just calling Holley up and ordering their MPFI Terminator setup.



Jeremy

 

All of these trucks have two temperature sensors. One is for the computer to provide Engine Coolant Temperature (ECT) feedback. The other is the same type sender for the temperature gauge that has been used for years and years. So your issue with the gauge reading high and the idle RPM kicking up may not be a coincidence. The computer is designed to kick up the idle RPM when the ECT sensor indicates the coolant temperature ~225F or higher. You may have a sticking thermostat. Verify the real coolant temperature with a mechanical gauge or at the very least use a cheap infrared temperature gun pointed at the thermostat housing to see what is going on.

Let's go back to Code 34. If it is being displayed KOEO only then you need to verify the output is too high with a DVM. Since you did some wholesale parts swapping on the EGR system you have introduced new variables. As we found over the last few years replacement EVP sensors, especially aftermarket, tend to have an actuator shaft that is too long. This increases the closed EGR position feedback signal beyond the allowable range. One way to fix this is use a thicker o-ring between the EGR and EVP sensor. Of file a little off the EVP actuator shaft to bring the signal within range.

The electronic engine control systems on these trucks are not that hard to work on. Going to the Holley system is not really a magic silver bullet IMHO.

 

I’ve been chasing this issue for a while now. The engine is absolutely NOT as hot as it’s presenting. I don’t have the infrared thermometer on me right now, but there was a while there where I kept it in the truck. Upper radiator hose never got above 180-185, thermostat housing read around 200, radiator core was in line with the upper hose. It’s not actually hot, but something is telling the ECU it is…

Another wrinkle got added today. The brake and ABS lights came on. As well as the whole elevated temp *reading* elevated idle. The truck sat for a while before I bought it, but it ran great and has gotten progressively worse. I had issues with deteriorated brake lines, which lead to replacing pretty much the entire brake system minus the hard lines.

Quick question: as this is more and more seeming like a “ghost in the machine” issue, which is why I’ve gone through all the body/chassis grounds, is there any chance the issue is stemming from either a bad alternator or voltage regulator? Being that code 34 is over voltage limits and I’m having other electrical issues, I’m just wondering. I didn’t think it pertinent before today, but the farmer I bought the truck from is a typical farmer, mason jars full of money buried all over the property, but won’t spend a nickel he doesn’t have to. He put a new battery and had the alternator rewound prior to selling me the truck. I checked the charging voltage a while back and it was a little hot… better than 14.4 volts. Today I noticed that the voltmeter is reading almost to the “L” on normal.

I’m really tired of throwing parts at the truck, I’d rather do my best to diagnose the actual problems. BUT! if there’s a chance an alternator that wasn’t rewound by my farmer friend’s friend, it’s worth it.

Just a thought.

Otherwise, what is the protocol so check the EGR/DVM? No matter what I need to get the code 34 cleared.

Thank you for all of your help!




Jeremy

P.S. the EGR pieces were all motorcraft parts. I know that isn’t a silver bullet, but I didn’t just use the cheapest available.

 

Could be a faulty Engine Coolant Temperature (ECT) sensor. Measure it with a meter. Do this when the engine is cold and again when it is acting up.

Engine Coolant Temperature Sensor (ECT)



Check the brake fluid level, there is a sensor in there that will trigger the red Brake lamp if the fluid is low. That will also trigger the yellow ABS lamp. Also check the parking brake and verify it is in the full up position and the switch it contacts is engaged.



I believe 14.4 volts is a pretty good reading. The question becomes is there ripple on the output. That can cause weird issues


At one time part stores used to be able to test alternators not only for voltage/amps but also AC ripple. If they still do that get yours tested.



EGR Valve Position sensor (EVP)

 

I’m cautiously optimistic. Thank you for the advice. Those two links were godsends.

I stacked the old EVP O-ring under the new one on the new EVP and my static values are good enough that I’m not getting either of the codes in the Key Off diagnostic mode.

I have gone through the ringer today with the ECT sender today. Thankfully there’s a NAPA right next door. Using the coolant sensor link you gave me I bought a new sensor and attempted to “bench test” it. Resistance values were right in the outside ambient range. I wanted to get a reading for the high range as well.

So I heated up some water and dunked the new sensor. Well… that was taking too long, so I hit the brass with a MAPP gas torch. While the sensor only got just hotter than uncomfortable to hold, apparently it got hot enough to fry it. When I reinstalled that sensor in the intake the 61 code came right back, check engine light came on solid and the idle went high and stayed the entire time the engine was on.

Without cranking the engine yet, it seems I’m in a better position chasing this thing than I have been. I’m not willing to call it done yet, but at least all the codes have cleared.

The last niggling thing is the brake and ABS warning light. Plenty of brake fluid in the reservoir and as I said, everything but the hard lines are new. I have much better confidence in myself as a hard part mechanic than I do with electrical diagnosis. There’s no issue with the brakes.

The brake warning lights were off on my drive to the shop this morning. They only came in yesterday when the truck got really unhappy with the high idle. And earlier today they came on when the truck was really unhappy as a result of the fried temp sensor.

With both codes off both warning lights are off as well.




I hope to update tonight or tomorrow after I’ve driven a little bit.


Thanks again for the advice, at least I feel like I’m making progress.



Jeremy

 

Sometimes the brake fluid switch float sticks to the bottom of the reservoir or a few cases it is absorbent enough to float mid-range. Take a good look at it.

 

Bumping this thread. To date my EGR 34 code is gone and hasn’t reappeared.

Im still having the same “overheating” issues and I’ll start another new thread for some more advice there.

Thread will be: “How does a bad EEC present?”

Thanks all for the help on this one. The references were a lifesaver.

Also, haven’t seen the brake/abs warning lights since the one time. I’m still leaning towards an electrical gremlin and seeking the advice of the community to root it out. I bypassed the ABS, by removing the spring as was suggested on this forum, so in theory the light should never come on?!?




Be safe



Jeremy