91tpiwrangler

No, there are no logs attached as the forum won't allow me to attach the file type.

Pro

Youll have to zip it up. Thats what I do.

91tpiwrangler

Alright guys, I appreciate the help from everyone who is contributing to this thread immensely, but lets drop the crap and get back to the issue at hand, my shitty running jeep!

The IAC passage on this throttle body makes a deafening sucking noise which makes it extremely obvious when its open. It has always opened for a few seconds after starting the jeep, but will usually close just after.
I can certainly tell that it is going wide open when the truck is about to/is surging.
I don't want to give any illusions that I know what causes what to **** the bed on the ECM side. All I can tell you is the IAC opens and the BLMs plummet.

Correct, the jeep ran one day, but hasn't run since then. I did check the FPR diaphragm and it was fine.

You guys are starting to loose me here. The throttle blades are barely open at idle, just enough to set idle rpm speed.

YOU HAVE NO IDEA HOW FRUSTRATING THIS IS! Normally, I run a small angled K&N cone filter directly on the TB. For all of this, its been off and the TB has just been open to the engine compartment, so I find it hard to believe its a lack of air. I can force the IAC closed by grounding out the diag. port and when the motor finally dies from the surging, when I cut the key off I can hear the IAC closing, so I feel confident the IAC is functioning properly.

Great, thanks. They are all stored on my work laptop so I cant upload anything tonight.


I received the new ECM today, swapped the prom over, and then threw it in the truck. I think it runs worse at this point than it did before.

I decided to ohm out the o2 circuit wires and make sure there were no breaks/ excessive resistance in them. Everything showed good on the meter. Then i decided to check voltage again. This is where things got interesting. When I backprobed the ECM o2 signal wire i was getting 12V! I thought something was wrong with the meter so I shut it off and checked again, but it was still 12v. I then went to the connector side and checked voltage, but was only getting .5v. I went back to the ECM and it showed 12v again! (at this point I was about to loose my mind). I pulled the o2 harness back up the firewall and held the length of it in my hand while checking voltage on the plug end. I found that if I bent the harness close to the connector, I could cause the voltage spike! I cut all the heat shrink off the connections and discovered the 12v heater wire wore though 2 layers of heat shrink and contacted the .54v signal wire for the o2!
ULTM8Z, you were right, there was an issue with the o2 circuit! At this point, I was feeling pretty good that I had FINALLY found the issue. I pulled the harness apart and isolated the wires, hooked the o2 back up, and fired up the jeep. It ran ok for about 10 seconds, surged twice pretty harshly, and died. I then unhooked the o2 and restarted the jeep. It ran OKish for about 30 seconds before surging and dying.
So, what are the chances the 12v supplied on the signal circuit fried the o2?

ULTM8Z

That's great that you finally found the root cause!

The reason the IAC is wide open and sounding like a vacuum cleaner is the ECM is doing it's best to keep the engine alive.

It's possible the O2 got fried. I'm not familiar enough with the internals to say one way or the other.

It sucks that you'd probably have to buy yet another O2 sensor to test this...

There's also the ECM to think about as well, but the only thing that makes me think the ECM is ok is the fact that in open loop, it seems to run ok (according to the data and what you describe).

TP has the gauge set up such that the maximum voltage to display is 1200 mV. However, the maximum I ever saw was 1092 mV. Again, certainly no expert here, but maybe there's some circuitry in the ECM that clamps the voltage so as to protect the ECM?? Maybe someone like Rbob or 84Elky or one of our other gurus knows... Hate for you to have to buy another ECM!

91tpiwrangler

I was very excited to finally find something that was actually incorrect!
I ordered another o2 sensor, so we'll see. (hopefully the last $40 sensor ill have to buy...)

I'm really hoping the ECM didn't bite the bullet during this. The only hope I have is that after I found the issue and corrected it, the ECM sensor voltage dropped back down to .54v.
I found the attached image online while tracing the o2 circuit. It appears to me, the ECM probably supplies full voltage (not sure if 5v or 12v) to the signal wire, but it passes through a resistor to drop voltage to .54v. Hopefully if its 12v prior to the resistor, there wont be any damage done by back feeding 12v through it.

Street Lethal

iTrader: (16)

Wrangler, the image you posted in the first post shows something entirely different than what you are describing. The blades are honestly irrelevant at this point, as the commanded RPM is based on certain parameters. If the blades are open, the IAC closes to meter the commanded air. If the blades are closed, the IAC opens to meter the commanded air. Simple. Your IAC shows a rise in steps during cold start Open Loop, and this is based on the image you posted. The O2 is irrelevant at that point because the loop is not closed yet in terms of feedback when the IAC deviates. I'm glad to hear you checked the diaphragm in the regulator as that can be an issue when the engine sits for awhile, it will dry up. As far as the O2 sensor, you stated on the first page that you replaced the O2 sensor with no apparent effect. If you still feel it is the O2 sensor, then why didn't you force Open Loop to see if that is indeed the culprit and inspect how the engine runs ignoing its' feedback? Don't see how an ECM will go bad just from sitting unless there are critters around, but anything is possible. If that is in fact the case though, you might want to consider upgrading to an EBL system...

- Rob

91tpiwrangler

Attached are the logs I've collected.

ULTM8Z

Street, not sure if you've read through all the posts... but this is the summary that got him to this point....

I had him disconnect the O2 a while ago and take data.

The thing that convinced me something on the O2 sensor circuit was wrong was the fact that even with the O2 disconnected, TP was still reading 1092 mV (which would ordinarily be impossible). As you say, in open loop, this doesn't matter since the ECM ignores the O2 in open loop.

The way it got into closed loop at all with the O2 disconnected is that the 1092 mV voltage that the ECM is seeing on the O2 circuit is substituting for what the O2 would normally send. Since it sees a voltage and the coolant temp enable temperature is met, it goes into closed loop.

In those logs, Wrangler would report that the engine would run fine for a while and then stumble and die, which would correspond to the log... where I would see the engine run stable in open loop and then as soon as it reached closed loop temperature, the ECM would recognize the O2 voltage coming in from (what we now know to be) that short to 12V on the O2 sensor harness.

Once it got into closed loop, the Integrator would immediately plummet to 108, chasing the O2 voltage. The BLM would then plummet to 108, and you'd see the idle speed and IAC going crazy until the engine died.

91tpiwrangler

I understand the relation of the IAC and the throttle blade position. What I don't understand is why the ECM thinks the airflow is inadequate and constantly opens the IAC until the motor dies (if that is the real issue, I don't know)

Yes, the o2 isn't considered a diagnostic device until closed loop, but surely telling the ECM its receiving 12v would raise some sort of flag for the ECM, correct?

By forcing open loop, I assume unplugging the o2? It will randomly run for 30/45mins when it feel like it. From a dead cold start it seems to run normal until the 3 min mark, when it jumps to closed loop and everything goes to hell.

When I had the injectors and fuel rail out, i figured it was a good time to check the diaphragm.

I can find no trace of mice or anything of the sort having gotten into any of the wiring.

Assuming this is what EBL is (http://www.dynamicefi.com/EBL_P4_Flash.php) I dont think i really need that level of tunability. I may throw a mild cam and heads on the motor down the road (if it ever works correctly again!) but still dont know if the custom ECM is necessary.

ULTM8Z

Basically the ECM is getting confused and ends up fighting itself..

It's detecting a false mega-rich condition (a constant 1V on the O2 is basically pig rich to the ECM). So it's pulling fuel out like crazy until it reaches the limit of it's "trim-ability" at BLM of 108. So the engine is getting starved of fuel.

At the same time, the ECM is seeing the engine RPM dropping due to lack of fuel. But it still thinks you're running rich since the O2 is still pegged at over 1V. So it does it what its supposed to do to keep the engine alive and opens the IAC to give it more air. But without the fuel, it doesn't matter how much air comes in through the IAC... without fuel, ultimately dies.

The logs showed it was somewhat of an intermittent short. I forget if I mentioned it in this thread or over e-mail, but at times the voltage would be 450mV (the normal stoich voltage). But anytime the voltage was shorted up to 1092 mV, it spelled trouble.

91tpiwrangler

So anytime the short applied 12v to the o2, the ecm leans the fuel and opens the IAC in an attempt to fix the issue. If the ecm doesn't take in the o2 readings until closed loop, what would cause it to surge and open the IAC in open loop?

ULTM8Z

From what I saw in the datalogs, I didn't see any surging in open loop.

The reason it was able to go into closed loop at all with the O2 disconnected was because the 12V short was supplying the voltage the ECM needed to see from the O2 sensor circuit in order to go into closed loop.

91tpiwrangler

That makes sense.

91tpiwrangler

I received the new o2 in the mail today and just finished installing and data logging the jeep. Watching the logs, the o2 appears to be working, but unfortunately the motor still won't run for very long. There seems to be overall less engine surging (not completely gone) but more of a engine rpm decline to stall out.
I even threw the old ecm back in to see it it made any difference, but it didn't.

Is there any type of ECM relearn procedure (other than swapping the prom into the new ECM)?

Anyway, I've attached the most recent data logs.

ULTM8Z

Yeah, the O2 sensor circuit definitely seems to be fixed now. ECM appears to be behaving normally for the most part, which would put my fear to rest about possibly having damaged the ECM with the 12V short on the O2 circuit.

Nevertheless, something is dragging the BLM down to 108 still once you get into closed loop though. Not sure what to make of it at this point though.

If there's nothing wrong with the ECM, then something on the side of the engine with the O2 sensor is malfunctioning.

Pro

Is it possible he just has a really bad tank of gas? Im looking at cold start, new ecm, new 02, fixed wiring, no surge, just dies.
Have you checked the EGR? Maybe block it off or make sure its disabled/closed.
Look at the Time between ref Pulses in microseconds. Everytime on a decrease, when its injecting more fuel, there is its normal RPM increase. So whats causing the ECM to want to add more fuel... I saw a document around somewhere with the computer's logic on what triggers it do add more fuel like its doing there.

91tpiwrangler

Are the o2 cross counts correct in the image below? It seems to go sky high before resetting and counting up again.

I found this page (http://www.gnttype.org/techarea/faq/BLMINT.html) that really breaks down the function of the INT and BLM. After reading this, it looks like the INT is operating properly on the "restart with old ecm". The INT fluctuates between 142 and 90 but cant seem to recover the BLM before the motor dies.

Could this be a tuning issue then? Earlier on in this thread you mentioned the running voltage being low and explained the injector "on" length would change with voltage. Now that it running at 14.6v, could this also be contributing to the non running condition?

The o2 is after the Y pipe in the motor, so it sees both exhaust banks right after the union.

91tpiwrangler

I had just filled the tank the day before this issue all started. Its been about a month since, so I think its unlikely (not impossible) the fuel is bad.

I removed the EGR from the motor when it first went into the jeep.

Back to my question for ULTM8Z, would increasing overall system voltage mess up the original tuning enough that the ecm tables are no longer able to compensate?

Admittedly, I did not personally not tune the motor (I had it tuned by http://www.scotthansen.net/ through a series of data logs and burned proms) so my knowledge of the computer language associated with the ecm run program is very small.

ULTM8Z

That's a good thought. You might try getting your system voltage back to the way it was and see if that solves the problem. If it does, then yeah most likely it's a tuning issue related to your injectors.

at that point, it'd be up to you whether you want to keep running it that way or retuning for the correct system voltage. Since you say it ran perfectly before.

what injectors are you running?

edit: by "tuning issue" I don't mean Scott messed up. I only mean he tuned around want seems like a system malfunction (That was evidently unknown at the time). Lol... Something I've done many times myself... and when the malfunction is found and corrected, you have to go back and either start from scratch (depending on the severity) or simply make further adjustments.

91tpiwrangler

I'm headed out there now to pull the alt./battery wire and see what happens.

Ideally I'd just have it re-tuned with the higher voltage.

Bosch III

Sure, I dont blame him at all.

91tpiwrangler

Nope, that didn't seem to make a difference. If anything, it shut off quicker than before from a cold start.

ULTM8Z

Do you know if he tuned the injector voltage offsets?

91tpiwrangler

I don't have a clue. I'd send him a data log and he'd send me a burned prom to data log until he got the numbers where he wanted them. I think we went through 5/6 tunes.

Pro

You dont have like a factory BPJW you can plug in and give a shot?

91tpiwrangler

Pro

The stock prom to control the fuel injection. BPJW is incorrect, I meant AUJP I think. Im mobile away from home right now otherwise I would look it up

91tpiwrangler

Ok, no I dont.
(Haha! I was racking my brain trying to figure out what BPJW was and Google wasn't any help either!)

Merry Xmas everyone!

Pro

sorry for confusion
Do you have a chip burner?
if not, i would invest in these
http://www.moates.net/burn2-chip-pro....html?cPath=64
http://www.moates.net/gp1-package-gm....html?cPath=64
Then burn the factory GM AUJP bin from the moats website or gearhead-efi.com. Then you know youre running factory numbers and not some BS that someone else created for you.

Or if you didnt want to go thru the burning process, which is all inside tunerpro already and i learned in a couple of days when doing my truck to tpi, you could just go ahead and purchase
https://www.ebay.com/itm/90-92-350-T...p/162819374622 and put that in the ECM.

91tpiwrangler

No, I do not have a chip burner.

Im honestly not interested in buying the burner, chipsets, and learning how to write my own command files. I have no issue paying someone to do that for me. I just want to motor to run again.

I have the knock sensor, egr, vss, a/c deleted from the motor. Would a stock PROM work, or would it throw codes since there would be a lot of missing equipment?

91tpiwrangler

Sorry for the long pause. The jeep is outside in a tarp carport and it been in the teens the last few day. Not to mention Verizon has been dong service work in the neighborhood and I haven't had internet for the past 2 days.

I ran a compression test on the motor and was (mostly) happy with the numbers. Cylinder 8 seems to be a little lazy compared to the rest, but not low enough to require a teardown. The plugs did look pretty fouled this time too.

(plugs removed, 4x engine turnover)
1 - 155
2 - 160
3 - 155
4 - 153
5 - 150
6 - 150
7 - 155
8 - 138

Id like to get a leak down tester next and make sure the upper-end is functioning properly.

ULTM8Z

Do you have the air injection smog pump also deleted?

91tpiwrangler

Yes. I'm not sure what all came factory on these motors so I listed the ones I know for certain that were deleted.

Pro

Yes a stock prom would throw codes for egr and knock. Why don't you have a knock sensor anyway? I would give a stock one a shot if it were me unless there was something fundamental radically different inside the engine that's been swapped out that requires a tune.
BTW is the msd ignition box required? Bypass that and retest if not. Maybe that thing is going bad.

ULTM8Z

Agreed.... I'd probably try to isolate the ignition system and eliminate the aftermarket stuff from the equation.

Something went south, either related to that 12V short somehow or coincidentally with it.

BTW, where was your O2 sensor picking up 12V from?

91tpiwrangler

The ecm and harness was originally sold as a standalone kit to control the TPI setup on a SBC motor. I had the hard parts and bought the ecm/harness. I guess they decided the knock sensor wasn't necessary.
The guy I had tune the motor back in '14 said the company I received the original ECM/harness from actually used a modified 6cyl PROM? Scott replaced it with the proper PROM and re-tuned for my motor. I've attached a pic of the PROM I currently have if that means anything to you.

No, under the intake is a stock 350 w/ a set of block hugger headers.

No, the MSD isn't required. I did test the MSD box per MSD's instructions and it checked out fine. It will give me 3 (pre, TDC, post) arcs on the HEI plug tester when the motor is running also. I can try unhooking it, but its not a plug and play box so it will require some rewiring.

91tpiwrangler

I use a 3 wire o2 sensor (heater +, heater -, and O2 signal) The heater + wire contacted the signal wire. They are both direct from the ECM to the o2.

Attached is a pic of the o2 short

ULTM8Z

I guess my question was more of where the +12v ia getting its power source from?

SLEEPER 86

Any luck with your issue?
I have to agree with a previous poster about the possibility of a tank of bad has
I have worked in gas stations for decades and seen water get into the main tanks from heavy rain, as well as coming from the bottom of the delivery trucks tank.
The symptoms you describe are exactly like water in the gas.
The water ***** up in the bottom of the fuel tank and once it vibrates or is pulled to the fuel pickup... cough, sputter, no start.
If you're still having issues, drain the tank as much as possible, re-fill with fresh gas, and add a bottle of red ISO-HEET
I'd hate to see you pulling your hair out chasing all these computer issues if it's just water in the gas!
You could also do what I did and replace all that stone age computer Crap with an even more stone age carburetor, intake manifold, and non computer distributor.
Just think of all the wire you'd be able to yank out and never have to trace again!
My car lost about 12 lbs just removing all the ecm wiring and it originally had a carb.
Not to mention the aluminum intake probably saved another 25 lbs or so.
Anyway, swap that gas out and let us know if it makes a difference.
Cheaper than chasing your tail.
Best of luck! Let us know

moneyman380

Have you found the issue ?