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

[Wayne 962]

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.

That was my initial thought - that is why we had the injectors all cleaned, mini filters replaced (inside the injectors), and completely calibrated and tested. All good now (and didn't fix the problem, unfortunately).

-Wayne

[Wayne 962]

Originally Posted by john walker's workshop

Use an IR temp tool on each exhaust tube. Did you get a CO reading out the tailpipe? HC? The mixture has to burn before you get CO. High HC shows unburned fuel. But you Knew that.

I've got a FLIR camera that's like one of those IR temp tools on steroids. I ran out of time yesterday to look at it - the plan is to do that tonight. The air-fuel mixture ratio is equivalent to the CO reading out of the tailpipe - the LM-1 gives you the exact number so that you don't have to guess at it. Still, I don't have a pure CO or HC meter, as I suppose that would indeed show an unburned (fault) condition.

Tonight's test plan:

- Smoke test the exhaust (as Steve suggested)

- Install new O2 sensor (as everyone suggested)

- Take an IR photo of the exhaust to check for variations (as J Walker suggested). Frankly, I'm slightly disappointed that I haven't already thought to do that - I didn't get the feeling that one or two cylinders in particular were down. The FLIR camera wasn't really cheap (like $500), so I try to use it every chance I get (useful for finding small animals in the backyard at night!).

Thanks, I will keep everyone posted -> heading to the garage to start the smoke test right now.

-Wayne

[mysocal911]

Originally Posted by Wayne 962

- Install new O2 sensor (as everyone suggested)

-Wayne

Don't waste your money on that now, a 911 3.2 engine should run OK (no missing) with the O2 sensor disconnected, although a little rich.

[john walker's workshop]

My feelings exactly.

[Wayne 962]

Monday Update:

Okay, so I did the following:

- Smoke tested the exhaust (as Steve suggested). I found a few small exhaust leaks at the muffler gaskets (tightened those), but none that were significant to make a difference. Nothing came out of the exhaust manifolds that I could see. So, there's probably not an exhaust leak there that would be interfering with the proper operation of the O2 sensor.

- Take an IR photo of the exhaust to check for variations (as J Walker suggested). Unfortunately, the heat exchangers make it nearly impossible to see / tell what is going on. I also can't directly see the exhaust ports either, making it very difficult to take accurate measurements:




- Install new O2 sensor (as everyone suggested). The old one looked fairly new, and I think it only has a few hundred miles on it (despite being 12 years old). I'm not sure if these age over the years without any use (I don't think so), but I figured replacing it anyways would check this off the list. Bottomline - the new sensor made no difference at all (what Dave and JWalker said already). I was hopeful, but I really didn't think the O2 sensor was the problem either. The car acts exactly the same, unplugging it makes it run better (not perfect but better). This is beginning to not make any sense whatsoever.

Here's a video, pretty much the same as yesterday (multimeter and oscilloscope show the O2 sensor, the LM-1 shows the mixture - car runs fine to start up, then terribly, and then I disconnect the O2 sensor and it runs better).



Steve W. wrote that my cylinder head temp resistance values didn't look quite correct. He was / is correct. However, I discovered something odd tonight. The values that I have been measuring have been on the breakout box *with the DME* connected and running. With the DME connected, the values for the sensors are different than when the DME is disconnected. This doesn't seem quite right to me, but I'm not an expert on this. I measured the cylinder head temp sensor this time, using the breakout box, and unplugged from the ECU. These values seem to match closer the values that are shown in the factory manuals:

107 ohm after being run for about 10 min or so
158 ohm after sitting for 3-5 minutes off
170 ohm after sitting for 5-7 minutes off
230 ohm after sitting for 10-15 minutes off
83 ohm after running again, checked oil temp at oil filter, 180 degrees F.
85 ohm after turning off the car, two seconds after
86 ohm after turning off the car, four seconds after
87 ohm after turning off the car, six seconds after

This is testing it with the ECU unplugged. With it plugged in, the value is 4.59 mega-ohm. Odd, but I don't know what's normal.

Ambient air / intake air temp sensor was the same thing:

1.856 ohm @ about 75-85 degrees F.

This seems fairly correct, as per the factory manuals. Again, the values I was recording yesterday were on the breakout box with the DME connected. I guess to get accurate values while the car is running I would have to place an inline diode inbetween the sensor and my multimeter.

At this point, I'm beginning to completely run out of ideas. I've tested nearly everything. I don't have a spare ECU or a spare air flow meter (I really don't think it's the meter based upon the tests that I've done). I'm going to try to borrow an ECU from a local shop, perhaps tomorrow. I suppose there could be an issue with the wire harness, but I don't think so, as I've done all the tests at the breakout box, which should eliminate any harness issues.

Recap: The car runs terribly at idle once the O2 sensor is plugged in - the mixture goes lean. If it's unplugged, then it runs "okay" - not perfect, but "okay". With the O2 sensor plugged in and raising the rpm to about 2000, the mixture is spot on at 14.7, but it's still flubbing again. Car runs perfect on startup - no missing, no nothing. After 1-2 min it starts to run poorly. Note: this period of "running well" in the beginning two minutes is indeed dependent upon engine temperature. If the engine is completely cold, it runs for about two min before flubbing. If the engine is warm, it will only run okay for about 20 seconds or so. So, this "warm-up" period is indeed temperature dependent based upon the temp sensor (presumably the head temp sensor). That would seem to hint at proper operation of the head temp sensor?

I pulled the ECU out of the car. It always amazes me how bad these always look if you're buying a used one. They really look like they've been left outside, etc., and/or kicked around the parking lot a few times. The only ones that I have seen that don't look this way are the spare ones I have for the 959. Those look nice. This one doesn't look mint (but none of them do, especially the ones for sale on the forums / eBay). It doesn't appear like it's been opene up or messed with, but I can't get for sure. If someone did open the case, then they did a very nice / careful job making it look like they didn't open it up. Usually you can see scratch marks all over it, etc.




I'm definitely beginning to run out of ideas. This probably would have been easier to diagnose if it wasn't a transplant into a 914. I.E. - it took me about 45 minutes just to find the test plug that is used to set the idle (hidden and tucked under the batter tray - had to trace back the wire harness, which is not easy to see in the 914 engine bay). I think the next step would be to try to swap out the 3.2 ECU, but I don't have a big pile of them under my desk!

Thoughts?

-Wayne

[proporsche]

Wayne did you try to play with the fuel enrichment setting on the computer ..there is a back side plug and settings 1-7 turns....

Ivan

[Wayne 962]

Originally Posted by proporsche

Wayne did you try to play with the fuel enrichment setting on the computer ..there is a back side plug and settings 1-7 turns....

Ivan

I have this on my list for tomorrow. I think I need to go over all of this again, it all started with a surging idle and now is something much worse. I’m going to go back to basics and reset the idle mixture and the idle speed again tomorrow.

Wayne

[john walker's workshop]

Wouldn't it be weird if it had carb phenolic spacers under the intake runners like that last problem child I had. No slots for injector spray. Found eventually when the injectors were out. You could see the blockage through the injector port. Like if a screwdriver was poked in there it would contact the spacer.
It did the exact same thing when started cold. Ran great for a minute or so, then deteriorated.

[Steve W]

Does your exhaust mount the O2 sensor where it only reads one bank of cylinders? If so you can try swapping the injectors left to right and see if the results differ, either the whole batch, or two cylinders at a time.

[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. And also pull each spark plug connector to find a missing/weak cylinder.

Use a timing light to check each cylinder (around each spark plug wire) by watching the flashing light as the engine is revved for mis-fires.

[Wayne 962]

Originally Posted by john walker's workshop

Wouldn't it be weird if it had carb phenolic spacers under the intake runners like that last problem child I had. No slots for injector spray. Found eventually when the injectors were out. You could see the blockage through the injector port. Like if a screwdriver was poked in there it would contact the spacer.
It did the exact same thing when started cold. Ran great for a minute or so, then deteriorated.

I'm going to mess with the car this afternoon and try some things (more on that in a bit). If I don't make any progress, I will pull off an injector rail and take a look. Good suggestion.

-Wayne

[Wayne 962]

Originally Posted by Steve W

Does your exhaust mount the O2 sensor where it only reads one bank of cylinders? If so you can try swapping the injectors left to right and see if the results differ, either the whole batch, or two cylinders at a time.

Steve - I'm getting very close to opening up the ECU and taking a look inside (and then sending it to you for testing). I think you live like walking distance from my house!

As for the injectors, I pulled all of them a few weeks ago and sent them to RC Fuel Injection for a complete overhaul. So, I'm pretty sure that the injectors are good, I also did check them manually using the breakout box to make sure I heard them clicking on and off when triggered (as per the manual). Here are the results from RC:



-Wayne

[Wayne 962]

Originally Posted by mysocal911

Use a timing light to check each cylinder (around each spark plug wire) by watching the flashing light as the engine is revved for mis-fires.

Yup. Good tip. While I didn't do that with a timing light, I used an inductive sensor (same one used on the timing light), and plugged it into the oscilloscope to check the spark pattern. It looked fairly good to me, which led me to believe that there wasn't an ignition problem. Since the car starts fine and runs fine for the first two minutes, that would indicate that the ignition system is okay. If there were a problem with the wires (the only thing I haven't replaced yet), it would theoretically show up 100% of the time, not just in the warmup stage?

I posted the output of the spark wire inductive sensor (did all cylinders, but this is just one) on page one of this thread, but here it is again:



-Wayne

[Wayne 962]

Okay, so I could not sleep well last night trying to figure out what I missed on this. After taking a step back, I'm now really confused. So, the original problem was surging at idle, which has now gone away. But surging is typically caused by a richer mixture - now it's super lean. So, something has changed, but I didn't really mess with anything - the biggest change was that I had the injectors rebuilt. Four of the injectors were "dripping" as per RC Fuel Injection's report on them - that would / could probably cause a rich condition and surging at idle. So, fixing them would presumably create better performance at operating range, but I suppose might make the mixture go lean at idle. But with the O2 sensor plugged in, the car *should* recognize the lean condition and correct. Hmm...

The car runs somewhat okay with the O2 sensor unplugged, and terrible with it plugged in. The LM-1 air fuel meter shows it running slightly richer with it unplugged, which is expected. When warm, it seems to be running pretty well, but I'm *very* picky and if it misses every once and a while, I'm not happy. With the O2 sensor plugged it, it runs super-lean. Which means that the signal from the O2 sensor is confusing the computer (thinking that it's running rich when it's really not). Since it's a new sensor, it may be a fault in the wiring harness or the circuitry of the ECU. I did remove the breakout box from the system and tried it without the box installed and the problems remained the same.

With all this in mind, I formulated a new test plan for today:

- Check the ground from the hood of the O2 sensor to the chassis. We have stainless steel headers installed, and the ground may not be that good.

- Also check the acutal values coming out of the O2 sensor without the ECU connected. This *should* match the output performance of the LM-1 meter. This is a brand new O2 sensor - so there shouldn't be any issues. The first time that I looked at the O2 sensor, I noticed that the wire was looped around one of the spark plug wires, so I fixed that. These are Magnecor wires by the way - one thing to perhaps think about would as to whether the spark plug wires were interfering electrically with some of the sensor inputs. I don't think so (as I scoped them on the breakout box), but I'm opening my thought process up to anything at this moment in time.

- I'm also going to plug in the O2 sensor that is out of the car, and stuff it into the tailpipe (the other side of the LM-1) and compare the values to the one that is installed in the pipe. I'm not sure if this will work, but again, it's more data. So, at this point, I'll have three O2 sensors being recorded by the oscilloscope so that I can compare them all. I don't expect to see any problems, but I want to check - this will also expose any ground issues.

- Kenny at Autowerkstatt offered to lend me a cylinder head temp sensor to check mine out. He mentioned that several times throughout the years, the sensor has 'tested' okay, but replacement has fixed problems. So, I might drive over there and try that later on today.

- I'm going to open up the DME and take some photos and also check the "fuel quality rating switch" on there to make sure it's in the proper position. (just did that, it was turned completely counter-clockwise, which is the default/correct setting).

- Check the alternator voltage to make sure it's in range while running (did this already, but I will do it again).

- I'll go over the setting of the mixture and idle speed one more time:
Setting base idle and CO mixture
1) Oil temp at 90C
2) All electrical consumers off (AC, heat, lights, ...)
3) O2 sensor unplugged
4) Adjust the CO screw on the AirFlowMeter for CO=0.8 or AFR=14.2 (clockwise=richer)
5) Now connect O2 sensor
6) Bypass idle speed stabilization by bridging B&C terminals on test port (left side near rear fuses)
7) Adjust idle speed with bypass screw on ThrottleBody, 84-85 cars are 800RPM 86-89 are 880RPM, set base idle 20to40RPM above target, if target is 880RPM set base at 900 or so.
8) remove jumper

I grabbed this image from The Samba - shows which way definitively to turn the idle mixture screw (which can be confusing as it's mounted upside down on the 911):

https://www.thesamba.com/vw/forum/viewtopic.php?t=356377




- I don't like to do this, but I will test the intake gaskets by spraying carb cleaner on them. Spraying combustible materials into a hot engine compartment is not one of my favorite things to do (smoke test didn't show any problems, so I don't expect any here).

- I have the build photos from when it was put together, and there is a photo of a replacement harness being spliced together. I there is some ground wire or something taped to the outside of the harness, I will investigate this further. Since this is a transplant, who knows that the heck may be going on. It's quite difficult to figure this out when it's been patched together - it took me about 30-40 minutes just to find the test plug (hidden under the battery tray).

- I'm going to check fuel pressures again while running - I didn't take a photo of the pressures while the engine was running, just when the pump was running while I jumpered it at the DME relay.

-Wayne

[Wayne 962]

Before doing all of that, I took apart the DME. The unit had "85 3.2" written on it in sharpie in the build pictures (faint traces of that can be seen on the cover, so it's the same unit as in the build photos).

- PN 0 261 200 082, 911.618.111.20 - appears to be from a 1987 911.

- Appears to have the correct circuitry for the O2 sensor (as expected)

- EPROM shows a 24-pin socket, which is consistent with a 1987 DME.

- Conformal coating is flaking off in a few spots.

- The soldering around the fuel quality switch looks a bit "different" than the rest of the board.

- There is a slightly black mark in the center part of the board, but it almost looks like it was black ink - not burn marks...

If I can't get this resolved, I think I'll send it off to Steve Wong for inspection, and perhaps a chip put in (perhaps ROW chip that won't use the O2 sensor).

-Wayne

[john walker's workshop]

Loren is right around the corner.

[Wayne 962]

Originally Posted by john walker's workshop

Loren is right around the corner.

Thanks for the suggestion John.

On June 28th, 2012, after about 5-10 warnings, I gave Loren a five-day timeout from the forums. This was based upon his tone in the forum thread "Performance Tuning - The Myth - ". It was a difficult situation for us because he was one of our vendors (rebuilding CD boxes). But the number of complaints had reached a level that resulted in semi-daily emails from forum members in my inbox. I was way more patient with him than with anyone else on the entire forum, in the history of the forum, because his knowledge is / was a tremendous asset.

After that 5-day timeout, Loren never posted again on the forums, and has never returned a single phone call from anyone at Pelican.

I have no ill will towards Loren, and he certainly seemed like a nice guy every time I spoke with him. However, I'm not going to try to chase Loren down when there are other qualified people (Steve W., Ingo, etc., also near by).

-Wayne

[proporsche]

deleted sorry..i was a little harsh....afterall it was 25 years ago....people change;-)

[john walker's workshop]

I deal with Loren for everything electronic. nice guy, never an issue. ymmv I guess.

[mysocal911]

Originally Posted by Wayne 962

- Kenny at Autowerkstatt offered to lend me a cylinder head temp sensor to check mine out. He mentioned that several times throughout the years, the sensor has 'tested' okay, but replacement has fixed problems. So, I might drive over there and try that later on today.
-Wayne

Once the engine is warm, about 3-5 minutes, the temp sensor can be bypassed with a paperclip.
After the temp sensor reaches less than about 300-500 ohms, it has basically no effect on the injector pulse width.