HEGO headache!
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Elder User
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From: Small acerage in Nebraska
HEGO headache!
Here's my latest problem. Error code 41.(continuous) Ecm is dumping lots of fuel into the cylinders causing it to idle erratic and exhaust reaks of unburned fuel. A new HEGO sensor did not clear it up. Also checked the wiring from the sensor plug to the ECM, everything ohms out great. Nothing shorted or open with good ground. Open for more troubleshooting tips. Any ideas? 
Lead Driver
Joined: Sep 2002
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From: Gateway to the West
Check for vacuum leaks... yes, I know that sounds counter-intuitive but a vacuum leak dumps more air into the system and the computer will compensate by running the mixture very rich. A good working O2 sensor will actually HELP this problem manifest itself.
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Elder User
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From: Small acerage in Nebraska
I have found part of the trouble, an exhaust manifold bolt on the flange was loose causing an air leak upstream of the O2 sensor. 41 went away but still have very erratic idle and when at operating temp, it is stalling at traffic lights. Idle still smells rich, but runs good from 1500 rpm and up.
I removed a vaccuum line from tree( goes to cruise control) and engine gained rpm slightly and smoothed out! :S
Have 40psi and steady fuel pressure. Injectors are stock, cleaned and tested by a local diesel tech 12,000 miles or so ago, t-stat is 180F.
I removed a vaccuum line from tree( goes to cruise control) and engine gained rpm slightly and smoothed out! :S
Have 40psi and steady fuel pressure. Injectors are stock, cleaned and tested by a local diesel tech 12,000 miles or so ago, t-stat is 180F.
Hotshot
Joined: Jul 2002
Posts: 14,285
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From: Bend,OR
ok the Tstat is the incorrect temp. you need to install a 195* tstat. the efi expects the motor to reach this temp otherwise it will run rich which you are experiencing.
also if there is fuel in the oil i would change it before you drive it to much. the gas will wash the bearings and cause damage.
also if there is fuel in the oil i would change it before you drive it to much. the gas will wash the bearings and cause damage.
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Elder User
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From: Small acerage in Nebraska
Not sure which t-stat is in there, might change it anyway,won't hurt anything. Gauge comes up to about n-o in the "normal" Dual core radiator might have some to do with it, needed new one and was planning on some heavy pulling. Computer is not "seeing" the HEGO somehow. Someone I talked to sugested putting older 3 wire o@ sensor in. Personaly don't think the extra wire is causing the problem.
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Lead Driver
Joined: Sep 2002
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From: Gateway to the West
Depends on the O2 sensor that the computer is "expecting" to "see". Some units are EGO some are HEGO. The difference is that the "H" stands for "HEATED". The HEGO sensors have a heating circuit in them to preheat them as soon as the engine is started. Otherwise, the O2 sensor is the ONLY sensor in the truck that actually generates its own electrical signal back to the computer. As long as you are running the same type sensor as the original wiring/connector for it dictates, you should be fine.
Whatever you do, DON'T run the truck with a known vacuum leak. That's worse for a rich condition with the way the system operates.
Whatever you do, DON'T run the truck with a known vacuum leak. That's worse for a rich condition with the way the system operates.
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Elder User
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From: Small acerage in Nebraska
That sounds like a million dolar winner Grey, EEC is from and prom'd for EGO, '91 has HEGO. Should I ground the Orange wire from the EEC as it is shown on the '89 diagram. I thought of it today while talking to a buddy at the tire shop. Strange this should show up 3 months into driving it.
When doing tests on the harness found something odd. KOEO-with EEC connected, pin 26 is grounded, pin 46 has 4.9v to ground. Is this right? I can't remember where I looked for this test. Have been studying too many sources for clues.
Good news is I have a 5.8, all of the engine/ front chasssis harness and EEC from a '90 F250 with ZF tranny. When I get this engine rebuilt it is so going under my 91 hood,ZF and 205 t-case with the twinstick shifters! Will need the tranny, Ever seen a ZF busted clear across the bellhousing? Truck was used for snowplowing, definately abused!
When doing tests on the harness found something odd. KOEO-with EEC connected, pin 26 is grounded, pin 46 has 4.9v to ground. Is this right? I can't remember where I looked for this test. Have been studying too many sources for clues.
Good news is I have a 5.8, all of the engine/ front chasssis harness and EEC from a '90 F250 with ZF tranny. When I get this engine rebuilt it is so going under my 91 hood,ZF and 205 t-case with the twinstick shifters! Will need the tranny, Ever seen a ZF busted clear across the bellhousing? Truck was used for snowplowing, definately abused!
Lead Driver
Joined: Sep 2002
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From: Gateway to the West
Pin 26 should definitely NOT be grounded. Pin 26 is reference voltage to the MAP, EVP and TP sensors and if it is grounded out, they won't get the correct voltage... consequently neither will the PCM/ECM/ECU... whatever you wanna call the main computer.
Pin 46 is the signal return from several sensors and should be left to send whatever voltage it carries, back to the computer. This is the "altered" reference voltage that the computer uses to determine fuel/air, spark timing and control other engine functions.
Pin 49 from the computer should run directly to ground (negative) according to the diagrams for 1989 models with the 5.0 and the 5.8. This completes the heating circuit to the sensor thereby making it preheat as it should.
Pin 46 is the signal return from several sensors and should be left to send whatever voltage it carries, back to the computer. This is the "altered" reference voltage that the computer uses to determine fuel/air, spark timing and control other engine functions.
Pin 49 from the computer should run directly to ground (negative) according to the diagrams for 1989 models with the 5.0 and the 5.8. This completes the heating circuit to the sensor thereby making it preheat as it should.
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Elder User
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From: Small acerage in Nebraska
That helped some. Took the HEGO sensor out and installed the EGO from my '89. Plug end was damaged so I took 4 wire pin off another O2 and wired it in. Took orange wire out near the passenger fender and used a female from an unused wire to make a ground connection. Also disected the main harness, from ECM to under the air box. Cut an orange wire that run to ground, factory spliced to the '91 gray/red for the sig return. Still idles funny,but has improved alot.
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Elder User
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From: Small acerage in Nebraska
Just an update... No error codes so far, but still running rich at idle. Taking it to muffler shop to replumb the exhaust pipes, including an X-pipe for the O2 sensor. Am hoping this helps. I don't think the sensor is getting hot enough to read properly at idle. We'll see if this works 
Lead Driver
Joined: Sep 2002
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From: Gateway to the West
I know you have been dealing with this for a while now but just to be certain... you have checked for vacuum leaks I assume. Vacuum leaks will actually cause the system to run rich (computer compensating for the extra air in the system from the leak). If the problem still persists and you have no vacuum leaks, you may have an ECT sensor with a problem. This doesn't always trigger a fault code because the sensor can be sending a reading that is "within acceptable range" but NOT actually be correct for the actual engine temp. This "stuck cold" condition will cause a rich mixture as well. If bad enough it will cause hard starts on a hot restart as well.
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Elder User
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From: Small acerage in Nebraska
Because of high freQ hearing loss, occupational hazard, I had a friend double check for vac leaks,found nothing. As for the ECT it checked out, It was brand new several weeks ago, before I sorted out the wiring problems. It runs good down the highway @ 40-65mph. had similar probs with '89 exhaust and it cleared up with the X pipe. Wanted an excuse to rework some of the cobbled mess previous owner had done.