Need some input -> Problem with 3.2 transplant going lean and misfiring after two min

[mysocal911]

Originally Posted by mysocal911

Since it runs smoothly when cold and the mixture is rich, but runs poorly when it warms up,
you may have a poor injector spray from some injectors. You need to remove each injector connector
separately and determine it's effect. You can also pull each spark plug connector to find a missing/weak cylinder.

The key point being made here, in addition to the injector spray, is that you need to eliminate a potential mechanical problem
in the engine, e.g. a weak/missing cylinder (valve seats, valve adjustment, etc.). By disconnecting either an injector or spark plug,
you can quickly tell how each cylinder contributes to the engine's running. All cylinders should have an equal effect on how the
engine idle drops when the cylinder is shutdown.

[john walker's workshop]

Did you pop the airflow meter cap and look at the track yet?

[Wayne 962]

Originally Posted by john walker's workshop

Did you pop the airflow meter cap and look at the track yet?

I didn't take off the air flow meter to take a look at it, but I did test the flapper box using the scope, and it tested perfectly. I did take a photo of the results on the scope - it's on the first page of the thread - I will take another look in case I missed something. I can also retest very easily with the breakout box.

Here's the image again. Basically tested the voltage coming from the air flow meter over time. Pressing on the flapper makes the voltage go up. Letting it close makes it go down. Basically what the factory manual says to check for:



Here's a neat thread on repairing and testing the meter. My scope readout is not as pretty as his is because I had to reach all the way in the intake and open it by hand (so it wasn't consistent). But there are no voltage drops, so I'm 99% sure that the meter is fine. It supposedly only has 65K miles on it, so it shouldn't be bad either way.

Still, I will re-run the test with the scope again tonight (takes five min).

-Wayne

[Wayne 962]

Just retested again. No problems, the waviness is me not being able to stick my hand in there consistently each time.

[FrankM_]

Wayne,

Difficult to see the 'discontinuities' on your scope trace for the AFM. I think the best way to test it for it's IDLE condition is to put your breakout box in, check the regulated power supply to the AFM (should be 4.95V - 5.05V coming from the ECU) and check that it returns a stable 0,24 to 0,25V. Measure while running at idle (measure voltage, do not try to measure ohms with ECU connected).

Here are my values, measured on the bench with the AFM open after re-tracking. I had a 'significant' discontinuity when coming off idle (jumped from 880 rpm to 2300 rpm straight away) and it was relatively hard to see on the traces, had to select the right timescale. When opening you could see it was worn down to the PCB !

Anyways, if it gives you that stable 0,25V output at idle (or 5% of Uin), you are fine for debugging your idle condition. No need to open the AFM for that.

Pin 6 (ECU) = GND for AFM
Pin 9 (ECU) = Reference voltage for AFM
Pin 7 (ECU) = AFM return voltage
Pin 22 (ECU) = AFM air temp sensor

If you want to check the AFM air temp sensor (also easily done without the afm being opened):
- disconnect ECU
- measure the ohms from pin 22 against the pin 6 GND

0°C/32°F : 5K - 6.2K (tolerance 10%)
20°C/68°F : 2.2K - 2.8K (tolerance 10%)
30°C /86°F: 1.5K - 1.9K (tolerance 10%)

[FrankM_]

Maybe another point to check in your list : are you running a 87 chip or an earlier chip (as the ECU seems 87). As Steve already mentioned, the chip programming determines the idle rpm to be used when you are going to reset your mixture following your procedure.

If original :
As of 87 : 880 rpm
Before : 800 rpm

[Wayne 962]

Tuesday update:

Today was a weird day. I'm even more confused now.

Jacked the car up so that I could get a clear thermal photo of the exhaust headers. All six were the same temperature, which leads me to believe there are no particular issues with any one cylinder. When I replaced the plugs the other day, they all looked pretty much the same and fairly good. As I mentioned previously, we had the injectors completely rebuilt and tested, so I have faith that they are functioning correctly too. If we had a bad cylinder or bad injector, then that would show up as a cool spot on the thermal camera (I've used it many times before to check and find issues like dead cylinders on other cars).

The next thing I did was disconnect the O2 sensor from the harness and plug it into the scope to measure the output. I also hooked up 12V to the heater. The O2 sensor was reading a consistent .88 volts which corresponds to a rich condition. This doesn't make sense to me, since the LM-1 wideband O2 sensor tool sticking out of the tailpipe was reading closer to 14.7 at this time. I ran this test and checked it many times, and determined that the O2 sensor was reading correctly. To double-check, I took the LM-1 wideband sensor and screwed it into the O2 sensor bung (on the right side of the car), then started the car up to check the mixture. Sure enough, the sensor was reading a mixture in the low twelves. So, both oxygen sensors (the new one from yesterday and the wideband one from the LM-1 tool) were saying that the cylinder 1-3 bank was running rich. I suppose that yesterday when the car was reading really really lean with the LM-1 sensor, it was because the O2 sensor was reading rich. That part makes sense.

What doesn't make a whole lot of sense is to why the LM-1 tool sticking into the tailpipe is registering a much leaner condition than when it's installed in the O2 sensor bung. I have a feeling that it has something to do with the two-pipe sport muffler, and perhaps one of the sides of the muffler is sucking in fresh air from the outside inadvertently, which is leaning out the mixture. I tried sticking the sensor in the other pipe, and got slightly different results, but this needs more attention tomorrow.

I then adjusted the idle mixture screw so that the reading from the LM-1 (screwed into the O2 sensor bung) was reading 14.7 (approximately). At this point, I thought this would fix the problem - it didn't. The car started to run very poorly again, yet the meter says that the AF ratio is 14.7. I called John Walker at this point and he suggested I head to my friend's shop and have it tested with their CO and HC meter. He said (correctly so), that the A/F mixture will tell you if the adjustment is correct, but it won't tell you about other combustion problems. Still, the thermal camera from underneath the car shows that the intake headers all look pretty even, so I'm not sure if there is a cylinder-specific problem. Perhaps there is something amiss with the distributor, but again, the car runs nearly perfectly during the initial 1-2 minute warm-up and then starts crapping out.

I also checked (on the scope), the injector pulses for both channels. They match what the expected pattern is, as shown in the factory manuals.

As I mentioned in the previous post, the air flow meter appears to be working correctly. Even if it were "stuck" open, then that should make the car run richer, not leaner.

Fuel pressure - I checked the fuel pressure according to the factory manuals. 2.0 bar running, and 2.5 not running (with fuel pump jumpered). In addition, when I disconnected the vacuum line to the throttle body, the pressure increased back up to about 2.5 bar (disconnected). Connected it reads 2 bar. All of this behavior is consistent with what the factory manual states is normal. I of course broke off the little T-fitting at the back trying to pull it off (I felt it was old and I knew it would break!). Part number: 928-573-727-02 if anyone needs it.

I also ordered new OEM Beru ignition wires. This car currently has the Magnecor wires, and I've never quite been happy with the fit of the connectors or the fact that they feel a bit flimsy. I prefer the OEM ones in this case. Maybe (fingers crossed) they will magically fix something there. The current ones are at least 12 years old. I believe that the BERU ones have resistors in the spark plug leads. Not sure about the Magnecor.

I'm running out of ideas. I guess tomorrow I can take out some of the injectors (check to see if the insulators are installed properly), and swap some of them around. When the injectors came back from the shop, they looked completely different (newish). They looked so good that I thought they may have given me someone else's, but I checked the BOSCH part numbers and they were the correct ones.

Maybe tomorrow I will change out / test the cylinder head temperature sensor, or test it when it's warm by putting a paperclip across.

I don't get the following:

- Why the air fuel LM-1 monitor in the tailpipe would read differently from the one in the bung. Maybe getting some outside air sucked in?

- If the readings are / were off, then when I adjusted the mixture properly to 14.7, the engine should have run well at idle.

- If this were truly a spark / ignition problem, then shouldn't the issue be prevalent from startup?

I think I need to sleep on this, a lot of this isn't making any sense. What is really annoying / frustrating is that the engine is running perfectly fine for the first two minutes, which basically rules out any mechanical issues (which is good) and focuses the attention on the fuel injection / delivery.

Thoughts?

-Wayne

Photos:

This shows the reading of .88 volts out of the stock Carrera 3.2 narrow band O2 sensor. I grounded the multimeter directly to the sensor to verify that there weren't any grounding issues:



With the LM-1 Sensor mounted directly into the bung, this shows 12.6 AFR:



Showing the LM-1 O2 sensor plugged directly into the right side (1-3 on the 914) of the engine):



Injector pulse width patterns on the scope - looks similar to the pattern in the factory manuals, and is also identical on both channels:



Fuel pressure of 2 bar while running:



Video of the car running with the LM-1 installed into the right-side (factory O2 sensor disconnected). This is after I set the idle mixture to 14.7. Car runs like crap, as you can see:



Video of the car with the injector pulses on the oscilliscope:

[Steve W]

RC Fuel Injection is a great place, in fact it's the first place I recommend as the go to when owners need their injectors cleaned and tested. However I worked with more than a handful of owners who still had injector problems even after they came back from cleaning with a good bill of health (no particular injector service facility in particular) that only replacement injectors solved. That said you may have an injector on the bank that is not closing completely, or sputtering on low duty cycles, such as near idle, that will cause that cylinder to idle excessively rich or lean, and if it's on the bank where the O2 sensor is, it will send a signal accordingly to the DME of the average mixture of those three cylinders. This I'm assuming your O2 in your exhaust is only reading either the left for right bank. The LM-1 at the tailpipe shows a different reading, because it's displaying the average of all six cylinders. So this is why I previously suggested if there's a suspect injector, to try swap them side to side and see if the car's O2 sensor displays differently. However you've seemed to confirm that left and right bank are different, which indicates there either is an injector problem, which again you can try swapping them side to side to see if the readings swap, or possibly the the left and right cam timing is different. When a cam is retarded on a 3.2, it tends to lean out the overall mixture noticeably. That's not to say there couldn't be an individual cylinder mechanical issue such as a bad valve or spark, but that's getting a bit beyond the basics.

You could try disconnecting one injector at a time to see if you can discern the one cylinder that makes the overall idle behavior different than the other five, but you'd want to do that with the O2 disconnected and the idle control valve also disconnected so they don't try to compensate. A 3.2 idling on five cylinders almost sounds normal like all six firing, so you may or may not be able to detect a difference. You can also observe your LM-1 readings for any differences. You could also check the harness connector for the injectors to make sure there is no corrosion on the pins, as left and right bank are separate at the firewall plug, but common inside the DME unit. Your problems don't initially seem like a faulty DME unit, but if you want to borrow a good tested unit, just let me know.

[FrankM_]

I would start by checking the ground connection of the O2 sensor that is made through the tread?
That's were it is measuring it's 0,88 V against (very very rich condition)?
Is the thread full of anti-seize ? One of the wires for the heater element normally goes to ground point MP XII on the intake runner. Check for a clean 0 Ohm connection between this wire end and the ground point.

Just ruling out any electrical issues with the O2 sensor first.

UPDATE - forget the above, your external O2 sensor has it's own power independent of the car, so the ground connection will not be the issue

[Wayne 962]

Originally Posted by FrankM_

Difficult to see the 'discontinuities' on your scope trace for the AFM.

Thanks for the useful data dump on the AFM. Just to be 100% sure, I will run the tests again on it, moving the vane slower to see if there are any drops in the voltage. It's already setup from last night, so it should be easy. As you mentioned, the AFM is reading low voltage at the start, so that wouldn't be affecting this running / idle issue. At this point, I do not want to remove the meter because I sealed all of the boots (smoke tested before and after), and I'm confident that there are no vacuum leaks. I'm also reluctant to start opening up the AFM and messing with it, when all of the data seems to point to it being okay. I broke the wide-open-throttle switch removing it the other day - any time you start messing with stuff (especially in the tight confines of the 914 engine bay), there's plenty of room for disaster.

I've got new plug wires coming today. I will pick them up later on this afternoon.

As Steve W. suggested, in the meantime, I will remove the injectors (again), and take a look down into the cylinders to see if the problem that John Walker had is indeed the issue. I will also swap the injectors left / right and see what the mixture looks like after doing that.

I forgot to mention that I did spray carb cleaner all over the intake gaskets yesterday - no changes detected in the engine. Spraying some down the air cleaner made the engine rpm increase (as expected). So, there does not appear to be any leaks there.

When I swap the injectors, I'll take the car out in the street and jack it up so that I can check the header temps with the thermal camera. That in the past has been my number one tool for identifying cylinders that are weaker than others. It's best to use the tool when the car is very cold as the differences in temperature tend to even out as the whole engine gets warm. Yesterday, when it was warm, the thermal photos (I haven't posted them yet) seemed to indicate no problems.

Originally Posted by FrankM_

Maybe another point to check in your list : are you running a 87 chip or an earlier chip (as the ECU seems 87). As Steve already mentioned, the chip programming determines the idle rpm to be used when you are going to reset your mixture following your procedure.

If original :
As of 87 : 880 rpm
Before : 800 rpm

Indeed, this new information from yesterday complicates things slightly. When the car was surging (at the very beginning of this mess), I jumpered the test port and set the idle to be just a hair less than 900. I had to crank the idle adjustment screw quite a bit to reach that number. Now I'm beginning to wonder if the culprit perhaps lies there - although that wouldn't explain the rough flubbing / missing that was happening when it was raised to 1,500 or so rpm...

-Wayne

[Wayne 962]

I found this photo from the build of the motor - looks like the proper spacers and gaskets are in there (so not the same problem that John Walker had, although this only shows one side):



-Wayne

[FrankM_]

Wayne,

I would only check for a stable 0,25V from the afm at idle. That is the only thing that matters for your idle condition. And the temp probe ohm range as the ecu uses both values to try to calculate air mass from the flap (volume) and temp probe.

Both should be stable at idle and in range. You can test both from your breakout box, no need to move the flap.


Sent from my iPad using Tapatalk

[Wayne 962]

Originally Posted by FrankM_

Wayne,

I would only check for a stable 0,25V from the afm at idle. That is the only thing that matters for your idle condition. And the temp probe ohm range as the ecu uses both values to try to calculate air mass from the flap (volume) and temp probe.

Both should be stable at idle and in range. You can test both from your breakout box, no need to move the flap.


Sent from my iPad using Tapatalk

Thanks Frank. Both have checked okay.

-Wayne

[Wayne 962]

Originally Posted by Steve W

That said you may have an injector on the bank that is not closing completely, or sputtering on low duty cycles, such as near idle, that will cause that cylinder to idle excessively rich or lean, and if it's on the bank where the O2 sensor is, it will send a signal accordingly to the DME of the average mixture of those three cylinders. This I'm assuming your O2 in your exhaust is only reading either the left for right bank. The LM-1 at the tailpipe shows a different reading, because it's displaying the average of all six cylinders. So this is why I previously suggested if there's a suspect injector, to try swap them side to side and see if the car's O2 sensor displays differently.

Indeed, agree - this would only be a condition that would occur at idle, as previously, the LM-1 in the muffler was reading 14.7 pretty much spot-on. Unless perhaps the LM-1 was picking up ambient air from the outside. Yup, the next test will be to swap the injectors. I will do that now.

Another thought - reading the Bentley manual, I noticed it said that the wire harnesses from the two position sensors and the O2 sensor were "shielded". While I'm not 100% sure that is correct, it got me thinking that the whole big mess of wiring in the engine compartment (routed differently because it's a 914) may be picking up stray signals from the plug wires, etc. (the O2 sensor wire was inadvertently wrapped around one of the plug wires previously). My gut is that this is not the issue, but I'm starting to think way outside of the box now.

-Wayne

[FrankM_]

I doubt that it would be interference because your external wideband sensor confirmed the .88V reading, presumably not using the internal wire harness ?

You are using the original cable harnass with the shielding in place I assume.


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[Wayne 962]

Originally Posted by FrankM_

I doubt that it would be interference because your external wideband sensor confirmed the .88V reading, presumably not using the internal wire harness ?

You are using the original cable harnass with the shielding in place I assume.

It's the original harness as far as I can tell, but it's been slightly modified to work in the 914 (modified by the builder, I have photos of this).

I agree that there shouldn't be interference on the O2 sensor, but my thinking was that there might be dirty signals floating around on perhaps some other lines. Again, starting to grasp at straws.

Taking a break while the spilled gas from the injectors airs out...

-Wayne

[Wayne 962]

Photos of the harness (from the build):




-Wayne

[Wayne 962]

Another straw to grasp at - I've been running it without the K&N air filter on - just open to the air. That should not make any difference either.

It also has these two boots that have been "merged" together to create a 180 degree turn on the air flow (to make it fit in the 914 engine compartment). I did something similar on the Boxster transplant (996 engine -> Boxster) for the Boxster 101 book - worked great! I don't anticipate anything amiss with this (no leaks either), but again, grasping at straws...





-Wayne

[Wayne 962]

A good friend of mine who I've worked with for many years had a BMW of a customer that had similar problems. 1988 535i - they replaced *everything*. The only thing (last thing) they replaced was the fuel pressure damper, and that fixed the issue. I'm not sure if too many people have replaced those on these 3.2 Carreras, but it would seem like it might be something to check out. I do know when they fail, that gas gets sucked up into the throttle body, and I'm not seeing that right now. I disconnected them yesterday and fuel did not spray everywhere, nor was there any fuel coming out of the vacuum hose either.

I removed the injectors and the garage is airing out right now. Something odd though - injector #1 has the paint scratched off of it, and when I pulled the injector rail, the injector stayed in the head, and did not stay with the rail. This means that the clip that attaches the injector to the rail was loose. Gosh, hard to say if this would cause problems like we're seeing, but any little thing that is amiss will be looked at carefully.

I'm headed out now to pick up the plug wires. I will reinstall the injectors (not the wires) when I get back and see if there is any differences.

-Wayne

[brianlay]

I scanned the whole thread and maybe I missed it, but have you watched the O2 signal on the scope throughout the warmup phase?

Also watched the injector pulse width through the warmup phase, to verify that the pulse width becomes noticeably shorter as the engine starts to run badly? This would confirm that it's the ECU causing it to go lean at idle after warmup.