JSRoeth

1993 F1-50 XLT 2WD 4SPD OD transmission - Door Tag Transmission code is letter “T”
VIN #1FTEX15N2PKA69010
ODB1 code scanner is an Innova model 3120
Codes pulled during KOER test:
DTC 42 - Voltage High Runs Rich
DTC77 – Wide Open Throttle not detected

The trouble is: Engine idle varies and idles rough from 500RPM to 1,000RPM, will even surge RPM up and hold steady at 1,200RPM

History of motor: New long block installed by Thunder Bolt Motors, the new motor has less than 1,000 miles
TBM could not solve variable rough idle and told me to run fuel injector cleaner through system.
What I have done since getting the truck back:
I have run fuel injector cleaner through system.
Bought Innova ODB1 scanner
Replaced HEGOS O2 sensor
Replaced Idle Air Control valve
Replaced Air Charge Temp sensor
Still had DTC 13, DTC 42 and DTC 77 codes

I have had Christian Brothers perform the following:
Replace rear fuel pump
Replace mid-ship fuel sending unit
Replace dash transfer switch
CB reported that “The engine surge issue at idle and upon startup is not a fuel delivery issue to the engine, both fuel pumps are operating within specifications.”
They concluded “The issue may be a vacuum issue, a sensor issue or a fuel pressure issue at the engine in the regulator or injectors. Further diagnosis is warranted”

CB then did a Drivability Diagnosis and found the following to be operating according to specifications:
Fuel Pressure
Ignition Timing (electrical)
Intake temp sensor
Coolant temp sensor
O2 sensor
MAP sensor
TPS sensor
Fuel Injectors (electronically)
EGR system
Power and ground points at computer
CB conclusion then was: the engine is exhibiting symptoms of possible valve timing issue, possible mechanical fuel injector issue or possible internal mechanical failure. A running compression test is recommended in order to determine if it is necessary to check the timing of the engine mechanically.

CB then performed a Running Compression Test with the following results:
CYL #COMP / RUN
CYL 1 155 / 65
CYL 2 160 / 60
CYL 3 155 / 70
CYL 4 155 / 65
CYL 5 155 / 60
CYL 6 155 / 55
CYL 7 155 / 60
CYL 8 155 / 65
CB determined that the compression on all cylinders to be within specification and the valves are working according to specifications. The engine is still displaying Valve Timing Issues, Mechanical Fuel Injector issue or engine computer issue. CB recommends the injectors be pulled and mechanically tested.

What I have done since the compression test is fuel up on Chevron 93 octane gasoline. Recent MPG up until then has been 8MPG. Do not know what it is now but by the gauge i would say it is still a low MPG number.
Run ODB1 scan KOEO test results DTC11 all pass
Run ODB1 scan KOER test results DTC 42 & DTC 77 error codes
Engine will idle rough and even die during warm up, idle varies from 500RPM to 1,000RPM, will even surge RPM up and hold steady at 1,200+RPM when driving surface streets at a stop sign. When accelerating from a stop it runs rough and is somewhat lacking in steady power, if I jump on the accelerator the engine performs with lots of power but when slowing down below 60MPH while in Over -Drive the transmission starts to sound like it is confused as to what gear it should be in and unless I shift to 3rd gear Drive I get a jerky motion in the drive train.
Transmission exhibits confusion of gear selection at slow speeds too. I can hear sometimes a slight clanking sound when gears are changing during acceleration and de-acceleration speeds of 10 to 30MPH.
When tachometer varies down to lower RPM range the dash electrical gauge will also lower its reading and then rise again when the tachometer increases RPM. The Check Engine light will occasionally come on and even go off if I am driving a moderate distance at 60MPH or more. It always turns off after stopping and then starting the engine.

Within the last 24 hours the engine has started to be at optimal performance.
Exhibiting steady idle when coming to a stop then accelerating smoothly with horsepower at slow surface street speed range of 10 to 30 MPH. Even better performance in speed range of 35 to 60MPH. Even the clanking of the transmission during gear changes went away when running at this new optimal level.

Although the rough and variable idle issue in not totally gone I am more convinced the issue is electrical in nature more so than mechanical now that I recently have seen the truck run like it did when it was new. I have not been able to find a solution selection on how to resolve error codes DTC42 and DTC77. The reason I lean towards electrical issue is because I see the dash volt gauge vary in sync with RPM when running rough plus the ODB1 scanner says the DTC 42 code is Voltage High Runs Rich which I know it runs rich since the gas mileage is low (8MPG) and at idle the computer seems to be counter acting the running Rich to running Lean then back to running Rich in a cycle of Rich and Lean. However I am more assured the issue is rectifiable since it has started to run normal but not yet consistently.

Could it be as simple as too much Voltage in the system and that is goofing up the HEGOS and yet somehow that has resolved itself?
My eyes are wide open and I think someone in this forum knows what I should be looking towards.

dirtcrew51m

Check all grounds, you might also try looking at some harness connectors for corrosion. Start the truck, start shaking some connectors and see if anything changes.

JSRoeth

Replaced Neg Batt terminal
cleaned Neg Batt terminal leads with CRC
CRC'd and remounted fender Neg Post
CRC'd lower Neg lead on block
CRC'd upper motor Neg lead attached to firewall
CRC'd Emmission Sensors
CRC'd Coil connection
KOEO test creates now / system rich
DTC 42 sensor voltage high
DTC 73 Throttle Position Sensor fault / insufficient Throttle Position change during dynamic Response Test
DTC 25 Knock not sensed during Response Test

I will rerun KOEO again in 2 hours

JSRoeth

I had my Alternator, Voltage Regulator and Battery tested with passing results
I am still getting same 3 DTC codes
DTC 42
DTC 25
DTC 73
I am waiting for a EEC IV Breakout box to be delivered so I can test each component myself.
Will post a reply once I have if nothing else test bad which will lead me to just the PCM as the last thing to suspect.

Maicojames

Any news? I ask as my 95 5.8 just developed idle surge after I flushed the cooling system. Does exactly as you describe 500-1000 a bit at 1200 etc.
Thanks, James

ymeski56

Go back to what the engine is designed & engineered to use = 87 Octane. 93 Octane will create an over rich condition by itself in these stock engines.

Test for proper IAC function Yea, I read it's new. Test for proper function anyway.
See Link: http://oldfuelinjection.com/?p=39

What where the FP psi readings for "at idle" & "at increased idle"?

Are you in fact preforming the WOT test? If not, 25 & 73 would be present.

You have no continuous memory codes?

I would also test Fuel pressure regulator function.
See Link: http://oldfuelinjection.com/?p=41

Also, anytime a sensor is replaced, the battery should be disconnected for a minimum of 5 minutes to clear the kept adaptive memory.

JSRoeth

Now 60% of the time at a street stop it will idle normally then start the idle surging.
I have an OTC 3225 Breakout box arriving today followed by the 1993 Ford F-Series Trucks Powertrain Control & Emissions Diagnosis Manual.

I never received the FP readings from Christian Brothers however i will rerun all tests once my kit has arrived.
I do remove the ground before all electrical servicing.
I just replaced the instrument cluster. Something else was the speed indicator would go erratic at speeds above 60mph. the variable speed sensor has been replaced twice before with little impact. the new instrument cluster improved the motion of the dial to just a steady drop of 10mph then back not nearly as often as with the original cluster. probably another issue yet without a BOB i am a bit blind to truly diagnos and get proper readings throughout.

The WOT results were the first time it never failed to show results yet i can not be certain why is gave a DTC25 thus the reason again for the BOB to test the TPS in place.

no continous memory codes the last time, maybe now since the check engine lit occasionaly appears then will turn off on 30mph surface street driving.

Thank you for the suggestions and the links. i will incorporate them into the next round of testing and hopefully i can shed some postive feedback as to what is happening

ymeski56

You need to realize that at a 9:1 compression ratio, 93 Octane will not ignite in entirety. Leaving residual to progress out through exhaust valve port...& on to a Rich read for the O2 sensor ahead of the Cat.

cgossett

It's a fallacy that high octane gas means more power..

JSRoeth

I ran the 93 octane through only once and did not see any improvement in perfromance.
I did not know the facts about this model of engine that high octane fuel would not burn completely which is good reason to not run that kind fo fuel in this motor besides being an extra expense with no added benefit.

Thank You for the insight about high octane fuel and compression ratio on the 5.0L
I received in the breakout box and now waiting for the Ford PCM & Emmission maunal to arrive.