Folks
Appreciate anyone help/advice here. I have a 1994 4.0 V6 4x4 Manual transmission, Manual 4x4 locking wheel hubs. Its a rare combination.
Truck has always had a somewhat erratic idle, never dropping below 1000 rpm, often between gear changes will raise to 1400-1800, on cold start its 3000 rpm.

Heres whats been done:

• Vacuum system checked, PCV valve, charcoal canister etc all replaced.
• Air fliter change
• MAF new
• Inlet hose changed
• TPS sensor new
• Throttle body re-manufactured by specialist.
• Idle air control valve New
• 2 x HOAT O2 sensors new.

The MAF, TPS, IAC, HOAT are all after market, as good as is available.

The problems persist, i have unplugged the IAC and its behaving a little better but still not perfect.

ECU? not sure whats left? however, to point the finger of suspicion at ECU...when i bought the truck there was a cardboard box and in it was an old MAF, TPS, IAC so the previous owner had been chasing this same problem. In the box is also a spare ECU??? i don't know it this is a replacement or the original removed from the car?

Advice?
Pull the one from the car? is it correct or incompatible? can someone advise part numbers or who can help?
Reflash the one spare i have?
Reflash the one on the truck
Buy a remanufactured one?
Go with a new one and roll the dice it works?

Pictures of "spare" ECU below.

 

HAG0 identifies the ECU as a Ranger/Explorer 4.0. Whether it's the original or not will take more code searching, but i don't THINK it's the original because it's not listed as a MANUAL ECU.
Start here: https://www.grandmarq.net/oldfuelinjection/page17.html

A couple initial thoughts:

It definitely could be the ECU. Although my initial thought is a defective part or just poor quality in at least one of the parts the parts cannon threw at it, I wonder if the ECU was replaced at some point already, and perhaps they replaced the ECU with one from an automatic. What's the code on the one in the truck now? Since we know the HAG0 at least comes from the same engine it shouldn't hurt anything to swap it in and see what happens. (Since it's probably from an automatic, nothing may change.) You didn't show the pins but it looks to be in good shape with no corrosion on the outside, at least.

There are a services (pontisteve/Drag Radial Performance did mine -shoutout!) that can just check the ECU for you, and can also flash/remove the automatic programming too if necessary.

That's a LOT of new parts and these days unfortunately it would be amazing if at least one of them wasn't defective out of the box, especially if they're all aftermarket and not NOS.
Personally I've had terrible luck with new IAC valves, and the fact that things changed a but when you unplug it makes me wonder. I also wonder if the anti-diesel screw (on the throttle body) was messed with at some point, compounding another issue somewhere else, and the computer is trying to compensate. Vacuum leak is an obvious one, but if you say it's been checked and there are no intake leaks, well... triple check!

Good luck!

-A

 

I would say a vacuum leak but you said it had been checked. What IAC did you use? Not saying this is your issue but Hitachi and Motorcraft are the only ones that will work properly. They are true solenoid valves instead of stepper valves. From what I understand these trucks were designed around the solenoid style. Hope you get it figured out.

 

useful info thanks, some food for thought. Several local shops said the same thing about new components, i checked voltages on the TPS and they were all in line, i am unsure how to test the IAC, i'll research that first.

I may pull the ECU in the truck this weekend for comparison.

Thanks for the recommendations.

 

that's helpful, i honestly don't know the brand but am instantly suspicious.

 

IAC Test is pretty easy! KOER, pop the hood and listen to how she's running. Unplug the wiring harness to the IAC. The engine should really bog down and almost die. If it doesn't noticeably bog down, your IAC is the wrong kind/bad out the box, OR you still have a vacuum leak somewhere
Another symptom of a failing IAC is a howling noise, almost sounds like a cow. There's videos out there with the noise in it.
+1 on getting only hitachi/motorcraft, bought mine from RockAuto and haven't had a problem with it since I replaced it for howling!

 

By any chance do you have a Hitachi part number, i cant find anything that matches to a 94 Ranger on the Hitachi store?

 

SO i pulled the ECU, it had identical numbers to the "spare" above. I managed to contact the previous owner who told me the "spare" was water damaged during a heavy rainstorm, he replaced it with a part he pulled himself from a manual 4x4 of the same year.
I can try and get the spare re-flashed but to be honest at this stage im more suspicious of the IAC

I found a receipt from autozone that says the one on my truck is a duralast part? Comments above indicate this is more than likely my problem.

I'll recheck the vacuum over the next few days and keep hunting.

If anyone can identify the Hitachi part number, or a link to anyone who has one id appreciate it.

 

have you checked for any codes. thats a good place to start.

 

yes, i have the OBD1 scanner, it gave i recall 176 and 175 which indicated a problem with HEGO, so i replaced both sensors. They were old and had been in the truck a very long time so may have been independantly faulty.

Doing the IAC test described above whilst engine is cold is somewhat telling. With IAC plugged in at cold its hitting 3,000 rpm and not dropping below 1800 until fully warmed up then its 1400. With IAC unplugged its 600-800 at start up and during driving 1000 to 1200.

This tells me there's no vacuum leaks?

Kind of points the finger at the new Duralast IAC valve.

i'd love to hear from anyone if they have had success with duralast? did i buy a bad one? are they all bad? and if its only hitachi with a new available part can someone give me an hitachi part number? i see several on Amazon that look similar (2 pin etc) but im loathed to keep throwing parts at it.....if its something different.

 

I just thought of this. And actually, this happened to me. The engine temperature never really got up to temperature. I believe that’s 195° and the problem was the thermostat was stuck open. So it took a long time if it did it all to reach temperature And in that case, the idle was always high. The thermostat was brand new and had about 200 miles on it, then it failed so new parts aren’t really good either. Before you’re thinking of changing it figure out a way if you can see what the temperature is after it’s warmed up.

 

Also most test should always be done with the motor at operating temperature 195°

 

idle is almost non-existent at start-up when IAC is unplugged. after it warms up its 1000-1200rpm.

 

so when motor is at temp and you unplug the IAC valve what happens. motor should almost die. or make a change in the idle. i just helped a friend with a ranger, the idle was like 1k to 2k when shifting gears. he replaced the IAC but itwas still there, turned out to be the TPS. i could see that it wasnt working right with live data.

 

Plugged in, engine cold, start up 3000 RPM, unplug rpm=600
Warmed up idle dances around 1800 rpm unless you deliberately pull the revs down with 5th gear and brake, mostly it wants to hand around 1400 to 1800 between gear changes.
Plugged in = High revs, Unplug lower revs.

All seems to point at the IAC. Do i buy 6 aftermarket and randomly try them all? or do i keep searching (four hours and counting now on the internet) for a Hitachi calve that fits a 94 ranger with a 4.0 v6.

Ive been through the entire Hitachi back catalogue and find ABV0034 for the 3.0 V6, but absolute silence from every source on a 4.0 V6

 

[QUOTE=docm;2239599]so when motor is at temp and you unplug the IAC valve what happens. motor should almost die. or make a change in the idle. i just helped a friend with a ranger, the idle was like 1k to 2k when shifting gears. he replaced the IAC but itwas still there, turned out to be the TPS. i could see that it wasnt working right with live data.[/QUO

What scanner are you using to get live data?

 

FYI TPS voltage at idle is 0.84 V, rises to 4.54v with no flat spots along the way. I think TPS is good.

 

Mark 22 Elliott, Unless you happen to just stumble across one the part you need it's going to be real hard to find. Delphi CV 10139 may be the closest thing to Motorcraft that you'll find unless you scour the "net and happen to find one.

 

i use a WIFI / Bluetooth ELM OBD2 Car Diagnostic Scanner and my ipad with an app thats free. pretty easy and lots of live data. youtube has good info on how to read short term and long term etc.

 

@mark22elliott +1 on this, after looking for a pretty good while the only other place you may luck out is finding a halfway decent OEM one in the JY, otherwise go with what you can that is made by a good manufacturer
As to what docm said, I use a BlueDriver scanner. Doesn't have full support for everything on my end, but that's because it's early OBD II, so...
Not sure that there is something like that for OBD I but I could be wrong!

 

I bought and installed a new Delphi CV10139. several comments pointed me to this as the best alternative. Its a 2 wire and looks identical to the Duralast one that was (new) causing above problems.

I'd say its marginally improved. Cold start is 2000 rpm, once warmed up its 1,000 between gear changes, a couple of times its dropped to 700-800 but the truck didnt like it in this cold weather.

It seems like its trying to learn some new settings, i didnt think these ECU's were that smart. I will let everyone know after a week or two of driving.

 

These trucks hold a higher idle during gear changes. It will not drop until the truck gets to 5 mph or under. It pollutes less at higher idle than low idle. It all has to do with EPA emission guidelines.

Has any one ever messed with the anti-diseling screw on the throttle body plate? As you probably know, that is not an idle adjustment screw. There is no idle adjustment. Its all computer controlled.

If its been messed with it will need to be readjusted.

Im sure there's many "threads" that you can search and read through

 

It is a remanufactured throttle body, so all reset to factory.

 

i'd check to see if there is a anti-diseling screw on the throttle body plate, if so, see if its hitting the stop when at idle. if it is back it off a 1/2 turn, see what happens. if its still hitting the stop, back it off another 1/2 turn. im was way out of adjustment.