Help diagnosing random, sudden power loss

I have a recently transplanted 2001-ish 6 liter in a 66 LandCruiser that I'm have had trouble with since the install. At random times, it's like the power goes out completely for a fraction of a second or several seconds - then goes back to running fine.

I've attached a log file. When it does it you can see the (narrow band) O2 go to zero and then the short term trims start to climb - but the engine keeps running the entire time. I have a manual fuel pressure gauge that is showing steady pressure. It is not related to throttle position and can happen at any time. Where do I look? Are the O2 sensors telling the truth? If they are, why is the engine still running. I only sense the loss of power for a very short period of time, but the O2 sensors and trims continue to act like there's no fuel in the system for much longer after that. Are there other parameters I could be looking at that might give me more information?

Peter

Might look at misfires (cylinder mode, current, all 8)
to see if there's any clue about single cylinder issues.
Failure to fire puts a lot of unused air right into the
exhaust and the sensor will see that as big-time lean.
Because it's an oxygen sensor, not a fuel sensor.

Look at net advance and spark retard components,
flaky sensors (IAT, ECT) can move spark a lot, and
fuel as well. In fact I'd log any sensor I could, just
to see what looks like a "fellow traveler" (if not the
cause).

I found a lot of the logged params shown on the
chart display legend, were not showing data. Not
sure why, or what to do about it at my end.

Thanks Jimmy - that's helpful. I'll add those to the set up and see what happens. Which params were not showing up for you? I'll see what they look like on my end.

workingdog,
Probably nothing to do with the problem but your cylinder volume is set for a 5.3L. 8 X 0.75 will get you to 6.0L. Just an observation from a new tuner.

Thanks for noticing that. Now I'll have to get out the manual and figure out how to make that change. The computer did not come with the motor when we did the conversion. They had said it had been updated, but I never really trusted them. At least it wasn't set for a 6 cylinder.

I added the things Jimmy suggested and did another run and they are attached. None of them showed any data at all. The only thing I notice is that the timing is usually, but not always, very advanced.

If I assume the sensors are telling truth (and the fuel pressure gauge in the cab is telling the truth), then it looks to me like a dramatic fuel loss not due to fuel pressure - like the ECM is defueling the engine radically. Is that possible? It feels like limp mode. I don't see any reason to suspect loss of spark?

One of the interesting things is that when it does this, it throws no code.

What I don't get is why the VE table is cut in half?

I see no reason to do such a change, nothing else in the tune is scaled this way.

So, now that I'm seeing the issue with the VE table, I don't trust my tune at all. Who knows what else could be wrong. Should I use one of the tunes in the repository and start from scratch? Or just update the VE table with decent values?

Thats one messed up tune file.
cylinder volume is wrong.
ve is way leaner than stock. maf is richer.
ifr vs kpa vac is way wrong compared to stock.
prndl set to none is going to cause weird problems. Should add the a wire to the proper place on the pcm and have it ground in park and neutral. Set prndl to pn. Among many other things.

What is your injector size? What is your fuel pressure?

I've fixed the cylinder volume issue.

I'll download one of the stock tables on the repository and update the VE, MAF, and IFR vs KPA Vac.

I'll look at the PRNDL - I assume it's set to none because I'm running a 5-speed manual.
I'd love to hear what kind of problems you can have with PRNDL set to none, I googled it and found a lot of contradictory information. Kind of like VSS. I've heard people say I have to have a VSS input to ECM for the engine to run right, and I've people say VSS is completely useless with a manual.

Injectors are new 36 lb. I downloaded a spreadsheet with the correct data (I hope) and updated the appropriate tables (I think).

Fuel pressure is running right at 50 psi.

Peter

Quote:

---

Originally Posted by workingdog

I've fixed the cylinder volume issue.

I'll download one of the stock tables on the repository and update the VE, MAF, and IFR vs KPA Vac.

I'll look at the PRNDL - I assume it's set to none because I'm running a 5-speed manual.
I'd love to hear what kind of problems you can have with PRNDL set to none, I googled it and found a lot of contradictory information. Kind of like VSS. I've heard people say I have to have a VSS input to ECM for the engine to run right, and I've people say VSS is completely useless with a manual.

Injectors are new 36 lb. I downloaded a spreadsheet with the correct data (I hope) and updated the appropriate tables (I think).

Fuel pressure is running right at 50 psi.

Peter

---

PRNDL set to none shouldn't be a problem with a manual, that didn't register when I saw it lol.

Do you have a vacuum referenced fuel pressure regulator? 50 psi is too low in my experience, unless you do have a vac ref fpr and thats with the vac line connected.

As for the vss, you can just look through and find anything that references vehicle speed and tune around it possibly.

Well, thanks for noticing the bad tables. I replaced two (the IFR KPA table looks correct for my new injectors) from stock tunes in the repository and the 'hesitation' or 'bucking' is apparently gone. I'm guessing the tables were so off that at certain points the computer just gave up. Also, the VE was so lean it was causing the highway speed problem.

So thanks so much for the help. I don't think I have a vacuum referenced pressure regulator. I'm going to have to look into that. Something is holding the pressure at 50, I've been through three fuel pumps (2 different people were convinced the hesitation problem was fuel pressure. I now have a very expensive external fuel pump more than capable of meeting the 6 liters needs. But I don't know what kind of regulator there is.

It's also idling poorly, but I guess that's an opportunity to learn about that next.

Are there any speed related tables? I haven't seen any yet. Some say that VSS is only for working with teh Auto trans, but others say it's used in some timing calculations.

Thanks again for the help. Saved me a small fortune.

I learned from my recent 5.3 swap that fuel pressure has more of an effect than anyone on the internet will tell you (I came to the conclusion they don't know).
I started with a typical set up and had 65 psi with a non regulated fuel rail, had a corvette filter/regulator. Ran WAY too rich.
Changed that regulator out to a Aeromotive inline (they say it can be installed inline but it's not ideal) I think it was reducing flow. Had 60 psi.
Got rid of that regulator and went to the junkyard for a fuel rail set up with a vacuum referenced regulator. $10. Now it has 50 psi with vacuum and 62 psi no vacuum, got rid of a bunch of problems right there, like negative fuel trims went very close to ideal.

One thing to know is that a non vacuum referenced regulator has a non-linear ifr table. Vacuum referenced has a linear ifr table (and it way easier to tune IMO (when starting with a non stock build).

very interesting. A little counter intuitive. You'd think that varying fuel pressure like that would make the IFR non linear, but I can see how it might be making life better. Right now, I have no fuel pressure signal to the ECM, is there any advantage to hooking that up?

Having wondered if any tables used VSS, I found one. Throttle Cracker Airflow - speed vs rpm vs airflow - the very thing that would help my idle. So I guess I'm hooking up my new VSS.