Porsche 911 ecu question

[david-j-w]

Dear ALL, I am new to this forum but have been browsing it for years! Great information on here and very knowledgeable posters so I thought I would pose this question.

I have a Porsche 911 Targa 1985 3.2 - has ECU 0261200051

I also have a Porsche 911 Coupe LHD 1986 3.2 - has ECU 0261200052

The Targa I cannot get started, done the normal troubleshooting stuff, new DME relay, new plugs, new Fuel Pump, Fuel Filter, air filter, checked fuses. Car turns over and sparks and tries to start, getting fuel through.

My question is when I start the Coupe there is no buzz on the fuel pump and that car starts no problem.

When I try to start the Targa I get a proper buzz like I would expect and that car will not start.

So can I just put the Coupe ECU in the Targa without causing any issues?

[Chuck.H]

The 84-89 DME computers only run the fuel pump when the engine is cranking. They will however, run the Idle air valve when the key is turned to the on position, you may want to check that - you can feel it buzzing. That will at least tell you the DME is receiving power.

If it was me, I'd swap the suspected bad DME into the car that starts and try that. If it is the DME, search for cracked solder joints, that' s a common problem with these older DME's.

Chuck.H
'89 TurboLookTarga, 378k miles

[pete3799]

Go the other way......put the targa one into the coupe.....if the coupe doesn't start you found the problem.

[david-j-w]

Thanks Guys,

Would you happen to know if these two ECU's are compatible as there is one digit out at the end of the numbers.

I have just tried the working ECU in the Targa and it doesn't start, so same problem.

I will try the non-working one in the working car as suggested.

Cheers

[david-j-w]

Thanks Guys,

Would you happen to know if these two ECU's are compatible with each other? There is one digit different at the end.

I just tried the working one in the Targa but doesn't start either.

I will try and put the non-working one in the working car.

Cheers

[group911@aol.co]

Either car will run with either computer assuming the computers are good.

[david-j-w]

Update.

I fitted the Targa ECU into the Coupe and it started straight away so at least I know that the ECU is good and working. But back to square one on starting the Targa car. The car had been standing a while so does anyone have any helpful ideas that they can think of that may help?

I was thinking that changing the reference sensor might do it but I am guessing I will need to take it to the Porsche shop for that job.

[kidrock]

If the car is trying to start (and you claim it has spark), then it may be a fuel issue that you need to chase down. Try introducing some carb spray into the intake and see if it starts.

[david-j-w]

Hi, I sprayed some easy start into the intake and she fired and ran but immediately cut out.

[Walt Fricke]

I'd check fuel pressure back at the fuel rail. There is a plug there you can remove to attach a pressure gauge. That ought to tell you if the fuel pump is pretty much OK, along with filters and anything else in between pump and injector.

This sounds a bit like a cylinder head temperature sensor issue. Put a 500 ohm resistor across the ECU side contacts on the plug where the CHT sensor plugs into the wire loom up over the left rear side of the engine, and see what happens? Or search here for a resistor value not based on a foggy memory.

[david-j-w]

Thanks a lot, that's a bit above my head to be honest. I can certainly get hold of a pressure gauge tomorrow so will try that. I have had that nut off to see if fuel is coming through, there is a ball bearing inside it.

[ischmitz]

It could be this simple: The injectors on 3.2 like to get stuck shut if the car sits for a long time. That makes starting impossible or the engine misses when some fire and others don't. Once you introduce fuel (starter fluid) the engine will catch. So you have spark.

Use a screwdriver handle and tap the injectors gently while someone else cranks. That gets them unstuck. If that doesn't help verify your fuel pump runs (DVM onto FP fuse) and that your fuel filter isn't clogged

Ingo

[david-j-w]

tapped the injectors and tried again, still no start. Fuel filter is ok as well. Checked fuses and all ok.

I had the alarm disabled and immobiliser disabled a few weeks, and I thought that was it. But just found a SACHS one under the front panel in boot, if I reading right that's where Porsche put the original one? I thought if I am getting enough fuel and spark then that alarm hasn't to be not working? I don't have any zapper for it either.

[kidrock]

FWIW, I've had a similar issue where the fuel pump "hummed" when I turned the ignition switch to the AUX position. I falsely believed that the hum was indicating that the pump was working. Replaced the pump and problem was gone.

Check the pressure. Could be something as cheap and simple as the filter. Could be the pump. Could be the regulator. A pressure test will tell you if the fuel issue is "upstream" or "downstream" (like Ingo pointed out, it could be a bad injector).

It certainly sounds like a fuel starvation issue.

[Walt Fricke]

My experience with earlier Porsche fuel pumps is that they were nice and silent. When they started to make any noise, I got worried. But testing is the way to go, lest you buy a new fuel pump to replace a perfectly good old one, and find you haven't solved the problem.

[gtc]

There are a number of threads on 3.2 no-starts that outline the testing of your sensors and ignition components.