98 LX470 miss, fuel cut in closed loop only

[DrHess]

Greetings, gents. Long time lurker, first time poster. I have a '98 LX470, ~230K, and when it is fully warmed up and in closed loop mode, at full throttle starting in the low 3K RPM to 4K RPM, I'm getting fuel cut. It won't throw a CEL right away, but it eventually will throw a P1300 or one of the other close by codes, like a P1305. I have a dongle and Torque on my phone. No fuel cut, pulls like a freight train until it is fully warmed up and the long term fuel trims start activating. Then it goes into fuel cut just like a typical Toyota RPM limiter.

I have tried:
New expensive coilpack (best O'Reilley's sold) at #1 when the #1 bad coil code was there. No change, and the next CEL said #1 and #6 were bad. New inexpensive complete set of coil packs and new iridium spark plugs. No change. Two new #2 oxygen sensors. No change. Clean MAF sensor. No change. New MAF sensor. No change. 2 new #1 oxygen sensors. No change. Disconnect battery to clear things and force a re-learn on the ECU. No change. No intake leaks.

I've combed the board here and the rest of the world with my google-fu, which is not weak. I'm about out of ideas.

Suggestions?

 

[DrHess]

The fact that it runs great when not in closed loop seems to indicate that it must be a sensor, but what other sensors could affect that?

 

[ton504]

Look into the fuel pump. Take a look at the short term fuel trims to determine if its running lean.

 

[2001LC]

Question come to mind:
Is this rig new to you and always did this, or a new issue?
Is this while in D going about 80MPH? then flooring it?
Are these new Denso coils, what PN #?
Are you using Toyota, Denso, Aisin parts?
Which iridium spark plugs?
Whats your MPG?
Is this 22 year old relatively rust and corrosion free rig?
Any bluing seen on wires like at battery ground to the fender?
Any signs of rodent chewing wires?
Any water entry in cabin, like windshield leak or sun roof drain?
Ever in a flood?
Has fuel filter ever been change?
Is fuel cap in good working order?
Have you check fuel pressure?
Has fuel pump ever been replaced?
Has fuel pressure regulated ever been replaced?
All vacuum lines inspected and making good seal?
Any vacuum leaks?
Air filter good and no obstruction in air box including in fender well?
Have you hook-up to tech stream and checked for penning codes or recorded during this shut off?
Have you run through a diagnoses tree checking wires, sensors, relays, ECM, etc..?
Any throttle body issues?

If all this stuff checks out. Consider taking to Toyota Dealer and have them diagnosis. A large shop sees 50 to 100 vehicles a day. Speak with mechanical in the shop, whats his experience level. This may save you time and money.

 

[DrHess]

Thanks for your comments.

Is this rig new to you and always did this, or a new issue?

I've had it about 2 years now. It started a few months ago and has gotten progressively worse. Used to only do it over 4K rpm. Seems to be creeping lower.

Is this while in D going about 80MPH? then flooring it?

It does it in neutral, park, or driving down the road when the RPM's get over 3500-ish, regardless of gear.

Are these new Denso coils, what PN #?

Current coils are not Denso. Original coils were Denso, probably came with the truck. The first single replacement was a Beck Arnley, I think. I would spend the thousand dollars-ish to replace the coils if that would fix it. I am not convinced, given that there have now been 3 different coils at #1 and it still complains.

Are you using Toyota, Denso, Aisin parts?

In general, I do, but for diagnostic purposes I put some inexpensive sensors in. No changes.

Which iridium spark plugs?

NGK 4589

Whats your MPG?

Typically 14.5. If I really take it easy, 15. U.S. gallons.

Is this 22 year old relatively rust and corrosion free rig?

Relatively. There is some rust, but relatively rust free.

Any bluing seen on wires like at battery ground to the fender?

No.

Any signs of rodent chewing wires?

I've seen no signs, and I've look over the harness pretty well. I've had fewer problems since the Global War on Squirrels started.

Any water entry in cabin, like windshield leak or sun roof drain?

No.

Ever in a flood?

Not that I know of.

Has fuel filter ever been change?

Yes, did that first. No difference. Also note that before closed loop, there is no problem at all.

Is fuel cap in good working order?

Yes.

Have you check fuel pressure?

Have not checked. Again, it works great when cold.

Has fuel pump ever been replaced?

Not that I know of.

Has fuel pressure regulated ever been replaced?

No.

All vacuum lines inspected and making good seal?

Yes, they look good.

Any vacuum leaks?

No. Went around EVERYTHING with some carb spray looking for leaks. Nothing.

Air filter good and no obstruction in air box including in fender well?

Filter is good. Haven't looked in the fender well beyond what I could see looking in the filter box.

Have you hook-up to tech stream and checked for penning codes or recorded during this shut off?

Looked for pending codes. None. I have not tried recording with tech stream during the problem.

Have you run through a diagnoses tree checking wires, sensors, relays, ECM, etc..?

The FSM says to replace the coils, check the wires, replace the ECU. I've done the coils and checked the wires. If you have a better diagnosis tree, I'm open for suggestions.

Any throttle body issues?

None that I know of. It looks pretty clean in there.

If all this stuff checks out. Consider taking to Toyota Dealer and have them diagnosis. A large shop sees 50 to 100 vehicles a day. Speak with mechanical in the shop, whats his experience level. This may save you time and money.

I hate to admit defeat, but unfortunately, that was where I was leaning. The fact that it runs great before closed loop indicates to me that things like the air filter, fuel pump, regulator, throttle body, injectors, etc. are functioning properly. The computer is making it miss, probably with LT Trim (which I observed is negative at the problem), then complaining that there is a miss and cutting fuel. The FSM says that if a coil issue is detected, it does fuel cut. Watching the LT Fuel Trims with Torque Pro, when they are not active (open loop), everythign is great, then closed loops starts, LT Fuel Trims start having values and it starts missing.

 

[2001LC]

I really feel you need to see if any pending DTC and read freeze frame data as issue occurs. Recording live data during incident may prove too be very helpful.

If you looked for pending codes in a OBII dongle, like a blue tooth with phone app. Those don't show near as much as a TOYOTA hand−held tester or hooking up with a mini cable, at least mine doesn't.

Any work performed on this 98LX shortly before this began, like say a timing belt job or anything?

A few comments

1. NGK IFR6A11 are recommended by FSM. You've IFR6T11 Which should be okay, but not spec.
2. Set of Denso coils (non Toyota branded) can be found for under $500. You've both non standard plugs and coils. These are probably fine. But it's a slipper slope when we deviate. It makes saying "I know those are in spec" impossible!
3. If o2s replaced are non Denso, the slope is gets slippery.
4. Make sure you've no nest blocking air intake in fender well.
5. Heat increase electrical resistance. So don't count out fuel pump, just because works fine cold.
6. * Resistance for crank and cam sensors change with heat. **
7. I ask about water entry, rust, corrosion, bluing on/in wires because as corrosion of wires and connection increases so does resistance. Old electrical system benefit from the "BIG THREE". Low amperage to ECM, coils and sensors can produce issues. Like running a drill on a 200 ft 18 gauge extension cord, the drill will eventually burn up.
8. I wouldn't consider it throwing in the towel (admitting defeat) to seek help from dealership. These guys see this stuff day in and day out. It could save you a lot of time and money.

This is different than your issue, but worth mentioning. It was an issue with fuel pump. We'll never know why it couldn't be detected. But fuel pump replacement corrected it.:
"This 06LC with 194K had a CAT replaced, bank 1 ((IIRC that's DS (drive side)). Following history from Dealer records I found PO complained of engine dying while ascending I-70 into the Rocky Mountains. As he approached the Eisenhower tunnel about 50 miles west of Denver at tree-line 12,500 ft ASL, the engine would die (limp mode). He'd let it sit for awhile and it would then start. He reported this on more than 4 occasions. The Toyota Dealership, Stevenson, tested fuel pump (45 PSI) and reported as good, with no DTC. Toyota shop mechanic took on test drive up to the tunnel with fuel PSI gauge hooked up, along voltmeter to fuel pump. They found no issues at 39K miles. At 96K miles P0400 DTC, BANK 1 CATS. CAT was replaced. At 97K miles Dealer replace fuel pump even though it tested in perfect working order at 39K and at 97K miles, nor could they duplicate engine stall issue. But for some reason Dealer keep coming back to fuel pump. Finally they replaced the fuel pump. Issue(s) did not reoccur again, over next ~100K miles.

​

 

[DrHess]

OK. I'll dig my laptop out and hook it up with Techstream. I'm not sure how to record with it, but I'll play around and see. Last time I hooked it up, there were no pending codes, just the code for coil #1. It's going to take me a couple days to get to it. While changing the oil on my RN Truck last night I found the center link was about to fall off. That could be a problem. I replaced it only 190K miles ago, when it wore out at only 190K miles. They just don't make stuff to last anymore. Good thing I got the one with the lifetime warranty.

The first (upstream) o2 sensors in there were nippodesnso and did not look very old at all. They were probably replaced just beforeb my purchase of the vehicle.

No work was done to it just prior to this starting. I replaced the plugs when I got it 2 years ago. They probably had about 8K miles on them. I think the last thing I did before that was the back drive shaft U joints some months before this.

As for the cold/warm thing, it starts acting up immediately when it goes into closed loop. No when it's getting close, or a little after, or at different times, immediately. Like, everything is fine, run it up to 4K with no miss, long term fuel trims start having values and it goes into fuel cut at 3500.

 

[jerryb]

I was thinking injector, temp sensor, coolant sensor, maf etc.

but once you get to + 22% or so on fuel there would be a check engine light. Can you do something to make it run in open loop?
there isn't a CHT sensor that I know of. Cam sensor, crank, timing belt weirdness.

I guess maybe I'd run a hose with a gauge up to the windshield, although by the time you gear up to do that you could just buy another pump. There's no easy way to see delivery pressure under load.
I've bought a pump from oreilly before until i found the right denso and then returned the oreilly one. COsts zero money to throw that at it. just thinking.

these don't have an over rev fuel cut do they? RPM limiter? you know,, bouncing up and down with the pedal pegged? seems not likely for either at 4000rpm

 

[87warrior]

I'd suggest loading the Torque screen with as many sensor inputs you can read. Take it for a drive and watch the Torque gauges. When the miss occurs, you should see something peg or drop in value. At the very least you should be able to get a better idea of what is actually happening. This is when a better (expensive) bluetooth dongle shines as it sends data much faster than the cheaper units.

 

[DrHess]

I've done that with Torque, looking for what's going on. Near as I can tell, the long term fuel trim is the main thing that looks out of place. It drops when the fuel cut hits.

Yes, these have a RPM limiter, and it is fuel cut. That is, it drops the fuel pump relay out in a pulsing fashion. That's what I am experiencing when this happens. And it only happening in closed loop is the strange part. And it will happen sitting in the driveway in park. I guarantee that the fuel pressure will be low when it happens, as it is the ECU dropping the pump out. I don't think that will tell me much. The factory service manual, which I have, says it will go into fuel cut when it detects a misfire. Plus, just before closed loop, it will rev past 4K and pull very strong.

What I suspect is happening is that the ECU is thinking the motor is running rich, reduces the fuel, which then causes a misfire, which the ECU interprets as a coil problem and cuts the fuel pump. But, why does the ECU think the motor is rich?

 

[DrHess]

I had a chance to play with it this afternoon. I'm not real sure where to go in Techstream, but I was poking around in test something or other, AFM or something, and playing "One of these things is not like the other... Three of these things are kinda the same..." (which got me through 10 years of higher education,) I found:

O2FT B1 S1 -1.6%
O2FT B2 S1 0.74%
O2FT B1 S2 99.0% <-- This is not like the others.

So, what does 02FT B1 S2 mean?

Where/what else in Techstream should I be looking at/poking? There were no codes, and despite the misfire when I stepped on it in park, the misfire counts were all 0.

 

[2001LC]

I'm looking through a few screen shots I have pictures of, and don't see that O2FT B1 S2 , just may not have taken picture of. But I think it's O2 fuel trim bank 1 (DS) sensor 2 (rear).
Could be a bad O2 bank 1 (DS) sensor 2 (rear).
Also watch for miss fire under load, while giving gas, foot on brake, in "D".
I find if I do a "heath check" first, most all live data will come up in the screen.

 

[DrHess]

I've had 2 different sensors now in all 4 O2 sensors, including the rear driver's side one, with no change in the problem. Also, I get readings from all 4 sensors, and they vary, not fixed. I did a health check before that screen. I'll try again. My "talk to the cars" laptop is an old XP one, and getting screen caps off of it is a bit challenging.

 

[white_lx]

P1300 and P1305 indicate a missing IGnition Feedback signal - IGF. Those are signals from the coil packs to the ECM indicating a successful spark. Two sets of 4 coil packs are combined into a single IGF signal, This is done to save wiring, as the ECM knows which cylinder was firing, so it only has to confirm that a spark occurred.

According to the wiring diagram the first set of signals are packs #1, 4, 6 and 7 and the other set of signals is #2, 3, 5, 8. So surprisingly they are not split between L and R cylinder banks? I'm assuming one set is P1300 and the other one is P1305.

If misfires are detected, the ECM will switch off the injector of that cylinder, which might be interpreted as fuel cutting maybe?

It could be that there is a problem with the IGF signals making the computer think that there are misfires. Or there could be actual misfires happening. Are you able to look at the misfire counts? Here is a screenshot what to look for in Techstream.

 

[DrHess]

Yes, I've looked for a misfire count. It is 0 across all 8. What I don't understand is how the ECU can be happy with the IGF signal until the motor warms up, then it's not happy.

 

[DrHess]

Fiddled with it more this evening. Kept my foot in it until the CEL (MIL) came on. Here it is before:

Here's the CEL and Freeze Frame:

 

[DrHess]

Post CEL:

 

[DrHess]

Electrical connections on the IGF circuit for 1,4,5,7 are good, and good to the ECU. I broke out the oscilloscope and put it on the IGF1 pin of the ECU and had a look. The reason the computer says there is no IGF signal on 1 or 6 is that when it is acting up, there is no IGF signal. At idle and at, say 2K RPM, nice even blips down on the scope. Rev it up until it is missing and you can see the IGF signal is dropping out for some of them when it misses. The miss count never goes over 0.

Next up, did a compression test. Cold, unfortunately, as it is a royal PITA to pull the plugs. I think if I pulled them, the motor would be cold by the time I got to them all anyway. Results:

Pressure (PSI)	Cyl	Cyl	Pressure
185	8	7	185
190	6	5	180
190	4	3	210
190	2	1	180

That 210PSI on #3 is the only outlier. Whatever that is doesn't fit with the other symptoms of a misfire in 1,4,6,7.

It is now doing it when cold too, but not as bad as when hot. Also, the CEL (MIL) will flicker when it misses.

 

[DrHess]

Also, the plugs had maybe 200 miles on them, probably less. Subjectively, plugs 1,4,6,7 had more soot on them than plugs 2,3,5,8, consistent with the ECU biatching about not firing.

 

[DrHess]

So, what's left? Fuel pressure? That's next on my list. I have a gauge somewhere and a banjo adapter I made about 20 years ago for a MR2. The banjo bolt should be the same. I'll see if I can dig it out, otherwise buy the HF kit for $90.