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Have spark but fuel pumps not running – except when jumping terminals on R61
Hi all, I’ve owned a 1991 3.3 Turbo for over 13 years and throughout this time have resolved many issues due to this invaluable forum. However, I’m stuck on this latest issue and welcome any advice.
The car was running beautifully when I put it back into storage and disconnected the battery two months ago. Last week I reconnected the battery but instead of firing up immediately, as it normally does, it wouldn’t start.
A quick summary:
- New battery & front fuel pump
- New plugs & good spark (pulled spark plug wire & grounded spare plug)
- Fuel volumes & pressures all in spec (WUR rebuilt 6 months ago)
- Fuel pumps not running when engine cranking
- Flywheel speed sensor connector in engine bay ok
- New boost pressure switch – no change when wire grounded
- Fuel pump fuses ok
- Fuel pump relay swapped with working (53) sunroof relay
- R61 terminal 30 has 12.6 volts with key off
- R61 terminal 86 has 12.35 volts with key on – it’s my understanding this is the fuel pump relay ground through the turbo control unit?
- Jump terminals on R61, key ignition and engine starts immediately
- Idles well, as per normal, and reaches warm control pressure (4.5 bar) within 3 ½ minutes (have fuel pressure gauge permanently connected to fuel distributor)
Check the flywheel sensor. They tend to crack and the connection.
The Turbo Control Unit under the drivers seat won't trigger the fuel pumps and the EZ69 ignition module unless it gets a signal from the flywheel sensor the the engine is spinning.
Thanks Paul, I do have spark and the engine runs so assume the Turbo Control Unit must be getting a signal from the flywheel sensor to do this - for spark at least?
It is correct that the crankshaft sensor is in order when the ignition spark is ok .
The error is apparently due to the fact that the terminal 85 on R61 is not triggered. It is the ground signal from pin 12 (br/ye) on the turbo control unit.
There are several reasons why the ground signal is missing. On the one hand, the soldered relay on the board of the turbo control unit may have failed or one of the input signals on the turbo control unit is missing.
Since you seem to have some knowledge of automotive and 964 turbo electronics check the ground output on pin 12 and the input signals (terminals 15, 30,31,50) according to the wiring diagram.
Am i right if i assume that you already connected the white wire at the pressure switch on the intercooler to ground for test purposes?
Many thanks Fritz. Yes, i have already connected the white wire at the pressure switch to ground with no change. The switch is new and I've found previously that if faulty the car almost starts and then dies. With my current issue it cranks well with no sign of starting.
Very interesting that you've pointed out terminal 85 on R61 not being triggered. Last week I had 0v at terminal 85 with key ON. Yesterday I had 5v with key ON. Thought this was airbag related which I understood to be disconnected so ignored it.
I have done some testing of the PLUG that goes into the turbo control unit but I'm unsure of what the values should be:
- Pin 12 Actuation Fuel Pump 4.98v with key ON, 4v when cranking
- Pin 11 terminal 15 12.34v with key ON
- Pin 6 terminal 30 13.24v with key OFF
- Pin 10 terminal 31 to be tested - what value here?
- Pin 4 terminal 15a 10v cranking
I'll look further into the ground signal from the brown/yellow wire (pin 12) on the plug going into the turbo control unit.
Turbo control unit test below (ran a 9v battery over the coil solder points). Please keep the suggestions coming.
- Pin 12 switches the 12 volt plus from terminal 86 R61 to ground. Here should be 0 Ohm resistance to ground measurable when the starter turns.
- pin 11 terminal 15 is o.k., this is switched plus, so battery voltage.
- pin 6 terminal 30 is battery plus, directly from the battery. here should also be 12.x V, 13 and more can only be when the engine is running, so charging voltage is present. Something is wrong here.
- pin 10 terminal 31 is ground, so 0 Ohm resistance against ground or 12,x V against terminal 30 should be present.
- pin 4 terminal 50 is the starter signal, the value is slightly lower than battery voltage because the starter is already drawing current, so 10.x V is ok.
Check the voltage on your airbag connection harness. Pull the side view access panel and pull the Center Console Cup.
I tossed my airbag control unit and jumped the wires to fire my fuel pump.
Check the voltage on your airbag connection harness. Pull the side view access panel and pull the Center Console Cup.
I tossed my airbag control unit and jumped the wires to fire my fuel pump.
The switched plus on terminal 86 at R61 comes from the airbag control unit. If there are 12,x volts at ignition on there is no problem caused by the airbag controller.
Scott & Fritz, thanks to you both. I will definitely check the voltage on the airbag connection harness.
For clarity please confirm the terminals on Relay 61:
- terminal 85 is the ground signal from pin 12 (br/ye) on the turbo control unit
- terminal 86 switched plus on comes from the airbag control unit
Correct? I'd read somewhere it was the other way around.
I was getting the following from my Relay 61:
- terminal 30 reading 12.59 volts with key OFF
- terminal 85 initially reading 0 volts and the following day 5 volts with key ON. Something is wrong here.
- terminal 86 reading 12.35 volts with key ON.
I will check the airbag connection and go over the pins in the turbo control unit with a multimeter again tomorrow and report back.
Fritz - I had 13.24 volts at pin 6 terminal 30 battery plus, directly from the battery because it was on the trickle charger at the time. Was taken off for all the other readings in the turbo control unit. So pin 6 is OK.
Scott & Fritz, thanks to you both. I will definitely check the voltage on the airbag connection harness.
For clarity please confirm the terminals on Relay 61:
- terminal 85 is the ground signal from pin 12 (br/ye) on the turbo control unit
- terminal 86 switched plus on comes from the airbag control unit
Correct? I'd read somewhere it was the other way around.
I was getting the following from my Relay 61:
- terminal 30 reading 12.59 volts with key OFF
- terminal 85 initially reading 0 volts and the following day 5 volts with key ON. Something is wrong here.
- terminal 86 reading 12.35 volts with key ON.
I will check the airbag connection and go over the pins in the turbo control unit with a multimeter again tomorrow and report back.
Fritz - I had 13.24 volts at pin 6 terminal 30 battery plus, directly from the battery because it was on the trickle charger at the time. Was taken off for all the other readings in the turbo control unit. So pin 6 is OK.
Cheers
Yes, every point is correct, I have not seen any error.
The question regarding terminal 85/86 on R61 is self-answering, because you can measure switched PLUS AGAINST GROUND on terminal 86. So not the other way around and no failure of the airbag module.
To anticipate it terminal 15 on the turbo switch unit comes from the alarm control unit, so there is no problem with the immobilizer.
As I wrote in the first post, your problem is the lack of ground at terminal 85 R61, so the R61 for fuel pumps is not triggered. Put temporary ground on the terminal 85 and when i'm right the car should run.
Hi Fritz, I've retested the pins with a new multimeter and all are OK except pin 12. It reads 1 ohm with key OFF but there is no reading at all when cranking.
The wire in pin 12 feels loose in the plug compared to the other wires so this may be the problem.
How best to put a temporary ground on terminal 85? The relay also needs to be in place?
Years ago I had a O2 Sensor short out my DME on a 91 964. It left me stranded in New Mexico.
i think i was 26. But I made it back to Missouri same day in a U-haul truck-trailer. That dang thing ran out of fuel in Oklahoma. No fuel light.
Good Porsche from LA.
The O2 plus a White wire from the intercooler speed sensor that sends a signal. The rest is ignition. You know that's good cause you have spark.
You'll need to ask Fritz how to diagnose the intercooler sensor and the O2 Sensor. I'm just a parts changer not a engineer or mechanic.
Is this the control unit? ....
FVD
Turbocharger / Multifunction Control Unit 965 3.3 L - 1991 and 1992 Only
Part #: 965 618 130 00
Expected in 1-3 days
Warehouse Germany
$ 759.00
Hi Scott, the O2 sensor is new and I have power to it's connector. Car has consistently idled well and after a few minutes Innovate AFR sits around 14.7 although I do need to have verified with CO test.
The boost pressure switch on the intercooler is also new but I bypassed it by grounding white wire to eliminate as cause for no start.
Yes, that is the Turbo Control Unit aka Multifunction Control Unit in the PET.
Hi Fritz, I've retested the pins with a new multimeter and all are OK except pin 12. It reads 1 ohm with key OFF but there is no reading at all when cranking.
The wire in pin 12 feels loose in the plug compared to the other wires so this may be the problem.
How best to put a temporary ground on terminal 85? The relay also needs to be in place?
Cheers
You may either use 4 flat receptacles with a branch. With this you can plug in the relay and connect a ground wire to terminal 85. It is probably necessary to buckle on or to remove the three superfluous branches for space reasons.
Another possibility is to remove the cap of the relay and solder a wire (to ground) to the inner contact of terminal 85.
Maybe it is a final solution to re-solder all accessible contacts on the turbo switch.
Thanks Fritz. It will probably be easier to find the lack of ground at terminal 85 R61 than to track one of those down. I removed pin 12 from the plastic plug but it was only a bit loose within the plastic plug - the actual wire connection into it appears ok. I cleaned with some contact cleaner and reinserted into the plastic plug before connecting tightly to the turbo control unit. But it has made no difference, the lack of ground is elsewhere.
02-28-2023, 06:19 AM
Have spark but fuel pumps not running – except when jumping terminals on R61
