m60b40 missing, low idle, back firing

[JGood]

Thanks man! PM sent.

[Jean]

PM me your address I can mail you my 404 to try.

[JGood]

Yeah, I welded up a bunch of the leaks, it made no change.

I measured the voltage on the signal wires of the o2 sensors, they are putting out .50-.70 volts. They should fluctuate between .1 and .9 from what I understand, and staying on the high side of .45 is rich, staying on the low side of .45 is lean. So I'm apparently running rich (which makes sense, the fuel pressure is low at idle). But why doesn't the ECU correct that, and add LESS fuel, to lean out the mixture?

I verified I'm getting battery voltage to the o2 heater wires.

I also noticed that I'm no longer getting lambda or o2 codes, or any codes besides "CAN message" (canbus?) and a purge valve code (I have no purge valve, and the vacuum port is plugged).


Summary of the current (major) issues:

-With o2 sensors unplugged, car idles dead steady at 500 rpm's, has full power, and runs great overall, except the on/off throttle transition, it's jerky and feels like the engine is slow to respond.

-With o2 sensors plugged in, I can start the car, it will idle at about 500 rpm but will go up and down the tiniest bit, maybe 50 rpm's. It will do this for hours without any major stumbling. When I give it a little throttle, and it struggles to rev. I give it a lot of throttle and it revs perfectly. As soon as I leave off the throttle though, it goes down to idle, and will either immediately shut off, or rev up and down from 400-1000 rpm's a few times, then shut off. I restart it, steady at about 500 rpm's again.


I've replaced/checked every sensor, seal, gasket, hose, nut, bolt, and clip in the entire fuel injection and ignition system. Only thing I didn't try is a new ECU.

[RobertK]

Just had a light bulb pop on in my head while sitting at work.

I have exhaust leaks before the o2 sensors. I can feel them "puffing" out air at idle, but I bet they also suck in air on the reverse side of the pulse wave. Oxygen going into the exhaust, THEN past the o2 sensors, will tell the sensor it's running way lean. It richens the mixture to compensate, but it makes no change. It keeps going richer, but that fresh air is still coming in. The fuel pressure is dropping because of how much fuel the injectors are dumping. The car runs rich as hell (which would explain the black smoke when revving) and starts dieing. The lambda control codes get set off because the DME realizes it can't adjust the mixture enough to reach 14.6:1.


I'm pretty confident this is the issue. Now I need to pull the engine to remove the headers so I can properly weld them. Lol

FWIW.. When I was finishing up my S50 swap I had a huge exhaust leak where my downpipes connected to both of my headers and my O2 sensor was inches from fresh air and I never got a CEL for fuel mixture or O2 issues.

[Jean]

:)

[JGood]

Just had a light bulb pop on in my head while sitting at work.

I have exhaust leaks before the o2 sensors. I can feel them "puffing" out air at idle, but I bet they also suck in air on the reverse side of the pulse wave. Oxygen going into the exhaust, THEN past the o2 sensors, will tell the sensor it's running way lean. It richens the mixture to compensate, but it makes no change. It keeps going richer, but that fresh air is still coming in. The fuel pressure is dropping because of how much fuel the injectors are dumping. The car runs rich as hell (which would explain the black smoke when revving) and starts dieing. The lambda control codes get set off because the DME realizes it can't adjust the mixture enough to reach 14.6:1.


I'm pretty confident this is the issue. Now I need to pull the engine to remove the headers so I can properly weld them. Lol

[JGood]

Pulled the intake manifold tonight. Replaced the TB gasket. All gaskets are now new, except for head gaskets. No change though.

Guess I'll try to smoke test it. If the CCV is bad, that won't really show up in a smoke test, will it? Unless maybe I pulled the dipstick?

[JGood]

Just hooked up a vacuum gauge, I'm getting 16 in/Hg at idle. It goes up to 20 if I slowly rev it to 2-3k. It will spike at 22 if I leave off the throttle at those RPM's. It dips down to zero if I snap the throttle open at idle.

I know nothing about what should actually happen, does that sound right?

[JGood]

New discovery.

The car only stalls when the o2 sensors are plugged in. If I plug them in, I'm getting Lambda 1&2 and o2 1&2 codes. It stalls often when they are plugged in. My fuel pressure at idle also drops down to 47 or so, as opposed to the 50 that I should see.

If I unplug them, I get no codes, and the car won't stall. It still feels a bit weird as I transition to on/off throttle (at any rpm), it acts like a bad TPS switch. And it obviously runs rich. But it holds 50 psi fuel pressure at idle.

o2 sensors are brand new, and are installed in the exhaust approximately right at the rear of the transmission.


I replaced the fuel pump and fuel pressure regulator. No change.

[RobertK]

Alusil. I really don't think it's a compression/wear issue... the engine makes amazing power, and pulls from 1k to 7k under full throttle without a single glitch. It's just the on/off throttle transition below 2k that feels weird... it's acting like it has a bad TPS or a vacuum leak or something.

I would still test compression to be sure. Other things can affect it than the type of block you have.

If you've been driving a M20 E30, even a M60 with lower than normal compression will be strong on the butt dyno.

Its a simple test and will give you one of the most important pieces of information regarding the health of your engine.

[JGood]

Would anyone with a running m60 mind taking ohm readings on the ICV while cold, and while at operating temp? Both of my ICV's ohm out to spec (12 ohms at 1&2, 12 ohms at 2&3, 24 ohms at 1&3) when cold, but when installed in the car, with engine up to operating temp, they basically double in resistance, which doesn't make sense, and seems like it would cause the issue I'm having.

I cleaned both with brake cleaner. They were both stuck to the point where I had to use a screwdriver to pry them open and closed while soaking in cleaner to get them free. So I may have possibly ruined both. They still work to a point, as I do here them snap open/closed when I unplug/plug them in, and it also effects the idle when I do so.

One of them was stuck in the nearly closed position (~500 RPM idle, and it acted exactly as it does now), the other was stuck in a pretty far open position (~1200 RPM idle).

[JGood]

Gaskets are new. No access to a smoke tester. Already swapped in a known good MAF, no change.

[Jean]

Are the intake gaskets all new? Can you do a smoke test?

Is the MAF known good from a running car?

[JGood]

The problem seems to be isolating itself to an idle and throttle on/off issue. Today I drove the car, and every single time I left off the gas, it shut off. It starts right back up, idles dead steady at 500 RPM's, then I give it gas, and it will run all day without missing a beat, until I leave off the gas and let it return to idle, it just shuts off. It does it 75% of the time.

I checked fuel pressure, getting 3.25 bar at idle and 3.5 bar when revving. Spec is 3.5 bar +/- .1 bar. I watched the gauge as the car shuts off after revving, pressure jumps from 3.25 up to 3.5 as it dies, then stays at 3.5. I assume this is ok? That's like 3 PSI off from spec.

I also swapped o2 sensor banks, no change.

Also swapped ICV's again, no change. I did notice something interesting though. When the car is sitting there, up to temp, and I shut it off, if I check the ICV resistance immediately, I get way high numbers ( like 30, 60, 30). If I let it cool down, they drop to normal spec (12, 24, 12). Both of my ICV's do this, so I assume it's normal.

I also sprayed carb cleaner around every sealed area I could find in the intake system, and got no surges at all.

Also installed a new OEM coolant temp sensor, no change.



Guess I'll wait for the Peake scanner to arrive.

[JGood]

True Corey, I haven't tried the spray test yet, I'll do that.

I'm going to try swapping the o2 sensor connectors tonight (I'm not sure which one goes to the left bank, and which one to the right bank). If that doesn't make a difference, I'll be doing the fuel pressure test. If that looks good, I should receive my scan tool tomorrow, and that should answer some questions.