944 Lux Not Starting

[simdel1]

After a very extended break to deal with children/house/work and other grown up stuff, I'm now in the process of trying to recommission my old 944. Unfortunately it now wont start. It's cranking but making no attempt to fire

So far, I have:

• Confirmed that the fuel pump is working, but only when I bridge the DME relay pins
• Tried the DME relay paper-clip trick which meant that it started to fire, but it sounded like it was only trying to fire on 1 cylinder.
• Tested the DME relay as per the Clarks garage tutorial which seemed to suggest that it was working fine. (both relays within the DME relay module seem to operate correctly when power is applied)
• Checked for leaking injectors by removing the rail and injectors and bridging the pump relay pins as described in Clarks garage. No leaks that I can see.

The last time I was working on it, the car was running a bit rough and I suspected injectors, so I have an injector rebuild kit which will be my next job alongside checking for spark.

However, I'm concerned about the DME situation. Everything I've done seems to suggest that the relay is fine, but I have to bypass it to get the engine to try to run. This leads me to suspect the DME controller itself is potentially at fault (I assume the DME provides one of the low-side inputs to the DME relay to activate the pump?). Is there a way I can confirm or eliminate the DME controller from my investigations?

 

[PSH]

Hi Simon

For the next step, I'd check the fusebox contacts, you may find that they are corroded and thus not giving enough power to the DME relay. Try cleaning all of the contacts for all fuses and relays and check that the earth straps around the car are good. Also, how is the battery? might be worth giving it a boost too.

good luck

Pete

 

[simdel1]

Hi Simon,
There are businesses that you can send your DME to who will test it and report, but before you go there - if it's been years without running then I'd start by draining the fuel tank and getting some fresh stuff in. Also check all the engine earth points, especially the two near the back of the engine. The DME won't let the car start unless the cranking speed is high enough, so make sure the battery is giving plenty of spin. Check the distributo cap and rotor arm.
Just some initial thoughts, keep us posted... I'm sure some other folk will have more/better ideas too.

 

[bmnelsc]

The workshop manual Vol 1 engine has the DME test process outlined - actually goes through all components of engine management. Is complex and requires an oscilloscope for some things but probably all the steps around these will eliminate a lot of potential problems if you ultimately need to send your DME off to specialists. Might find its a simple problem.

 

[Waylander]

Just a quick check is to see if the tachometer needle bounces as you crank, the Motronic ECU requires at least 200 rpm before it will switch the fuel pump on, be very careful fiddling with the injectors, new ones are £500 each from Porsche

as suggested above, new fuel, a fully charged battery, clean and good ground connections can only help

 

[simdel1]

Wow, thanks for all the advice guys!

I've got the battery back on charge to see if that helps. I checked the fuse box and it looks quite crusty so I can imagine lots of other things won't be working even if I get it fired up so I'll have to clean that up next. I can imagine that the earth points must be just as bad!

Then, once I've got the injectors bolted down properly again I'll drain the fuel, get some fresh fuel in it, check the tacho speed during cranking and see how much closer I am to getting it running.

I'll avoid touching the injectors until I know for sure that they're not working. I don't fancy forking out £500 for one! I've seen places that do ultrasonic cleaning and servicing of these injectors. Has anyone had any success with those sorts of places before?

I suspect the non-running aspect of this recommissioning is only the start of the journey to getting this back on the road...

 

[Waylander]

Professional cleaning is the only safe way really
Mr Injector is a fair place about £80 all in

 

[simdel1]

I've charged the battery and I've tried to clean up a number of the fuses and earth points in the engine bay. I've also given it some fresh fuel. It seems to be firing a bit better even without any of the DME relay tricks, but it's still not catching. I can see revs on the tacho so I presume the ecu is happy to activate the injectors.

I pulled the spark plugs out. Three are fouled, only one seems to be normal. Is this pointing to spark being the problem? I think I'll try replacing these plugs anyway - they don't look great.

More investigations to come. I'll keep you posted.

 

[Waylander]

Bit uneven in colour, new plugs will certainly help
but one is a bit light might be an air leak

 

[simdel1]

I've just received a bag of fuses so i can replace all of them rather than trying to clean them up.

I've got a new dizzy, rotor arm and set of plugs on order. I'll see if that makes a difference.

 

[simonthomas]

Have you checked you have fuel at the rail? Also checked that you have spark?

 

[Waylander]

No update for nearly 2 weeks, need a update from the OP

 

[scam75]

Maybe it started and he went on a long drive.........................[]

 

[Waylander]

Big fuel tank Stuart