m60b40 missing, low idle, back firing

[Jean]

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

Is the MAF known good from a running car?

[JGood]

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

[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).

[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]

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.

[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]

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 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

[Jean]

:)

[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.

[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.

[Jean]

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

[JGood]

Thanks man! PM sent.

[RobertK]

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

I've got one too if you need it.

404 is also OBD1 which I thought was before CAN bus.

Do you have the CEL code number?

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 really hate to sound like a broken record and I sincerely hope that I am wrong but it really scares me how you've just about described everything I experienced when I first installed my S50 (O2 sensor didn't make a huge difference). You're engine might be at the threshold of healthy compression on all but 1 or 2 cylinders. In my case I had 1 very unhealthy cylinder @30psi, 2 unhealthy cylinders @65~70psi and the rest were 95~120psi.

Even have a video of the low idle while the engine hunts to raise idle and when we rev it and slam the throttle shut it either shuts off or do the low~high fluctuation which got worse as the engine warmed up.

Do you have any videos are starting and idling it? I will try to find mine for comparison.

I know what its like to bang your head against the wall trying firgure out the little stuff when you are in the home stretch but do that compression test if even just for peace of mind. I avoided it for 2 days trying just about everything else just because I didn't want to know.

[JGood]

I've got one too if you need it.

404 is also OBD1 which I thought was before CAN bus.

Do you have the CEL code number?

Code 210

"CAN Interface, Trans. Intervention Version DME"

I really hate to sound like a broken record and I sincerely hope that I am wrong but it really scares me how you've just about described everything I experienced when I first installed my S50 (O2 sensor didn't make a huge difference). You're engine might be at the threshold of healthy compression on all but 1 or 2 cylinders. In my case I had 1 very unhealthy cylinder @30psi, 2 unhealthy cylinders @65~70psi and the rest were 95~120psi.

Even have a video of the low idle while the engine hunts to raise idle and when we rev it and slam the throttle shut it either shuts off or do the low~high fluctuation which got worse as the engine warmed up.

Do you have any videos are starting and idling it? I will try to find mine for comparison.

I know what its like to bang your head against the wall trying firgure out the little stuff when you are in the home stretch but do that compression test if even just for peace of mind. I avoided it for 2 days trying just about everything else just because I didn't want to know.

It really doesn't exhibit any symptoms of bad compression. Maybe I'm not doing a good job of describing the problem. With the o2 unplugged, it runs 100% perfect, except for a slightly jerky transition from on throttle to off throttle, and vice versa (at any RPM). If it wasn't for that jerkiness, I'd leave the o2's unplugged and say screw it. I did a 5th gear 1500 RPM pull, it makes awesome power even that low. It spins the 235's in 2nd gear and idles at exactly 500 RPM's, dead steady, all day. I could take a video, but a picture of the gauge with the needle sitting at 500 rpm's would be the same thing. It doesn't budge. I've left it idle for like an hour without a single blip or hiccup.

It only totally transforms to a shitty idle only when the o2 is plugged in. It has to be a mixture issue.

I'll test it for the hell of it, when I get a chance.