Motor idles normally, and on low throttle runs fine.

Push the gas pedal down and immediate coughing, stalling.

Codes P0351...6 (exceeded the display on my phone; presumably went to 8) which is "Ignition Coil A Primary/Secondary Circuit" (substitute in B thru H, I guess).

It is like the module that drives the coils has gone weak.

A couple of days ago I left the ignition in the Accessory position and drained the battery to the point it would not crank. With a full recharge it seems happy now, though.

Alternator dying?

 

It looks like it is indeed a weak alternator. Voltage is 13.2 at idle but drops once the speed increases at all. I suspect the ECU makes the spark hotter when throttle is opened, which drops the voltage down further, or the low voltage makes the spark unable to bridge the spark plug gap.

 

yes, its possible that it is a dying alternator if charging voltage is under 14v.
One way to check would be to clear the codes, then have it jump connected to another vehicle whose engine is also running. If your symptoms don't happen and codes don't come back, then you will have your answer.

 

Thanks, good suggestion.

I changed the alternator (had a spare on hand). Voltage is up and stable (13.8), but the errors are still happening. Bummer.

Curious thing: It is only erroring on cylinders 1-6. 7 and 8 do not appear.

 

Now this is getting weird. Voltage climbs, up to 14.2 now. Does a new alternator need to bed-in the brushes to achieve full voltage?

The catastrophic misfire mode with full throttle continues.

 

A logical next step would be to swap the ignition coils from 7,8 to 1,2 and see if codes follow. If it doesn't, then swap the wires too.
if still doesn't, then it could be distribution box/ecu (I might not be correct on my terminology here) that sends the signal.
you didn't do any recent work, that could have pinched 1-6 wires, right ?

For now, I think we can assume it's not alternator problem as that should have affected cylinders 7 and 8 too.

 

Thanks. No, didn't touch any ECU related wiring.

The alternator had a broken terminal connector on the regulator, so I removed the regulator in an attempt to repair. Unsuccessful, I reinstalled the regulator. Possibly the brushes need to re-seat.

I opted to get a Bosch remanufactured alternator because I had to wire tie the regulator connector in place; I have to guess sooner or later it would fail.

The ECU will shut down spark in ways that can be difficult to predict from the outside. The fact that the voltage is still odd, starting out at 13.8 and then rising to 14.2, suggests there is still an alternator issue.

I would suspect a battery problem, but cranking is vigorous.

 

Swapped a new coil in for #5. Same fault.

For the moment I think I just have to sit and wait for the new alternator - although this one is humming happily along at 14.2 volts.

Could it be the dying alternator killed the ECU?

 

I forget but do you have DAS?

running a load test in DaS will tell you if it’s good or bad and may give you a code or two from the ECU - a smoking gun would be an inability to interrogate that module.

seems like you have swapped the coils with no code following so that points to ecu but you should clear your charging system first.

 

No DAS but I do have the Autel, which is able to poke pretty deep. "Motor Electronics 9.7" and "ISM". The codes that are thrown are from Motor Electronics, which I assume is the ECU? It's hard for me to imagine the ECU partially failing, but I have been surprised before.

I was also wondering about the fat wires going to the alternator. Supposedly those crimp connections have a way of corroding or whatever, developing internal resistance. This would act like a weak alternator. I could check them with a multimeter.

I put a voltmeter on the 12V line while the motor was running and watched it through to the failure. Stayed solid at 14.2 and then collapsed with the failure, which involves rpms dropping to a stall. Don't know what to make of that.

The failure is only throttle based, not rpm. It can free run 000's of rpm, but try to get there suddenly - rev the motor - and it goes into shutdown.

I want to change the alternator to the Bosch anyway, so while I wait for it I may test the cables and take a look at the other spark plugs. The #5 was a bit crusty but nothing terrible.

Thanks, and any other ideas, let me know. This is a head scratcher.

 

Also, what does the "Load Test" do? The Autel has a Full Throttle monitoring but it seems kind of light. There is no way this thing would survive going anywhere full throttle anyway.

 

The load test is a guided test where you gradually vary the electrical load of the vehicle and graphically monitor the alternators ability to keep up with the amperage draw.

 

Thanks. I wonder what it uses to increase load. I turned on the high beams, that's about 200W out of about 2,500W total available. The voltage sagged modestly, about 0.1V.

 

Rear window defrost is actually the alternator killer / load cliff iirc.

 

I ran a manual load test, monitoring the voltage with varying electrical loads. I was able to get everything on except the cooling fan. Voltage drops to ~13.5.

I suspect the primary cable is bad - the connections have resistance at the lug on the alternator. With the electrical load on, the lug gets HOT.

Note with resistive connections, the situation downward spirals - the resistance rises as it gets hotter, and if the system pushes harder on the connection. I may try repairing the cable by dumping solder into the crimp. Note the connection at the firewall did not get hot, so there is something special about the one on the back of the alternator. Perhaps because the starter current flows through there as well.

Also, I thought of a reason cylinders 7 and 8 are not error coding. Those two are last in the firing order. It could be the ECU errors out and shuts down cylinders 1 through 6 and by the time it gets to 7 it figures it ought to leave a couple of them running.

 

GROAN the cable is attached at the top of the starter. I don't want that badly to pull the cable. After installing the new alternator, and seeing if it remedies the situation, I'll check the voltage drop across the cable.

If there is voltage drop across the cable I think I'll just install a parallel cable to the post at the firewall. Or cut the terminal at the alternator and simply replace the cable, leaving the segment going to the starter in place.

 

Autel has the alternator load test. It indicated low voltage with new alternator in place. I did not complete the test (checking voltage at various positions) because a test of the voltage from the alternator positive post to the firewall lug showed a voltage drop: 0.15V at a minimum, >0.5V with load. Assuming it is running 100A, that is 0.005 ohm, which corresponds to about 12 gauge wire. Almost certainly there is significant resistance in the lug.

Ordered a four foot 4 ga cable to replace the alternator positive cable. I'll cut the battery side off the double-terminal lug at the alternator.

The battery is also probably bad. With it disconnected, the voltage sagged overnight to 12.3V. This is remarkable considering it is a name brand (Interstate) and is only about a year old.

The failing alternator (and cable with resistance) probably contributed to its weakness, but this seems a little extreme. It was never drawn down to zero, just low voltage once recently. It is disappointing; batteries used to be these no brainer decisions.

The battery and the alternator work together; one can bring the other down, so if either is weak, you can end up with a perpetual cycle of destruction. This is like fixing a leaking air bag, only worse.

This is in line with users' comments that weak battery can bring down the ECU.

The six coil errors appear in the firing order. I still do not know for sure that getting the charging system right will fix the problem, but it needs to be done.

Moral: Check your alternator primary cable, and do not replace the alternator without carefully verifying the battery first.

 

Installed the supplementary positive cable in parallel. Boosted the system voltage to about 14.4V. It was losing.1 to .5 volts.



Now the charging system is 100% - but the problem still remains.

I am starting to wonder if it is bad gas. I had been doing partial fills at a dive gas joint in town, so I could get ethanol free. But they don't get a lot of traffic. The throttle response definitely is like what a friend encountered with bad gas; it just won't take throttle.

Possibility is still ECU, but - there are no DTC's short of really struggling with it. Whatever is happening, the system is not recognizing as a problem until it gets really bad.

Plugged fuel filter?

 

Just let er idle to empty and put in good known gas. Problem maybe solved; if not then ECU.
And do remember to perform the Italian tuneup after idling to empty.

 

ty bro, this is maddening but (a) I am fixing things that needed fixing, (b) getting used to walking, and (c) learning that there are people who will loan me their car without my even asking. It is humbling.

I bought a can of super duper octane boost (there are lots of hot rodders around here!), on reading that loss of octane is one of the main things that kills gasoline in storage I can't tell if it's better now.

Is there a good way to drain the tank besides running til empty? Sadly the tank is at 96%; 25 is a lot of gallons of gas to get rid of.

I am having a hard time believing that it is the ECU because it won't throw codes until the situation becomes dire. It can go all limp mode stumbling, die, and then restart without any codes. BUT the stumbling / limp mode sometimes remains until I leave it shut off for a few seconds, which really sounds electrical, or maybe it's the gasoline inside the cylinders needing to evaporate. Because it won't throw codes until the situation is dire, I cannot tell whether the codes are an artifact of the terrible running during limp or reflect the root cause.

 

Suck out the gas with a topsider vacuum tool, like the oil? I don’t know if there’s a drain - or just break the filter or pump connection at the tank.

 

I believe I have learned from this forum that there are two tanks, so even if you pull out gas from one, half of it stays in other tank.

Hopefully Eric can find a drain or something underneath to drain all the gas.
it might be just easier to let it idle.

 

Bah, you can't even get a tube down the filler neck.

The thing was hard to start this morning (two attempts), then ran briefly, then stalled and refused restart for a while. Managed to get it back running. It is now idling like nothing whatsoever is wrong.

ECU showed #0120 P0336 "Tooth space on sensor rotor termporarily not detected or wire fault"

Again, difficult to tell whether this is a code resulting from the engine struggling to live, or the root cause itself.

Plugs were a crusty with light brown deposit. I was planning on changing them soon anyway; might just give them a try. Note I had been doing a lot of short trips with very light throttle, barely enough to warm up completely if at all.

 

While you are running it idle to get rid of all the gas, consider adding this additive to the gas. It has PEA in it and helps remove deposits along the way

https://www.walmart.com/ip/16888906

 

Yes, there are two fuel tanks. The system reports the pressure difference between the two.

Changed the spark plugs. Fortunately it probably needed to be done; the Bosch plugs had widened the gap considerably and had eroded ground electrodes. Unfortunately, changing the plugs did not help the problem.

There is what looks like a flare nut fitting where the fuel line goes to the rails on top of the motor. It shouldn't be too difficult to rig a fitting to that, connecting to a hose. Presumably I can get the fuel pump to run continuously without the engine running. Run the hose out to the driveway and borrow gas cans from anyone and everyone to hold 98 liters of gas.

Almost makes me wonder if changing the ECU should be done first.