Did you check the ground wire to the block?
98 LX470 miss, fuel cut in closed loop only
- Thread starter DrHess
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- Thread starter
- #22
Yes, both the one at the back of the left head and the one on the left side of the intake manifold. Resistance from the intake to the battery negative reads 0.5 ohm, which is about the limit of my meter.
Doesn't sound like fuel to me. If it's not picking up the IGF signal and throwing codes for one bank or the other, sounds like bad wire,ground, or an intermittent short on a connector. Could be on the PCB in the ECU, even. Did you follow the FSM and check the voltages on the wire sending the "I just sparked" signal back to the ECU? Does it throw p1300 and 1305 at the same time, or is it an either/or thing?
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- #24
It throws the P1300 first. It has only thrown the P1305 once, and that was some time after the P1300 and both were set. I went through the book. Not terribly helpful. Replace the coil, check the wires, replace the ECU. The coils have been replaced (one 2x.) The wires are good. I checked them thoroughly. The scope said IGF isn't there when it's missing, so the ECU is correct. As for the voltage on the IGF line, no I didn't check it outside of looking at it on the scope.
Also, as was pointed out to me by white_lx, 1,4,6,7 are all on IGF1 and the rest are on IGF2. It is not left bank/right bank.
It doesn't sound like fuel to me either, but something is causing the coils to not fire, or report that they are not firing. I've checked everything else. The only thing left is fuel.
Also, as was pointed out to me by white_lx, 1,4,6,7 are all on IGF1 and the rest are on IGF2. It is not left bank/right bank.
It doesn't sound like fuel to me either, but something is causing the coils to not fire, or report that they are not firing. I've checked everything else. The only thing left is fuel.
Lots of good and detailed information in your messages.
I don't really see a smoking gun either - you did not miss any of the obvious ones. As per gatormark91, I was thinking some corrosion maybe. IIRC the grounds of the coils are on brackets on the intake manifold and can look pretty corroded.
How about the power to the coils? If there is internal resistance, there could be a problem at higher RPMs assuming the coils have a capacitor built int. But that would not explain why it only happens in closed loop. Since you have a scope, are you able to put an amp-clamp around the coil grounds and see what happens with the currents at the higher RPMs? Maybe also on the injectors to confirm they are not sticking?
You mention it is now also acting up at cold? Does this mean it is also happening in open loop?
I don't really see a smoking gun either - you did not miss any of the obvious ones. As per gatormark91, I was thinking some corrosion maybe. IIRC the grounds of the coils are on brackets on the intake manifold and can look pretty corroded.
How about the power to the coils? If there is internal resistance, there could be a problem at higher RPMs assuming the coils have a capacitor built int. But that would not explain why it only happens in closed loop. Since you have a scope, are you able to put an amp-clamp around the coil grounds and see what happens with the currents at the higher RPMs? Maybe also on the injectors to confirm they are not sticking?
You mention it is now also acting up at cold? Does this mean it is also happening in open loop?
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- Thread starter
- #26
Yes, I think it is happening in open loop now. Although the observations are it happening just after resetting the ECU with a power off (plugs pulled or battery disconnected.) No telling how the ECU is programmed to act before it relearns. Sitting in the driveway in park with a cold motor and revving it up, it starts about 4K RPM, and as it warms up, I think it starts getting lower in RPMs. At first, it didn't do that. When cold, it would rev to 5K without problem, then when it warmed up, 4K and it started acting up.
All the coils are fed off of the same circuit. It looks like Left and Right go to the back bundle for the power. The schematic says the coil packs are all grounded at ED, which is supposed to be at the back of the left head. On the back of the head, I only see one ground wire going to the firewall and nothing else on the head. I may have to split the harness and trace them out. There was some corrosion on the bracket for pulling the motor on the left intake where the ground goes. I pulled the wire off and cleaned it all up, reassembled with oxguard. No change.
I don't have a clamp probe for my scope. I might be able to rig something up with wires wrapped around the ground. I'll have to experiment. Not sure if I could tell a sticking injector from the wave pattern. If the ECU turns it off, current will stop if the injector is stuck on or not, I think. I did consider bad injectors too. Plenty of Sea Foam has gone through them.
All the coils are fed off of the same circuit. It looks like Left and Right go to the back bundle for the power. The schematic says the coil packs are all grounded at ED, which is supposed to be at the back of the left head. On the back of the head, I only see one ground wire going to the firewall and nothing else on the head. I may have to split the harness and trace them out. There was some corrosion on the bracket for pulling the motor on the left intake where the ground goes. I pulled the wire off and cleaned it all up, reassembled with oxguard. No change.
I don't have a clamp probe for my scope. I might be able to rig something up with wires wrapped around the ground. I'll have to experiment. Not sure if I could tell a sticking injector from the wave pattern. If the ECU turns it off, current will stop if the injector is stuck on or not, I think. I did consider bad injectors too. Plenty of Sea Foam has gone through them.
- Thread starter
- #27
Resistance between the coil pack ground pin and the negative battery terminal is below the threshold of my measurement capabilities. Still have no idea where it is grounded to the motor, but it is solid.
Fuel pressure: The regulator seems to be indexed to the intake big box thing over the right head. I would have thought they would index it to the manifold pressure. I put a vacuum gauge T'ed in at the FPR line and there is virtually zero vacuum there, regardless of throttle. It's basically at atmosphere pressure. OK, you can do that. I do it that way on my wife's Sportster. You just have to adjust the fuel maps accordingly. Putting the vacuum gauge on the port at the front of the intake, after the throttle body, shows plenty of vacuum, in the 20PSI range at times. Anyway, fuel pressure is pretty darn solid at 42 PSI, regardless of RPM. Where it is missing, it bounces around a little bit, but no big variations, only a PSI or two at the most. The injectors are also holding pressure well after everything is turned off, so no leaking/dribbling is going on. That's as far as I got tonight.
Fuel pressure: The regulator seems to be indexed to the intake big box thing over the right head. I would have thought they would index it to the manifold pressure. I put a vacuum gauge T'ed in at the FPR line and there is virtually zero vacuum there, regardless of throttle. It's basically at atmosphere pressure. OK, you can do that. I do it that way on my wife's Sportster. You just have to adjust the fuel maps accordingly. Putting the vacuum gauge on the port at the front of the intake, after the throttle body, shows plenty of vacuum, in the 20PSI range at times. Anyway, fuel pressure is pretty darn solid at 42 PSI, regardless of RPM. Where it is missing, it bounces around a little bit, but no big variations, only a PSI or two at the most. The injectors are also holding pressure well after everything is turned off, so no leaking/dribbling is going on. That's as far as I got tonight.
Just some random thoughts:
Maybe it is worth checking the signals to the fuel pump ECU, especially pins FPC and D. See attached document as well as some interesting information here: The Toyota Fuel Pump Control ECU Function | Identifix
How are the fuel trims now at lower RPM's and at the higher RPM's? Are they both positive? Or only at a higher RPM? And both banks?
If the problem occurs at any time now, it may be easier to find. Is it possible that the problem only occurs when hot and is not related to the RPM and or open/closed loop status? This video might provide some inspiration of an injector that fails when hot (same model year as your vehicle btw.):
Maybe it is worth checking the signals to the fuel pump ECU, especially pins FPC and D. See attached document as well as some interesting information here: The Toyota Fuel Pump Control ECU Function | Identifix
How are the fuel trims now at lower RPM's and at the higher RPM's? Are they both positive? Or only at a higher RPM? And both banks?
If the problem occurs at any time now, it may be easier to find. Is it possible that the problem only occurs when hot and is not related to the RPM and or open/closed loop status? This video might provide some inspiration of an injector that fails when hot (same model year as your vehicle btw.):
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- #29
That was interesting. He's looking for the flyback on the injector coil. I can do that. I think he could have diagnosed that with a mechanic's stethoscope or a screwdriver on his ear, but much cooler with the scope. I'll dig my scope out again, and I only have one channel. Also, that darn air box resonator in the way on this motor (and 1UZ's, too) makes it hard to get to the injectors on the right.
Pretty sure the fuel pump line goes up to the underhood diagnostic connector. I can check the voltage there, however, given the stable fuel pressure on the rail, I'm going to assume that everything up to the injectors is fine.
Pretty sure the fuel pump line goes up to the underhood diagnostic connector. I can check the voltage there, however, given the stable fuel pressure on the rail, I'm going to assume that everything up to the injectors is fine.
- Thread starter
- #30
Also, Freeze Frame Data is on page one. I'm not sure what OLDRIVE means., but I don't see anything that jumps out at me.
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- #31
Put the scope on the injectors I could get to, like in the video. They all had a good flyback pulse. And every time the ECU dropped the voltage (grounded the injector), there was a pulse. However, I could see the ECU not firing the injectors when it was missing. And it looked like that on all the injectors I tried, 1,3,5,7,8. Couldn't get to 2,4,6 under the air box.
2001LC
SILVER Star
More I read your thread, the more it seems electronic issue. By this I mean not hardware like fuel injectors, coils, plugs, vacuum lines, gaskets, t-body, etc. More like senor, relay, ECM, wiring, etc.
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- #33
My thoughts were electrical as well, but everything reports/displays as being fine. I have also put new: Coils across all 8, with a new #1 twice, 4 O2 sensors, plugs, sprayed copiously around all vacuum lines and the intake manifold to heads, inspected the wiring, traced the wiring back to the ECU, checked grounds, looked at the injectors with a scope, looked at the IGF signal at the ECU with a scope and probably more. I think I could have swapped a motor in the time I've spent diagnosing this. Borderline same expense, and I'm not sure it would fix it. I'm going to swap my snows off and bring it to the dealer. First time in 25 years I've had to outsource a problem.
One last thought: Is there a chance that capacitors failed on the ECM? Some of the early LS400 (till '97?) ECM's have this problem. That could explain the seemingly randomness.
Please post the dealership's findings and good luck.
Please post the dealership's findings and good luck.
2001LC
SILVER Star
I did read where you replaced all those parts. One thing that was just a little concerning is the non OEM or OE parts like coils. But can't see that causing your issue anyway, so doesn't matter
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- #36
Yes, the replacement parts were a test. Except for the spark plugs, which were "the good ones." Had any of them fixed the problem, I would have swapped it out with a proper NippoDenso part. None of them made any change. I'm stumped, and that's not easy to do.
What problems do people have when the ECU is out? I can get a used "refurbished" ecu for about two bills.
What problems do people have when the ECU is out? I can get a used "refurbished" ecu for about two bills.
2001LC
SILVER Star
I'd not throw any more parts at it. I'd take to Dealership and have them test it. I'd meet with mechanic, but not say much, just listen.
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- #38
Alternator.
I recently read something on a Tacoma forum that sounded a lot like your problem. The guy threw parts at it to no avail. Finally he removed his catalytic converters and found one of them to be mostly melted.
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- #40
I considered that, but with post cat O2 sensors reading fine, I figured they were OK. I had parked it while I worked on other things, got sick with the Chinese virus last October (months before it was supposed to be here), and had to do 2 Lexus V8 timing belts, then went to look at it again and the alternator was frozen solid. By the time I had the alternator in my hand, I figgered I was 1/3rd the way to a full timing belt job on it, so went ahead and did that one too. After putting it back together, a few ECU resets, a new muffler (old one rusted out) and it's running great now. Pulls to 5K RPM then shifts. I think everything helped a little, but I'm blaming the alternator. I think at higher RPM's it was getting noisy and freaking out the ECU. The ECU was definitely pulling the "fire" signal from the coil packs. Saw that on the scope.
