87 Carrera NO Start issue

[carrue529]

I have done a search and tried the various checks and the car will not start 87-911

Coil Test:
spare plug in wire #1 from coil, NO Spark while cranking BUT it sparked as the IGN was turned off?
using a test light on coil it turns on solid bright when cranking engine but it does not pulsate?

Battery:
New (5mo) Optima Red 12V

GND: clean all and new transmission and battery ground cables
Fuses: 4 ~8 @ 11.55V with IGN on (All new fuses)

Fuel Pump:
2yrs old when I jump fuel pump fuse it whirrs on, turn on IGN to bypass DME car started only one time tried it again no start

DME: I have three of them and swap between them no luck.

IGN Switch: NEW from PP (several days)

Starter: Hi-Torque rebuilt within the last 6mo. ( I thought that was the issue)

Flywheel Sensors:
check one of the sensors from rear of car on left side it has two wires coming from connector (white) measured 4.27V (AC)with IGN cranked. other 2 sensors no measurement

DME Computer was re-built 5yrs ago

ANY HELP or direction would be appreciated
THANX

[pjv911]

I can say that the coil will supply one spark with a key cycle. So if it has no spark while cranking then the issue is in the primary circuit of the ignition.
Have you checked the square wave signal from the crank sensor? That is the first place I would look to rule out. A cranking voltage test is not conclusive.

Kurt Williams

[Joe Bob]

Does the DME relay click when turning the ignition to on? If not, your not getting switched power.

Does it click constantly while cranking? Your switched power is shorting....

[Joe Bob]

BTW, the "PET" has a diagnostic for the 3.2 engine. I believe that the 3.2 DME and the later 964 trouble shooting is the same.

You need to see constant 12v in the DME harness at a certain pin (18), then power in another pin when the key is turned (37). If you have it at the harness reconnect the DME and test for power at the 6 pin connector BEFORE the DME relay. It's female pin #3.

I just went thru this BS on my ride and it's a pain for a novice, but easy once you have help/direction. Again, this for the 3.6....3.2 MAY be different
Feel free to PM me.

I was able to download the PET for free a number of years ago. Don't know if the Porsche lawyers have stopped it or whatever. Probably like file sharing of music....no one REALLY knows the rules.

Do a search on my name or ischmitz for recent threads, it has specific pin #s but again.....yours is a 3.2 DME and not a 3.6 like I was working on.

[Wil Ferch]

What is standby voltage on battery? If 12V...much too low. Should be 12.6-12.7 range. A battery at 12V is about at 25% charge. Start with the basics.

[Don Ivey]

Just because the ECU is only five years old, doesn't mean it can't have gone bad. Try, if possible, to interchange one that you know is good, and see if that is the problem. When I got mine rebuilt last year, the guy at ****** told me they break all the time; it's not unusual (unfortunately).

Don IVey
'87 Carrera

[pjv911]

Originally Posted by Wil Ferch

What is standby voltage on battery? If 12V...much too low. Should be 12.6-12.7 range. A battery at 12V is about at 25% charge. Start with the basics.

With key in on position the battery voltage will reflect any current draw available (Example: stereo power amp or fuel pump running).
So the voltage he described only shows that it is sufficient to power his engine management.

[carrue529]

guys thanx for the input so far, Don I'm starting to lean torwards the ECU

I bumped started the car (rolled it down the driveway) and for the next two days (5 starts)the car started fine after that refused to start. bumped started again to get home (wrk prkng on a small hill) and car has started the last two times. this has been going on for a while just want to find the issue.

I will need to find some-one in my area with a Carrera whose ECU I can use or is there somewhere I can take my ECU to have it checked? or purchase aother inexpensive one?

Battery Voltagte is at 14v when car is running +12.5v when stationary.

DME clicks when turning on, sencond click when turning engine (I removed the DME cover on one of the relays)
how do I check the square wave signal from the crank sensor, what do I need ?

thanx again for your input

[Zeke]

Originally Posted by Joe Bob

I was able to download the PET for free a number of years ago. Don't know if the Porsche lawyers have stopped it or whatever. Probably like file sharing of music....no one REALLY knows the rules.

The PET is on the NET @ Porsche Classic Original Parts Catalogue - Classic Genuine Parts & Literature - Porsche Classic - Dr. Ing. h.c. F. Porsche AG
It's very slow, but it's all there.

[rick-l]

Originally Posted by carrue529

Coil Test:
spare plug in wire #1 from coil, NO Spark while cranking BUT it sparked as the IGN was turned off?
using a test light on coil it turns on solid bright when cranking engine but it does not pulsate?

Hope that Ingo or scarkeller check in but I think this might tell you which sensor is not working. Like the DME knows the engine is turning but doesn't know where TDC is.

[Jay Auskin]

Have someone wiggle the wires on the flywheel reference and speed sensors near where they connect to the sensor while cranking. These get brittle over the years from heat, and cause bad connections. The intermittent starting leads me to believe this is your problem.

Oh yeah...you can buy BMW replacements at a discount over the Porsche part numbers. I believe they have a slightly longer wire, which isn't a problem.

[pjv911]

You would need a scope to check the square wave

[steely]

Originally Posted by carrue529

Flywheel Sensors:
check one of the sensors from rear of car on left side it has two wires coming from connector (white) measured 4.27V (AC)with IGN cranked. other 2 sensors no measurement

Just to verify, the white one is the O2 sensor.
If the other 2 have crumbly insulation, I'd replace them both (speed and ref sensors)
+1 on the 'scope unfortunately

[slodave]

The white one is should actually be the CHT sensor. I just finished a valve adjustment and apparently bumped mine. I had no start today and after Dave from TRE talked me through some things over the phone, he had me make sure they were firmly connected. Once I did that, my car fired right up.

[ischmitz]

If your car issues a spark when you turn the ignition to OFF the DME is damaged. This is a very simple conclusion and tere is no doubt. Here is what is happening:

When you turn the ignition to RUN the coil receives +12V through the ignition switch and permanent GND through the shorted DME (bad ignition stage). There is constant current flowing through the coil. Once you turn the ignition to OFF you interrupt the current though the coil, the magnetic field is breaking down and the coil will issue exactly one spark.

With a properly working DME the GND is only swithed on for the dwell time (several milliseconds) and once the ignition stage switches the GND off a spark is released. The bottom line is your DME needs repair. Contact me via PM or at 3.6(at)cox.net if you want to your DME repaired.

Ingo

[ischmitz]

Originally Posted by pjv911

I can say that the coil will supply one spark with a key cycle.

Kurt, this is only true for a traditional Kettering ignition and if the points happen to be closed. Every time you cycle the ignition switch you energize the coil and cut the current flow again. This is why one spark is fired off.

With a modern transistorized ignition (DME) or with the CDI ignition setup there won't be the single spark per key cycle.

Ingo