Measuring running voltage to the injectors might be a good idea. I purchased a 3.2L for my 914 project about 2 years ago. The wire harness and electrical connector boots had seen better days so I decided to replace all of the electrical connectors and put a new outer jacket on the harness. When I tore off the old jacket, the two main power feeds for the fuel injectors near the DME relay where the main feed from the relay branches in 5-6 wires had melted insulation and one of the leads only had a few strands of wire still attached. It looked like there had been a short in the system at some point and this area had been a point of high resistance that had overheated. If I had not opened up the jacket, I would have never found this damage. With a few strands still attached, the system might still have functioned but with greatly reduced current capacity.

I completed the install of the motor this past weekend and will try to fire the motor tonight. Wish me luck.

That's a good thought. I just bit the bullet and bought a new one, they are only $10! Sometimes the o-ring is damaged, so this includes the o-ring too...

-Wayne

Okie, I got the low down on these. It seems that these non-resistive plugs appear to be quite difficult to find these days, as they were discontinued about five years ago or so. This is the story:

W7DC - discontinued about five years ago, replaced by W7DC+
W7DC+ - also discontinued several years ago, replaced by W7DC0
w7DC0 - also discontinued several years ago, superseded to the 7900 series plug, which is the WR7DC+ plug, which is the one with the resistor and the only one available from BOSCH right now.

One can try to run a slightly hotter plug, like a W8DC plug (or W8DC+ or W8DC0, which are also all discontinued).

NGK - also doesn't have a replacement plug without a resistor, as far as my sources have indicated.

There is supposedly a Champion plug (don't know the part number) which is supposedly a replacement. These are cheap and available, but I don't have the part number for them. This page *may* help, but there are many resistor plugs included there, so some research would have to be done: https://www.sparkplug-crossreference.com/convert/BOSCH_PN/W7DC

I've been told that if you can hear a buzzing in your radio when you rev the engine, then that most likely means that you have non-resistive plugs and wires in your car. My parts sources implied that the resistors may have been installed to minimize electrical interference in the car's chassis. Not sure about that one, but I thought I would mention it...

-Wayne

Good thought. However, I already swapped out the harness with another one that I borrowed from Steve W. - which made no difference. I thought for sure that was it too!

-Wayne

I have checked quite a few times, and there are indeed some minor electrical bugs on the car (voltmeter in the dash reading low, etc.), but for the most part, the electrical system is fairly solid. Good grounds, nothing too wonky that I haven't fixed already by cleaning contacts with a wire brush (like the cigarette lighter reading 10.5 volts - that got fixed with a wire brush).

-Wayne

Yup, got that checked out multiple times. The spring was a bit weak (the one that pushes the throttle back against the switch), so I replaced both springs.

-Wayne

Yup, a while ago Ingo suggested that I wire the injectors directly up to the battery +12V on that end, instead of running it through the ECU. I did that with some beefy 14 or 16 gauge wire - didn't make a difference. :(

-Wayne

Might as well throw some new injectors at it. Maybe a flaky injector coil? I know they've been cleaned and flow checked but If you've verified voltage and even gone as far as changing the injector harness along with new plugs, different afm, new fuel tank, new CHT, new fuel rail lines, verified fuel pressure solenoid is working properly, changed out DME and a laundry list of other things, it seems the only things left are a bad wire in the main harness that connects to the injector harness or an injector coil failing.

Beyond that, all I can think of is "Damn!"

Hi Wayne,

I think you still owe the yourself and the group a detailed measurement directly across one injector with an o-scope. Do it with the following conditions:

- stone cold (will tell us pulse length increase due to CHT input with engine cold)
- at operating temp with problem present (want to see pulse length)
- at operating temp with problem gone because other bank disconnected.

You might even go as far as adjusting the idle mixture screw in the AFM and confirm this will change the pulse length at idle as designed. Remember, that screw admits unmetered air into the engine that isn't deflecting the barn door. To richen things up close the screw all the way.

Beefing up the +12V supply to the injectors is only one side of the equation. The GND path comes from the DME through the DME wiring harness and that could be problematic, too.

In the end it is important what each injector "sees" and whether there is a discernible difference in what a particular injector sees with the one bank disconnected.

Cheers,
Ingo

Wayne..i have mentioned earlier the spark plugs W4CC which are used for non CAT 3,2 engines ,you cannot get those?If not i can send you some...

Ivan

Kudos to you for banging your head on this for so long, at this point even if you were going to scrap the factory EFI (which I will be doing on my hotrod build) I would have a need to get to the bottom of this as my OCD would not let it go !.

I have been trying to find the specs for the bosch injectors on this engine, but no luck. I believe these are low impedance injectors which would mean they need a lot of current to be driven properly.
In post 121 you measured the resistance, checked the voltage drop and even replaced with a test harness and another DME. But the issue persists when both injector banks are connected.
Have you thought about checking the actual current at each injector ? since you have a scope, you could use something like this:
https://www.picoauto.com/library/automotive-guided-tests/injector-current/#:~:text=Plug%20the%20low%2Damp%20current,wire%20a s%20in%20Figure%201.

I don’t know if you have attempted this yet as I have not read every page..apologies in advance.

Ingo,
If it was a ground path issue related to the harness, wouldn't that tend to be more a constant problem than the intermittent problem he's seeing where sometimes it runs fine and others not?

Nick, yes and no. If (and that is a big IF) the injectors really see something different are not precisely open for the short idle pulses when all six are firing it could be anywhere in the DME harness, the DME connector, etc.

Wayne has test-swapped DME (so let's rule that out), the engine harness (ruled out) and routed alternative +12V to the injectors. However, if there is say a corroded crimp in the DME harness that would do it. Also a faulty injector can stress the current-regulation inside the DME to where the idle pulses are becoming somewhat garbled. A set of careful scope traces across an injector and ideally across the current-sense resistor inside the DME would give clarity if there are losses somewhere.

Remember the entire system receives GND from these ring-lugs at the end of the DME harness that mount to the engine bay GND point. Internally there is a pretty wild crimping in the DME harness with different GND wires when you open it up.

I really don't think we have definite conclusions as to whether the issue is now better than at the onset oft the endeavour. I have see too many emails with "no change" and maybe some of the observed "improvements" are wishful thinking. It's hard to image you had two root causes at the beginning that result in the exact same issue and now one is addressed the other is intermittent.... Orcam's razor says otherwise ;)

Agree. BUT - I was looking at the problem solely at idle, and thinking, "well I'd better fix that before driving the heck out of it - if it runs like crap at idle, it will run worse under load". That assumption is not true however, the car seems to run very well when not at idle. So, the issue isn't better, but the scope of the problem seems to be limited to idle when the engine is not fully warmed up yet?

The number one culprit that would explain all of this would indeed be an air leak on one side of the motor. That would explain running fine when cold, running rough when a bit warmer, and also the intermittent fixing of the problem at hot (it would be sealed, unsealed, and then perhaps sealed again). It would also explain the mixture differences left-to-right. That would also explain the O2 sensor making the car go lean (as it was sensing a richer condition on bank 1-3). Alas, I have not found any air leaks *anywhere*.

???

-Wayne

Last weekend I finished to built a 3.2L 911 Carrera engine into my 914 (same as Wayne). In my case the engine ran fine when cold but started to run erratic after a few minutes (stationary as well as at high rpm). It turned out that the fuel line to the filter was hitting the valve cover and therefore became warm, probably resulting into vapor in the fuel system. After fixing the fuel line with a tire wrap to the chassis of the engine bay the erratic running disappeared.

My apologizes for hijacking this thread with another problem related to this engine and the 914. At full throttle and high rpm (> 4000) my clutch is slipping. It concerns a 901 gearbox with a KEP stage 2 (215mm push) pressure plate. When I had a 3.0L engine in this car I used a KEP stage 2 225mm push pressure plate, but this was way too heavy for normal street usage. Any ideas or suggestions?

air whine / whistle noise
 

The air whine / whistle of your engine at the video from your message at 05-13-2020, 08:53 AM is identic as mine (using K&N cone air filter). So I think the whistle noise is normal.

Wayne,

In summary your problem statement is “poor idle when the engine is warmed up”, right?

There are several things happening when the engine transitions from cold to warm mostly related to mixture:

- fuel absorption and condensation on intake and head parts gradually reduces
- atomization of fuel mist improves
- ability to generate a stable mixture improves
- internal friction reduces
- temperature of everything rises. Interesting observation from ggraf there.

The CHT is accounting for that by gradually reducing the enrichment. It’s enrichment authority is very significant when the engine is stone cold.

Starting here I remember it was suggested several times to play with the mixture at idle and see if that makes it better (fuel pulse duration from DME). Maybe try any of below when the problem occurs:

- gently push the flapper of the AFM a bit more open
- close the AFM idle bypass screw all the way
- hook up a 5k logarithmic potentiometer instead of the CHT

All the time measure the pulse length with your O-Scope. The potentiometer is a bit more work to realize but it makes it very convenient to take data points while observing the O-scope. The fuel pulse is on the order of around 1ms.

A decade switch resistance box is really easy to connect and use for test. Its also very cheap.

Along the same lines of isolating the CHT for any potential contribution to the problem: Would it make sense to mount a CHT sensor on a temporary bracket somewhere on the engine that does not have as huge of a warm-up temp delta as the heads? Would be interesting to see if a more consistent CHT changes the behavior. This way it's not just the sensor that is being tested, but rather what the ECU does with the reading as well.

I believe Wayne replaced the CHT sensor already and excluded this as possible root cause. If he has the old one it's the perfect parts source with it's harness. Simply buy that 5k potentiometer and wire it up to the pigtail of the old CHT. This makes it a simple tool to modify the mixture in a very wide range.

Yup, I replaced the CHT with a brand new one from Porsche. Heading out on vacation tomorrow or so with the family. I've parked the car for now. It runs very good at speed, but not so good at idle when warm (sometimes). I have a new throttle screw, perhaps I will install that before I leave tomorrow.

It surely feels like an idle vacuum leak, but I haven't found squat!

-Wayne

Thanks for the thought - I tested all the fuel pressures, and I've now replaced 100% of the fuel lines - same issue exists...

-Wayne

So, it has been a few weeks; has there been any new tests or progress?

Last I heard it was stolen, again, and Wayne had to file an insurance claim.



Just Joking!!!

Been on vacation in Montana and Idaho, so no progress until I return!

thx,

Wayne

Okay, so I got back on Friday. Installed the new seat belts (what a pain - they didn't fit properly and required seven modifications per side to get in there), and took it for a drive. It didn't magically fix itself by sitting (that rarely works indeed). I also replaced the idle screw (cleaned it out and replaced it with a new one with a new o-ring). That also didn't make a difference.

The car runs very good when driving, but idling, it's still flubbing and missing and all that. Warming up, again, it seems to run fine. When slightly warm (one min), the idle drops and it starts to flub at idle. I just ordered new injectors that are AC DELCO alternatives - Sal gave his somewhat blessing in this thread here: http://forums.pelicanparts.com/porsche-911-technical-forum/327832-alternative-fuel-injectors-17.html They are OEM cross-references to the -364 injectors, so they *should* work okay.

Remember, when I plugged in Steve W.'s borrowed injectors, it ran much different / better, until after a short while, it started running crappy again. Indeed, I thought that this was due to crap in the fuel system (which would have then clogged up Steve's injectors. So, I had mine cleaned again (one came back dead), and then reinstalled them again. Same problem.

So, twice I sent my injectors out, and twice they came back as indicating they had problems, and twice the cleaning did not fix the problem. Steve W. and I think Sal too have both mentioned that sometimes injectors just go bad and no amount of cleaning will help. Not sure, but it's worth another try. Again, I swapped around injectors previously, with no discernible difference.

If the new injectors still do not fix the problem, then I think the only thing left to try is to change the chain tensioners. If one of them is lagging at low rpm, then that could explain the left/right imbalance in the mixtures. Unfortunately, with these very early, primitive engine management systems, there's no way to measure bank-to-bank cam timing and any differences. On the Boxster, you can do this test, and it's quite useful for determining problems with the chain, the tensioners, or even the IMS bearing (sometimes). But alas, there's nothing on the 3.2 motor that will assist you with this. As some of you may recall, I did check the cam timing and it came back within spec (as best I could check it on a 914-6 with the engine still in the car!). I may or may not be able to replace the tensioners with the engine still in the car - the motor mount is welded to the front bulkhead, and may not allow enough clearance for that. It's important to note that I do not hear any major rattling or any other chain tensioner noise, except for what sounds like a "slap" when the car misses.

Anyways, that's the update! Thanks,

Wayne

O2 unplugged permanently? They run better that way. The flubbing after one minute could be the O2 kicking in.

Yes, still unplugged...

-Wayne

Does this motor have a non-stock cam? If so what cam is in it? These motors can tend to idle a bit erratic with non-stock cams, and they need to be in the 13.8 to 14.2 AFR at idle to idle decent, they do not like to idle leaner than 14.4 when warm. Also note that an injector with a spray pattern issue will act up more at idle at very low pulse widths (very short on time). Hopefully those aftermarket injectors you ordered help?

I'm fairly sure it's a stock cam, but I haven't owned the motor since new, so I suppose anything could be. The injectors I ordered are the AC DELCO ones I displayed here:

http://forums.pelicanparts.com/uploa...1589796255.JPG

-Wayne

With more time behind me than ahead I don't screw around with anything that's not cooperating.

Since the car is a GT look it's a natural for a pair of 46mm PMO's. I'm reasonably sure Richard would look out for you.

The best part is the 46's are easy to tune. Fuel and fire and off you go. No electronic EFI BS.

So far, 24 pages of nothing but a headache.

What is your time worth?;)

So... where is your wideband 02 sensor plumbed in at?

... You know, the tool you need to actually see whats going on...
You'll need one even to get a decent tune on Webers without guesswork, because reading sparkplugs does not really work with modern fuels, except (maybe) race gas.

The better units even have a programmable narrowband output to hookup to older factory FI rigs to make them run at the afr you want them to.
.....................
This could be something as simple as a vacuum leak, or grounding or even fun with 30+ year old factory efi wiring harness. A good start would be finding a local shop that can do a smoke test, although there are other ways to test...

I would normally suggest dropping one of the newer efi systems on it... I have been daily driving Megasquirt "junk" for over a decade now, I and a lot of other folks can create solid tune on a normally aspirated car in half an hour given a few freeway onramps and some light throttle cruising/city traffic. The tuning and log analysis software is excellent.

Also, the ability to datalog everything at up to 400hz makes diagnostics a thing.
(MS3 to a fast internal SD card, good subset, you choose what you want to log))

The reason I wont suggest that is you say the car drives fine, and just stumbles at idle... something that NEVER would happen with Webers, because they contain magic fairy dust...
:rolleyes:

Webers do make for great throttle bodies btw... The music a set of independant runner itbs or webers make is almost worth it, and with a good programmable EMS they can be almost as drivable as the EFI setup you have.

One last thought... There are folks that make super quality replacement efi wiring harnesses for older cars... If it turns out to be a wiring issue thats really widespread, that might be an option, although you could likely go with a ms3pro setup at that price.

If its just a connector reliability issue, the USAF figured out how to (usually) prevent aircraft from falling out of the sky long ago... https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKE wi1_uC7nvDqAhUKTKwKHUVpB-YQFjAKegQIARAB&url=https%3A%2F%2Fwww.corrosion-protect.com%2Fwp-content%2Fuploads%2F2018%2F07%2FScott_Dobson.pdf&u sg=AOvVaw3-OXqiWs5rJpsAQyiNa1Zk

The Navy stuff works just as well for ~$12 a can, vs $80 for the supercorr-A the USAF and aircraft manufacturers prefer.

Carbs are a pain too. I have a set of 46s on the 2.8RSR rally car that are all gummed up with crappy California fuel. That is the next car to make it into the garage! :)

-Wayne

In the previous pages, I documented how I went through and have performed multiple smoke tests, checked the harnesses, etc. There aren't too many things to go over on this. Injectors and perhaps a chain tensioner are the only thing that I can think of (and pretty much everyone else I've talked with). This one is a strange one...

-Wayne

I still suggest getting a wideband 02 unit... otherwise you are still troubleshooting in a cave with a dead flashlight...

14point7.com has a somewhat pricey but excellent unit with extensive datalogging ability for afr. ignition and a few additional sensors. Comes with the logging software.

I suggest reading this thread before you post.

Thanks for the suggestion, which is good. Indeed, since day one I have had the LM-1 wide band monitor plugged into the car and have been recording all of the values.

-Wayne

Great, so when the idle starts "flubbing" at 1 minute, what happens to the afr?
Any ability log ignition timing as well?

I forgot about this thread ages ago, I'll go back and read 475 posts, maybe tomorrow.

It's detailed in the previous threads. There is a mismatch between left and right AFR - one lean and one normal / rich. This has been the crux of the confusion...

-Wayne

ok, caught up a bit through the first month... Think I confused this for a long ago efi thread.
You have a ton of good help here, so I'm going to suggest a couple more ideas and check back in in a month...

Have you tried installing the lm2 and using its fake narrowband output to feed the ecus 02 input?
it will then regulate "stoich" to 12.5:1 or whatever value you desire. This would likely largely fix a good part of your drivability issues.

Your basic problem is essentially what the fake nb output is designed to fix, although you would be actually working around the actual issue... one analog that comes to mind is adding series resistance "ballast resistor" to the cht circuit on djet to drive it a bit richer.

The side to side delta is weird, and could very well be cam timing, but sensor placement and temp matter a lot, The top end 14point7.com wideband controllers can read back/log sensor temperature... They all read back the temp (thats how they control the heaters) but Alans units actually have that info logable, depending on the model.