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The relay in the video is a simple single stage relay. The Bosch Motronic DME relay has two relays inside the package and bench testing is a little more involved than what is shown in the video.

However as Sal stated we are much further along in this case. If all the information given by the OP is correct he has spark but no fuel pulses when cranking. So sensors and relay work fine.The possible causes are

- damaged DME (fuel driver)
- no power to harness for injectors
- shorted injector(s)

As next steps:
- check permanent +12V on injector harness
- check continuity from 35 pin DME connector to injector plug
- check for fuel plus with NOID light and all injectors disconnected

This will ID the faulty component(s)

Ingo

Thank you Patz I found that a while back, but as we know if you have spark those two sensors are good. Why does the noid have to be the LED kind? I got one from amazon that I listed a few posts backs and it's not LED, I'll have to figure out if it works anyway.

So there's been a sort of success, the NOID light didn't light up so I assumed I wasn't getting injector pulses, I checked the injector harness up against the firewall (the 4 pin one at the front or non-fan side of the motor) and sure enough it was unplugged, trying to plug it back in was a bit of a stretch so I'm thinking when the engine was out something got mis-routed and put a little stress on it. I plugged that back in and he started right up!

However not all is rosey, keep in mind he was running just fine prior to this falling off, so it's doubtful something failed, more likely I caused an alternative issue. First the idle was super rough and surged a lot as I pulled out of the garage, so I stopped and looked around, found the CHT sensor disconnected, plugged that back in and it settle right down. So I started driving. It quit again less than a mile from the house I got it started finally by giving it some throttle, and it ran okay below 2500 or so RPM but as soon as I put a foot in it, it just falls flat and then wants to stall out.

I checked the flywheel sensors and CHT wire again, I checked the injector plug to make sure it was seated well (Can this plug be installed backwards? I thought not as it has a plastic pin in it). So any ideas on what else, I also checked the obvious plugs near the front (ISV, airbox etc...) could I have damaged the plugs with all the cranking where I had spark but no fuel when I was trying to figure this out?

You don't. A simple 12 volt incandescent bulb will work!

Very unlikely.

Mostly likely you no longer have an electrical problem but possibly an air leak (the AFM
boot loose), low fuel pressure, etc. Check all hoses and connections in the engine
compartment and check the fuel pressure with a gauge.

Good thoughts for sure, but I think I'll start with connectors, the only thing I undid from when it ran perfectly was a fuel rail connection to check for fuel, I'm assuming the injectors not running can't damage the pump as it has as return circuit. So when I get home tonight it'll be a methodical check through all the connectors on the engine. :( I'm also going to check the CHT connector again and see if that got damaged.

You indicated before that the CHT was not connected when you first got the engine
to run after finding the injector harness not connected and the engine ran better
once the CHT was connected, so most likely it's O.K. You can very easily bypass the
CHT using a paperclip when the engine is warm, i.e. bypassing with a cold engine
results in hard starting and possible backfiring.

You can use the NOID light once the engine is running to see that the fuel injected
is increasing by seeing how the NOID brightness increases with RPM. Just pull one
injector connector and connect the NOID light.

Don't assume that some system elements are O.K. now because they were O.K.
before your problems began, i.e. remember you found the injector harness not
fully connected as being your "no injection" problem after doing engine work.

Great thoughts will do that. on the last one, yes but after the engine work I did two full track days and drove the car for at least 6 other hours on the road and It was fine. And prior to it quitting on me on the road it was running great, I really feel like if I had figured out the injection harness right away and plugged it back in everything would be fine, but I could be wrong...

Sorry if someone has mentioned this before but in my case the reference sensor would test fine and then later fail until it failed enough times for me to catch it. Drove me nuts putting it back in thinking it was fine.

Had one of the sensors replaced last year, but I'll double check that. I went over all the connectors tonight and found only one sort of odd thing. There was washer on top of the coil on the black wire, side, but I couldn't find anything else that looked like it should be there, are there two separate wires meant to be on one side of the coil? I did check the CHT and it OHMd out at 1.7K.

Both rails of fuel injection showed lights with the NOID light. Reving it got brighter and flashed at a higher rate, and there's no way to plug the injector harness in backwards. I haven't yet pulled the plugs to see if one or more has been damaged.

OK, so you do have spark and coil pulses? If that's the case and it won't start then you need to check fuel pressure and delivery rate of fuel. Start with pressure first, just force the FP on and you need to have about 36PSI at the rail with pump on engine off. Check this next.

Just to be clear with everyone the thread has evolved, the car starts now, the issue I had the first time (the start of the thread) was a flywheel sensor. The second time we had spark and no fuel injection pulses turned out to be a disconnected fuel injection harness. Now I found that it starts but runs poorly. Idles fine, but when you get on the gas in completely falls flat around 3K and up bogs down like its stalling. IT ran awesome before it quit two weeks ago, the failure of whih was the injection harness. I'm pretty sure that first I need to find something that I might have done in diagnosing the other failures which caused it to run poorly.

Because of this we know it's not the DME Relay.

subscribed ..... anxious to see what this turns up :)

Could be fuel, could be sensor, could be anything

1. Check the intake boot from the AFM to the plenum and make sure it's fully
connected. Any air leak there will cause the AFM flapper to not properly enrich
the fuel as the throttle is opened causing the engine to bog.

2. Check the fuel pressure. You can easily determine if it's a fuel problem when it
bogs by just momentarily disconnecting the CHT and seeing if the bog is eliminated.

3. There may be a problem in the DME control unit not allowing proper fuel enrichment
when the throttle is opened. The control unit needs to be tested in another car to
eliminate it as a problem source.

Rough running, possible vacuum leak? The back side of the Carrera intake has several vacuum ports for brake assist, etc. Are yours hooked up or capped off? During the engine work or driving could one of them become dislodged?

-Jeff

Has anyone mentioned fuel delivery rate. Porsche WSM specifies a pressure test to ensure the regular works and a delivery rate spec. I would test both. Maybe clogged filter.

Agree with others, next step check fuel pressure and delivery rates.

Tell me more about how I do this? Warm it up and then disconnect? What would it tell me about the fuel pressure by disconnecting the CHT? I measure the sensor last night and it seemed within spec.

The vacuum ports on the back are worth looking at I could've knocked something out when I was crawling around back there, gotta get an inspection mirror and crawl around a bit checking for that.

Today I did only one small thing on the car as I'm too annoyed about it right now to really try, and a bit busy. I did print out the page on checking connections for the DME and I'll do that as well in the next day or so.

The one thing I did today was finally identify the wire which should be controlling the fuel pump, at the moment it's wired to come on when the ignition is on, always been that way but I found the wire now, and I have a relay to put it through so eventually I'll make that and the headlight relay change happen. For now I'd like it to run though :)

I think this is what he meant.

When it bogs down at 3000 RPM with the engine warm disconnect the Temperature sensor and short it with a paper clip (or wire) and see if it still bogs down. The short will force it into its warmed up running temperature fuel map.

Actually, no paper clip is used. Disconnecting the CHT momentarily will cause the control
unit to enter the full fuel enrichment mode overcoming the bogging, if it's a lack of fuel
enrichment causing the bogging. Normally when this is done with a warm engine,
the engine will increase RPMs and begin to make black smoke (an overly rich condition).
This condition usually occurs when the CHT fails 'open' on a good running engine.

Doing this test should help to determine if the problem is fuel related. A further test requires
an actual checking/monitoring of the fuel pressure when the bogging occurs.

When it bogs at 3000RPMs does it do this with car parked and in neutral, while you simply free run it up to 3000RPMs? Or does it bog under load while driving? This is important for us to know because if it bogs parked at 3000RPMs it's likely not a fueling issue because a free running (no load) motor at 3000RPMs consumes about the same amount of fuel as a engine at idle. The injection pulse width actually drops significantly (about 3 times smaller) than free running at 1000RPMs.

I'm pretty sure it's only when actually pulling load, it seems to be just fine sitting on the ground, which is going to make it fun to diagnose since it's raining for the next while here.

Since it only happens under load you could be fuel starved or ignition system is weak. Have you looked at the engine bay at night? You may see ignition arcing around the wires at night.

If he wanted to do that fuel delivery test found in the manual where would he source that fitting? Is it the same as the pressure test port?

It wants you to remove the fuel return hose back by the speed and ref sensor plugs (not forgetting to counterhold;)), hook a hose up (fitting required) and jumper the fuel pump. You should see .85 liters in 30 seconds.

Is that point after the regulator and this is the volume you can supply at 2.5 bar?

You are correct, you want to disconnect the return line at the FP Regulator front of the LHS fuel rail, you simply want all return fuel going into a catch can instead of the fuel tank. This after the regulator, so it's going through the regulator. And you simply start the pump up for 30 seconds and you need to have no less than .85 liters of fuel in the catch can.

You don't need the exact matching fitting you just need a hose that fits very snug over the fitting and won't leak. You can even clamp the hose to the fitting if need be. You won't have any significant fuel pressure at that return port or in the hose during this test.

The fuel pressure test is done at LHS rear of the fuel rail near the Distributor while the delivery rate is done at the return hose at the FP Regulator, they are not the same port.

finally had time to do somethings last night, I don't have a motronic breakout box so I was only able to test some of the 30 pin connector electrically, I did that, things seemed good. We checked the coil 0.7 ohm and 5200 ohms I think that's good, but found in my manual it says the values are in "Table 2" but table 2 is no where to be found.

Also popped in a different computer loaned to me by the fabulous folks at Chris's German and started the car. Then we took it out around the neighborhood and it seems just fine. well damn it! we didn't change anything apart from re-securing every connector and those tests. I'm going to have to wait until the weekend when I'll have time to drive it and try the original computer as well.

Your DME likely has solder joint issues. I see a lot of DMEs with intermittent issues these days, I've been fixing a lot of bad joints lately as well as Land lines that are worn through. PM me if you need help with the DME.

I think you just found the issue, it's the DME.

The coil ohms spec is:
Primary winding - 0.4 - 0.6 ohms
Secondary - 5000 - 7200 ohms

That's right out of the DME Master Test Plan

Your coil seems fine, you are in the general area on the resistance and some meters are not that accurate at the very low ohms reading below 1 ohm. So if the meter is not a fluke or hi-end meter I don't trust the readings below 1 ohm.

Not necessarily:

1. The original fuel injection computer needs to be put back in and re-tested.

2. If the computer is bad, it may not be an intermittent connection problem but
a faulty component in the computer.

"Land lines" - You maybe mean circuit traces.

If it's a bad computer, Pelican Parts provides a rebuilding service for that:

http://www.pelicanparts.com/cgi-bin/ksearch/pel_search_2014.cgi?SUPERCAT_FLAG=Y&make=POR&Conte xt_make=&please_wait=N&LastVisited_input=911M&Prev ious_Section=&forumid=8&threadid=823096&command=DW search&description=DME&I1.x=0&I1.y=0

Dave,

Sure it could be a bad dirty contact or a bad component. But I see a lot of DMEs that are failed at the ignition circuit. It may be worth while to have the DME checked out.

I also am starting to see some DMEs with 'circuit traces' literally rubbed off the board from vibration. This I had not seen in prior years but now I'm starting to see this type of failure as well.

I agree with you that he should put the DME back in for another test but having that DME inspected would be prudent at this time, given that a donor DME worked just fine.

Meter is a Fluke so it's likely quite accurate. I'm going to go for a test drive with the new computer, and then swap the old one in and drive more. I've got it out in front of the seat so I Can change it in seconds.

Last night I took the car out for a slightly longer driver, only 3 miles or so but through the subdivision and out on the main road up to 60 and then back in, and it ran very strongly. Then I my computer back in it and took it out again, and it worked fine again! Last time I didn’t get even as far out of my house as I did both times last night before it was clearly broken. I even thumped on the box (it’s sitting in front of the seat at the moment) and nothing changed. So I’ve got three theories:

1. There was a loose connector somewhere and when I went over the engine compartment and checked everything I fixed that
2. Fuel, either the fuel pump is starting to fail and is now working okay again but will shortly fail again, or when we cracked the fitting at the end of the fuel rail we got an air bubble in that took a few runnings to clean up. My buddy Nate who spent time between high school and college as a Ford Mechanic said he had a Toyota that failed like this once.
3. When I originally forgot to put the CHT Sensor on (it was disconnected when I first started the car last Saturday) the DME learned something wrong, and by disconnecting the power (i.e. pulling the DME out) this got reset. Does this happen?

3) is impossible. The 3.2 DME doesn't learn anything. Every time you shut the car off it's a full reset. It also doesn't adapt during driving other than the O2 sensor driven mixture adjustment.

Ingo

I've fixed a few DMEs behaving exactly like you describe. Working great most of the time but then with no apparent reason they act up. These DMEs had bad solder joints. What happens is that the joints are cracked and sometimes they make contact but then as temps change inside the DME they erratically act up. It's prudent at this point to get the DME inspected, when I find a bad joint or 2 I can even photograph them and show the customer. You decide but I highly recommend getting that DME checked out.

I just fixed one last week with exactly same issue as yours. Customer complained to the shop that car runs like crap from time to time, it runs so bad they need to pull over but every time it goes to the shop they can't reproduce the issue. Shop owner finally sent the DME to me and sure enough it had 3 cracked joints. It's back in car no complaints so far.

Since now it's working fine I say just drive it but if the problem comes up again you need to get the DME inspected.

You generally can't visually find problematic solder joints which then requires that
the complete circuit board be re-soldered. Some joints may look good but be bad and
vice versa. Without fully verifying that the computer is bad, i.e. using another computer,
rebuilding that computer is a waste of money.

Most likely the problem/problems:

Dave,

I respectfully disagree, I locate bad joints all the time via my inspection process, I've fixed many 911 and 944 DMEs by inspection alone.

But if it's running now without issue then just leave as id. However, if the problem just pops up again then the DME needs to be look at by someone who has experience in fixing these.

Obviously this method can't find all the bad solder joints and is a very poor way to
properly rebuild, i.e. if that's what being claimed or advertised, any electronic device that may be intermittent.

Dave,

The boards have common places where cracks develop and if you repair DMEs often you know the locations. The reason the 911 DME is so prone to the problem is simply because it's mounted parallel to the ground plain meaning it's horizontal to the horizon. Very bad mounting, in aviation industry this is a huge NO NO practice. Then the DME is also directly bolted to the floor board and what happens is that with years of rough service the heavy components literally drive them self through the board, the pins keep pushing down into the board till they crack. Knowing this is the issue you can easily inspect the appropriate component areas and find the cracks. Here's a perfect example of a DME I fixed and you can clearly see the cracks in the hi-res picture. This DME was DOA and after just fixing those 3 solder joints the DME worked. My point is you can easily find the problems using good inspection process.
http://forums.pelicanparts.com/porsche-911-technical-forum/652375-dme-bad-solder-joint-repair.html
I see DMEs come in like this often, it's very obvious what's wrong, why would you disagree with visual inspection as a decent way to find issues? I'm not saying it's the only way but to say it does not work seems wrong.

And by the way I never claim I rebuild, I repair DMEs. To claim 'rebuild' implies refreshing components to prevent failure and I'm not sure anyone does this? I simply try to make broken DMEs work again and questionable DMEs are tested and visual inspected.

Good DIY (Do It Yourself) info which should save those with a 911 3.2 computer repair
charges. Based on the image of the circuit board, anyone with a screwdriver and
a soldering iron should be able to fix their computer in about 10-15 minutes if they
have a no-spark/intermittent spark condition.

Maybe not but if they have a soldering iron they have some basic interest in electronics. If you saw an obvious fault you would be pretty dumb to ignore it.

How does the flat rate rebuilt board differ from the board that is just troubleshot and repaired. Do you replace all the electrolytic capacitors? Replace all the low mean time between failure parts?

Rick,

I'm done with Dave, the guy loves to argue.

I repair plenty of these DMEs, most repair shops are robbing folks blind! These boards are failing mostly for cracked joints like the one I showed. Burned circuit lines, also very easy to spot, from shorted components. And once in a while I find a bad transistor. This is not guess work, it's what I see from the 50 or more DMEs I've fixed or converted over the years. I may not have a full blown repair shop but I know what the most common failures are and 50% of the repairs are simple easy to see cracked joints. Almost all issues are on the analog board.

If you feel better about the repair because it costs more so be it.

I'm sure that most shops just fix what's broken, no preventive parts replacing is taking place. It's also silly to re-solder an entire board, you need to simply understand the reason the joints fail and you quickly realize what needs attention. I have yet to find a failed solder joint on the digital board of any repair I've done. Why is that? I already explained this, but guys like Dave don't care to listen. The failures are from stress fatigue in the very heavy components.

I have years of experience in Plant Floor Control system that see very harsh environments, we saw failures like this in months. This problem in our DMEs is simply from 30 years of minor vibrations compared to some industrial equipment.

Also don't trivialize how hard it is to spot a failed solder joint visually, it's not that easy unless you know what you are looking for. Also most folks don't have the proper skills or tools to fix the joints correctly. I've seen real hack jobs where folks tried to solder boards, you really should let a pro fix these, I don't think it's a DIY project for most folks.

I am reading these threads because I am trouble shooting a DME problem and thought I would add my 2 cents worth to this thread...



I appreciate the input that people like scarceller bring to this forum and this thread has been helpful and informative for me. Anyone that is servicing many examples of these (be it the DME or any other part of our cars) can see trends and understand what age & time can do to these parts.

What he says about the durability and failure mode of the DME make sense and certainly the approach of fixing what's broke and not fixing what ain't broke makes sense to me and many other DIYers.

I don't understand the arguments sometime brought into such discourse like that in this thread. The approach that scarcellor uses may not be what everyone in this forum thinks best but if it isn't your cup of tea, it doesn't mean it isn't what others would choose.

So +1 scarceller -1 Dave