I'm not ignoring your advice at all. In fact I'm following it. Just not doing It myself for logistical reasons. My plan is to have Protosport follow your instructions. They are best suited for each step - as the car needs other work too. Shift cup and emergency brake shoes. I don't feel comfortable with the current INDY. I didn't bring the car there for a no start issue. I fully appreciate your help and knowledge. I'm not replacing the DME without verification that it's at fault first. I only assumed that in the end that's what the likely problem will be.

 

Originally Posted by sweet928
1. So jumping the DME relay is a better indicator than trying the new relay I gave them?

yes it is because you are testing the fuel injection control system so fitting the 3x wire bypass is a diagnostic as well as a way to bypass all the live feeds, grounds, relays , sensors and ECU control to get your engine started .

2. Is the ECM is the same thing as the DME (computer). The silver metal box.

Yes ....Read the text . ECU ( Engine Control Unit sometimes listed as DME which is confusing )
It is extremely unlikely that there is anything wrong with your ECU unit , leave it alone.
Don't listen to random guesses from others. Do the diagnostic checks I suggested . I am completely familiar with the Motronic Bosch fuel injection and engine management system

3. Seems I can get a "new" DME with a 5 year warranty from DME doctors.(see above ) However I thought tach bounce was a indicator that my DME was ok. I do have tach bounce.

tach bounce has nothing to do with the ECU whatsoever !. The crank position and speed sensor/s are magnets which create a voltage when the engine turns. That voltage is read by the ECU and enables it to control your spark and fuel delivery.

4. Based on your help here, I think I should have it towed to Protosport. They will likely have spare parts to help troubleshoot with there.


Sorry, I missed this (very specific) post somehow (Using smart phone). I didn't realize the DME jump would bypass everything and get me running. After reading this - I am going to take a run over to the INDY today and see if I can get my car started myself. (They are closed but the car is out front). My only concern was that seems they ran the battery down trying to start her because when I tried to start it myself Friday it seemed run down.

Will jumping the car with jumper cables be OK -- while also jumping the DME relay? I believe I've read that jumping the relay will keep the fuel pumps running so I should remove the jump immediately when shutting down the car, right?

Lastly, If jumping the relay gets the car started -- what do you suggest as my next step? I presume you mean just drive it over to Protosport instead of towing. Or are there other tests you suggest I can do with no tools or even a multimeter?

 

So I swung by the (closed) INDY shop and pulled the relay (It was the new one - they must have installed Saturday). I stripped a wire and carefully ran it around the prongs exactly as the Clarks Garage example for the paper clip method and heard the fuel pumps running. I jumped the battery to my wife's VW and got a strong crank but no start.

 

I think that confirms that the problem is the DME. One way to get further confirmation would be to see if the fuel pump runs when the key is in the running position (in other words, turn the car on but don't crank it, then go under the back of the car and feel/listen if the fuel pump is running. If it is, then the DME relay is doing its job.

 

I definitely heard the fuel pumps.

 

no it doesn't confirm the ECU is at fault at all !?

The poster hasn't even checked if there was a spark and fuel to the plugs . There may have been fuel a spark but no compression due to a busted cam belt or the plugs may have been wet or any one of a dozen other problems preventing firing.

The fuel pump doesn't run with the igntion on, in these cars.

It is one of the safety features of the Bosch jetronic and Motronic fuel and engine management systems which prevents the fuel pump running unless the ECU registers that the engine is cranking at 225+Rpm.

I know that you are trying to help but your lack of understanding and incorrect statements are actually causing confusion to both this PO and to future readers.

 

good!

now you see the advantage of following a proper diagnostic sequence of checking.
You have now confirmed the following to everyone.

1. there is 12v+ on the ignition switch.
2 there is 12v+ on terminal 30 of the DME relay
3. that the fuel pump fuse is ok
4. the fuel pump is grounded and working.
5. the ground to terminal 85 on the DME relay is good.

I know also that the ECU has been given a 12v+ supply (via the 3x wire bypass)
I know that the various sensors probably have a 5v+ supply from the ECU

The vital information that I do not know is the following.

1. how much fuel in the tank. ? what age the fuel is ?
2. was the engine cranking at 225 rpm + ?
3. was there fuel on the spark plugs ?
4. was there a spark to the spark plugs whilst cranking ?
5. what the fuel pressure is
6. whether or not there is compression
7 when the engine last ran

 

1. Most of the fuel is new (tank is three quarters full) but I'm not sure how old some of the fuel was as I just bought the car. I don't think more than a few months old though as it was a daily driver.
2. I'm not sure how to verify other than it felt like a strong crank.
3. Can't confirm.
4.'im told by the shop there is no spark. I assume they checked at the plugs.
5. I'll have to ask the shop.
6 same as above
7 engine last ran Monday. Also was running fine for the few days I had her except the no start and tow to my house Sunday. I did get her to start Monday by tapping the relay. Drove her for a bit to charge the battery and she ran fine. No sputtering or stammering or unusual power delivery. Drove her straight to the current Indy with the assumption I just needed a new dme relay.

 

Here is a picture of the engine bay in case that helps somehow. Ie that there is a cold air intake. FYI, the sensor connection in the back of the engine look newer and the FPR does not.

 

ok thanks for the answers.

its important to have at least 3-4 gallons of fuel in the tank when the car has a no-start issue. The weight or 'head' of fuel can help the pump to build sufficient pressure when the pump is old or inefficient.

If your fuel has sat for a few months any water in the fuel will seperate out and can be an issue in starting. Sometimes its necessary to drain the fuel and refill the tank but I'd hold on that for now as the car ran recently

To assess the engine cranking speed you could count how many times the engine turns over in say 15 seconds and multiply that by 4x to get RPM (revs per minute ) If its slower than that you are wasting your time trying to start because the ECU will prevent spark and fuel delivery.

I suspect that the problem is nothing more than a flat battery and the engine not turning over quickly enough.Next time you try to start the car squirt some 'easy start' into the air filter whilst cranking and make sure that you use jump leads to another vehicle and the engine is running at at least 1500rpm when you try to start.

The shop didn't test the spark with the 3x wire bypass fitted y ! With the bypass fitted you need to check spark again. Thats the whole point of fitting it.
The bypass, bypasses safety features built into the system and forces the ECU to generate ignition pulses and injector pulses despite existing faults.

Did you or the garage check the spark with a 3xwire bypass fitted ?
Did they check the cranking speed of the engine ?
It would be very helpful to get some feedback to my suggestions

I don't mean to be critical but it is clear that you have a very limited understanding of how your car works . My suggestion to you would be to find someone you trust that has a good technical knowledge and experience to check the car over . If you don't know anyone then get a qualified technician to come out to the car , there are lots of mechanics that work out of a van and do home visits.

Get the car towed home and do some basic checks or get it towed to a garage that has a qualified Bosch technician.

just a thought . Does the car have an alarm or immobiliser fitted ?

 

He said there is no spark, but if the fuel pump is running, then the car has fuel (if fuel isn't getting to the cylinder, that usually means the injectors aren't being triggered by the DME). Based on my experience with 924S's (I have owned one for 7 years), and in particular, experience with common electronic gremlins on these cars, I think that the poster is describing a problem with the DME.

He said that the car ran fine a few days before and has no spark now, so I doubt that it is a problem with the compression. If the timing belt had snapped, the engine wouldn't crank normally. If the plugs were wet, I assume the OP would have noticed that when he checked for spark. Lots of things could cause a car to not run, but based on what the OP said, it sounds to me like the DME is dead.

Have I looked at the car myself? No. Am I 110% sure? No. I wouldn't rush out to buy a new DME based on my post, but if you can find a known-good spare to try swapping in, I think that would be a valuable (and pretty easy) test to do.

That being said, I had a similar problem in my 924S last summer. I read Clark's Garage pretty thoroughly, and my mechanic (Porsche specialist, veteran of the business, etc etc etc) walked me through debugging it. One of the steps he told me to do was definitely checking to see if the fuel pump was on while the key was in the "run" spot (it was, in my case). I believe that the pump does that to prime the fuel rail so that it has the right fuel pressure when cranking. If you have a reference from Bosch stating otherwise, I will admit when I'm wrong, but you don't need to start calling names or anything.

 

there are so many errors in your post that I just wouldn't know where to begin correcting them so I won't I'm afraid , it will simply confuse the issue further and take this thread off topic.


if you are genuinely interested in how your car functions I would recommend that you obtain a copy of the Bosch fuel injection & Engine management by Charles O Probst .Its expensive but a very worthwhile investment and gives a clear and precise explanation about how the system functions with a trouble-shooting section on all types.

 

Been too busy to move the car. Traveling alot lately. Letting the Indy troubleshoot a little. They have not pushed the car inside yet. Just checking more outside. ..They said no fuel and no spark. They suspect ref sensors first and DME second. They know to fully charge the battery when they push it inside tomorrow to diagnose further. They are fixing the shift cup at the same time. Any thoughts.

 

yes ....take the car to a garage where they have properly qualified technicians who know what they are doing.

It is likely to cost you a shed load of money while your indy thrashes around in the dark buying new part after new part to bolt onto your car in the vain hopes it will suddenly start!

You and your indy are just guessing and not applying a proper sequential troubleshoot because neither of you know what you are doing. Sorry but there it is and it is very frustrating for those trying to help you.


Read the whole thread again Think about the situation and make a note of the important bits .Your car was starting and running fine just a week ago so its unlikely to be any major part failing.

Its extremely unlikely to be your ECU unless rainwater has got into it. They work fine in millions of other Porsches for over 20 years without problem. Unless you have put the battery on the wrong way round or had some welding done on the car it is highly unlikely to be the ECU.
I would concentrate on the more likely causes first.

If your tach needle bounces slightly then the crank position sensor( CPS )is likely to be perfectly good.

Your battery must be fully charged and the engine must turn over at least 200 rpm or it will not start.

look I'm just repeating myself here and you are obviously not listening. I'm wasting my precious time . I have helped people get their cars starting and running all over the World in the past 10 years without ever seeing their cars but it relies on the owners co-operating and giving me feedback.

I'm happy to talk to your indy or a qualified technician or someone with some basic Porsche experience .

 

I'm sorry to frustrate you. I followed your instructions and jumping the relay under jump start didn't work. I'm not sure what the next diagnosis should be. Believe me no one is buying any parts. I am trying to be fair to the indy as I left him with a non runner outside which will need to be pushed out into a busy road to get into the shop. I can't arrange a tow unless i'm there and I cant be there if I'm on the other side of the country. I'm letting him do the shift cup and a few hours of diagnostics with a multi meter. No parts are being ordered. I world really appreciate your help and like to take you up on your offer. Please PM me your contact details and availability so I can arrange to have your talk with my INDY.