Progress Thread for Troubleshooting Idling/Stalling Problem
 

For those of you that have seen threads about this problem in the past, and/or read my "Questions on KOER Test" thread last week, I'm putting this thread together as an attempt to organize and troubleshoot the following problem. I can't remember the years on everybody's truck that's been having this problem, but my truck is a 91 F-150 XLT Lariat.

Symptoms: [On my truck these occur at operating temp]
1) Truck will hesitate and/or stall when gas pedal is pressed [such as when beginning to accelerate from a stop light], be it quick or slow- it is particularly a problem during spring and summer when the days are hot
2) Truck will idle sporadically after running for a while, is turned off and then turned back on a few minutes later

If you re-read my post in the above link, I want to point out that my description of the revving at idle was not accurate. The other day I tested the problem and found that the idle revs between 300-500 RPM, and it takes about 10 minutes of sit time before idle will return to normal.

Now, there are a lot of suspects for this problem, both electrical and mechanical, as has been discussed in previous posts. As any good mechanic will do, they need to be eliminated one by one. My personal belief is that this is an electrical problem, and so that's where I intend to start. Please keep in mind that altho some of these components may not be suspect at all, I want to be as thorough as possible here, so even the most unlikely suspect will be checked.

Potential Causes:

Electrical
Ignition Coil
Ignition Module
Manifold Absolute Pressure {MAP} Sensor [This is what my truck has, yours may have a Mass Air Flow {MAF} Sensor instead]
Idle Air Control {IAC} Valve
Throttle Position Sensor {TPS}
Intake Air Temperature {IAT} Sensor
EGR Valve Position {EVP} Sensor
Electronic Control Unit {ECU}
Fuel Pumps

I believe that is all for electrical. But please, if I'm missing anything, feel free to suggest it. There are some standard tests and checks I plan to do before I get into testing the above components, which include:

1) KOER Test
2) Run Mode Spark Test
3) Start Mode Spark Test
4) Stator Assembly and Module Test
5) Battery state of charge
6) Inspecting wires for breaks and cracked insulation
7) Inspecting connectors for tightness and corrosion

On to the mechanical suspects. Again, even if it doesn't seem a likely suspect, I'm trying to be as thorough as possible. These are:

Mechanical
Distributor Vacuum Diaphragm Advance
Fuel Pressure Regulator {FPR}
Checking for any and all vacuum leaks, including checking canisters for weak vacuum and checking upper and lower intake gaskets for leaks
Injectors [Pulse Width]

I believe that is all for them. But again, if I'm missing anything, please say something. I'm naming suspects off the top of my head and from what I'm finding in my service manual, but I've never been all that focused when it comes to reading. :D

I'm hoping to begin my testing this weekend, if not sooner, and I will continue to update you guys as I test and eliminate each suspect. I don't expect to have it all done in a day, especially with winter approaching very soon, but every chance I get to work on it I'm going to do my best to get it done.

Let's hope this leads to some answers this time. :)

KOER Test Results
 

I tried posting yesterday but as Diesel Brad posted- FTE seems really slow this week.

So anyway, I got the chance to perform a KOER test yesterday [Friday] and the results were... well, weird.

For starters, I ran the test 3 times, and each time came up with different codes. But then maybe it's because I was tired when I did the tests- twice I got 413 & all 3 times I got 825, both of which are non existent codes. Once I got 513, which is supposedly a CM code to indicate "Failure in EEC processor internal voltage."

It's possible I was just so tired that I miscounted the blinks, but either way it was only flashing 2 codes.

I guess it doesn't really matter. I've decided to go ahead and buy a code reader for it- I looked them up online and O'Reilly has a universal reader for about $30- that's not going to break me. I should have that in my possession later today and with any luck I'll be able to test again today.

On an interesting note, however, or at least what I thought to be interesting, is that during the test, the engine was revving, from about 300 up to 1000 RPM- much higher than when it revs normally. Maybe this is considered normal for the test, but I don't see why it would be and I didn't see anything in the steps about it being a normal thing. So I'm curious if this has something to do with the TPS being bad, and grounding out the STI somehow made it more obvious.

I don't know- but we shall see.

Alright, so I got my code reader. Maybe the pansee way out but I don't really care- if I ran the KOER test 3 times and still couldn't get the codes right, I think I needed it. :D

So according to the manual for the code reader, both the KOEO and KOER tests needed to be performed to determine a problem. Okay, no biggie- I ran the KOEO test today and I'll do the KOER test tomorrow when I get up to my parents house and can use my dad's timing light to make sure the timing is correct.

The results of the KOEO test were:

KOEO: 111 system pass
CM: 172- HEGO circuit indicates system lean
634- Transmission Manual Lever Position Sensor circuit out of self test.

So I guess I'm just a little curious as to what exactly I'm supposed to do about these codes? If they're continuous memory that means they are constant problems, yet I can't really adjust the richness of the air/fuel mixture and my tranny is auto.

Thoughts?

That's all I have for now- I'm going to check the base timing while at my parents tomorrow so I can run a KOER test to see what that produces.

In reference to the tranny code: Think I remember somebody here ( Conanski? Know he's usually good at answering questions ) that meant it wasn't in neutral during the test. Don't trust that, my memory has been known to lie before.

DTC 634 indicates the TR sensor is out of Self-Test range when the gear selector is in Park.

Possible causes:
--Transmission Range not in Park during Self-Test.
--Misadjusted linkage.
--Open or short in harness circuits.
--Damaged TR sensor.
--Damaged PCM.

On the 172 code:
Have you checked the fuel pressure for the lean code?
This can be caused by low fuel pressure from the fuel pumps.

Thanks for the replies guys- I will look into them asap. As far as the MLP code goes, according to fordfuelinjection.com, if I'm reading the steps right, the tranny either has to be in park or neutral with the parking brake set or the wheels blocked, so I just left it in park. Maybe next time I'll try leaving it in neutral with the wheels blocked and see if it makes any difference.

For now I have to focus on the timing. I attempted to use my fathers timing light, but the problem is that it is [most likely] older than I am. :-X14 And after so many years of existence and use, the light on it is so dim you can't even remotely see the timing mark with it. So I'm going to have to check around to see if anybody has one I can borrow. I know my uncle does but trying to coordinate schedules with him is a biotch. O'Reilly has them for about $40 but I'm not willing to purchase it just yet- and they don't rent them either.

I'm thinking that the base timing is off though. According to the emission decal sticker under the hood, the timing should be set at 10* BTDC, and with the tranny in neutral the engine should be idling between 650-750 RPM. Well, the engine idles at about 450 RPM, regardless whether it's in park, neutral, or if I'm waiting at a stop light. Well I know the idle speed isn't a concrete indicator that the timing is off, but for obvious reasons I need to confirm whether the timing is right or not.

I'll update you guys once I find a light to use and make sure the timing is correct.

You also need to remove the SPOUT jumper when setting the timing.

Thanks for the tip.

Well I found a timing light. I was buying a new ax at Harbor Freight last night and the thought crossed my mind to check if they had timing lights. Whaddya know, they did- for $15! Sure it's cheap, but using it even once, it will have paid for itself. Besides, it's not like I'm running a shop here.

Anyway, I'm just waiting for it to get a little more daylight out before I go give it a check. Hopefully it's not too far out or at least if it is, it won't take too much to get it set right.

Alright, so now the timing is set correctly. I couldn't say for sure how far off it was because, as you can imagine, the timing marks aren't easily readable. So I just darkened the 10* BTDC mark which is where it's supposed to be and set it that way. And yes, I did make sure to remove the SPOUT connector while I was doing so. I am curious tho- how much is the timing supposed to change once the spout is reconnected? Because it did change but I couldn't say for sure how much- if I had an idea about where it should be after reconnecting the spout, I could make a couple of more marks and double check just to make sure it's good to go.

On an interesting note, though, as soon as I began rotating the distributor to correct the timing, the engine started revving in the same manner as I described. So now I'm starting to lean towards the problem being in the ignition circuit.

With the timing now set correctly, I can do a proper KOER test tomorrow- I'd do it today but it's getting too dark out and I'm scared of the ghosts. :D

Edit: By the way, something I forgot to check but just did- correcting the timing did not change the idle. It's still revving between 300-500 RPM and when the idle steadies out it's at about 450.

Just a thought here. But I thought I remember reading somewhere that the truck has to be at a certian idle to do the timing correctly. I am not certain. I am about as smart as a sack of sh*$ when it comes to some of the electronic and timing problems. Good luck on the whole adventure I am going through the same thing on my 89.

Grif,

I think you're taking a very methodical, logical approach--and I'd say you read just fine! :-X04 (You write pretty darn coherently, too! LOL)

Are you working from the factory shop manual, or an aftermarket one? (I'm betting you're using the factory one.)

IF you're not progressing, after you pull all the codes you can, you might want to think about the following: a failing fuel tank selector valve can starve the engine, and cause it to do several weird things.

For instance, has your engine temp gone up abnormally, especially at idle? I had some of the symptoms you had, when the fuel selector valve on my '88 F-150 went bad. It was leaning out the engine so badly that it almost got into the "hot" zone while I was just trying to keep it running for like 15 min., in a parking lot--and my truck always ran "low normal," even when pulling a boat in the summer. Yet when the tank selector valve was failing, the engine would idle down waaaaay low (so low the tach would quit registering) but not die everytime, and other times it would spike up to about 1,700. It also bucked sometimes, and stalled at lights a lot. Also, when trying to restart, it would crank forever, firing very infrequently and, again, once it started running, it was running so slowly that I couldn't hear it or feel it sometimes, but if I hit the starter--ZING!--I learned it actually was running, as the starter buzzed the flywheel. Very disconcerting....

The intermittent high idling (up to 1,700) may have been due to an unrelated binding throttle body valve, which occurred at about the same time, but the bad tank selector valve is something to think about. IOW, if you have dual tanks, try switching and see if that changes anything.

And keep in mind that the tank valve can actually refuse to switch, despite you using the switch on the dash, so that the only way to do it is to manually switch the four lines on the fuel tank selector valve body. I did this, successfully, (on the side of the road in a cloudburst--and yes, it sucked :-banghead) when the one tank ran out of gas, and the valve refused to switch, stranding me. I got it going by switching them, and I did not damage the lines, but be careful. The lines are stiff plastic and I feared I would cause them to snap or split, so be forewarned, if you try this. But if you switch the lines and there's no change, you'll know that it's probably not being starved by a bad tank selector valve.

When my truck was starving for fuel, the exhaust smelled bad--different from normal, sharper, somehow. Ungood. (I know those descriptions aren't very helpful, but just take note of any weird exhaust smells that would be consistent with the lean code.)

Have you checked the fuel pressure yet?

Better minds than mine will soon get you going, I'm sure, but your low idle reminded me of the weirdness I experienced, described above.

Good luck!

Big Six

Vancouver- there's nothing on my emissions sticker or my service manual about the timing needing to be set at a certain idle speed. But then, I'm pretty sure the idle is controlled by the computer, and can't be manually adjusted anyway. Maybe on older models you can, but I don't think it's possible on mine.

Thanks for the encouragement BigSix! I'm actually using an aftermarket [Chiltons] service manual. I've always had good luck with Chiltons and they're usually cheaper than factory manuals.

Anyway, I appreciate you posting the multiple problems you experienced on your bad selector valve- it's interesting that it caused similar symptoms. I'll keep it in mind but at this point in time I don't think it's the problem. I fill both tanks when I fuel up and they switch just fine, or at least seem to. Engine temp maintains very well [hangs right around "N" with little variation] whether I'm just driving or pulling a load, and I haven't noticed any funny smells coming from the exhaust- tho I haven't checked either. I can do that once I get it warmed up for the KOER test today.

I guess I skipped out on the TB as a mechanical suspect- tho I guess it was kind of covered with TPS and IAT sensors on the list. I did have intentions of pulling it apart and cleaning it, but that was going to be a "tinker" project, not something to do while trying to diagnose this problem.

I haven't checked the fuel pressure yet. I'm in the process of locating a FP tester I can use- but I intended to do so if I got far enough to check the FP regulator. So that's in the works too.

Thanks for the replies gentlemen, and I'll probably have an update soon with the results of the KOER test.

Holy garbonza beans, Robin! The Batmobile has some problems! Begin synchronization of the hellsinky smash rod stat! Readjust the muffler belt, and fill the tires with summer air!

:-dancing1

But it's probably not as bad as I think. I got a total of 6 codes, and I don't know if it makes any difference, but I'll list them in the order they were displayed on my code reader.

412- Cannot control RPM during KOER high RPM check
172- HEGO shows system always lean [also came up as a CM code]
213- Spout circuit open
411- Cannot control RPM during KOER low RPM check
129- Insufficient MAF or MAP change during dynamic response test
167- Insufficient TP change during dynamic response test

So I guess my starting point would be my oxygen sensor, as code 172 came up in both the KOEO and KOER tests. I've no idea when the last time it was replaced or if it's even been replaced at all. It's the same one that's been in the truck since I've owned it. According to my service manual, it can be tested.

I think codes 129 and 167 would be the next check. My MAP sensor is relatively new [I think it's about a year old now] so maybe that's indicative of a vacuum leak in the manifold gaskets or a line connection. Code 167 may be due to a dirty throttle body which as I mentioned I was intending to clean, but both of these sensors will be given proper testing as well.

I don't think there's much I can do about the 411/412 codes right now as that's one of the problems I'm trying to diagnose. :D

As for code 213, I'm f'ing clueless. :confused: The only thing I can think of is either the connector itself is bad or maybe there's a bad ground or connection?

Anyway, those are the results. I probably won't be able to do any more until this weekend, but I'll do my best- we're still settling in after the move and the wife has plenty of activities planned. :-duel1

I'll keep updating you guys as I continue to get these things checked out.

Edit: By the way, something I wanted to mention. For those who don't know, the KOER test, whether done with or without a code reader, requires the testing of certain things during the test if your vehicle is equipped with them. These being the Power Steering Pressure [PSP] switch, the Brake On/Off [BOO] circuit, and the Overdrive Cancel Switch. [See fordfuelinjection.com for more info] Because of this, especially if you're not sure if your vehicle has these sensors [and I wasn't, so I tested them], it's more handy to be in the cab. If you don't have a code reader, you can be in the cab anyway. But if you have one like I did, you can't operate/read the code reader from inside the cab during the test because the EEC connectors are too short. Now, of course, the manufacturer of my code reader had their special 6 foot extension cord available for sale for this situation. But, unless you want to spend the money on it [I personally didn't bother checking on its price], there's another way to get the code reader in the cab.

First, I determined which connections the code reader needed to make with the EEC connectors. In my case there were 3 connections to be made. My father has a lot of spare wire lying around, so I took 3 lengths of 14 gauge stranded wire. I kept the measurement simple by just stretching them from hand to hand with arms outstretched. On one end of each wire I attached male spade connectors and on the other end I attached female spade connectors. I then taped the wires together at about 12" intervals to make a basic extension cord. Keep in mind that for this application it is only sender wires, so the extra length doesn't affect anything.

I just wanted to share that with you guys in case you needed or wanted the information.

Did you floor it when told to for the dynamic response test?
If I had buddy with the same kind of truck (engine size, transmission and year) I think I would try his computer or get one from a salvage yard before buying all of the sensors.