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My 1988 SPG, has a history of intermittent no-start. Going through this board shows that this too common a problem for us. For the benefit of some one that may encounter this problem, here's my experience.
Intermittent problems are among the most challenging. How does one know that its fixed, when it can "go away" on it own only to happen again.
On my car I was "lucky" to have it stay in the no-start condition for a long time. I changed the main and fuel pump relays (many times), bypassed the electronics to the fuel pump with a jumper wire at the fuse panel (pump ran, still no engine star). With Bentley's manual on hand, I learned that the fuel pump *AND" fuel injectors will not operate if the ECU does not receive the "engine is cranking" signal from the ignition amp (on the wheel well, next to the APC unit). This explains why jumping the fuel pump to operate did not result in a running motor. But wait, there's more.
I checked the voltage from the ignition amp to the ECU (following Bentley's, page 371-63), found a signal within specification, but I changed the ignition amp anyway since I had a new one on hand, and wow, the car starts. Happy I was thinking I had finally solved the problem. However, just minutes later the motor would not restart, just once, but on second attempt, just a minute later, it did. The no-start problem did not reappear for more than a year, so naturally I chose to believe that the problem was solved, but always that little annoying concern that there was that one no-start right after replacing the ign. amp.
Then it came back.
This time I carefully checked the Bentley's circuit diagram, and realized that there is a signal from the main relay to the fuel pump relay (bin 86 on the fuel pump relay) that needs to have voltage to close the 87 & 87b circuits on the relay that then energize the fuel pump and the fuel injectors. In between the main relay and F.P. relay this brown/white wire is in series with the turbo pressure switch (Located underneath the steering wheel, behind the wiper relay. This is equivalent to the fuel cutoff switch on the 9000). I had a very difficult time disconnecting one of the 1-pin connectors of this circuit (near the ECU), suggesting that corrosion that could be the cause of the intermittent connection.
I've cleaned the contact, bypassed the pressure switch (I don't drive in such a way to encounter fuel cuttoff events). The car starts just fine.
But, consulting Bentleys, there are other possibly ways to have a no-start issue that takes down the fuel pump and injectors. If the ground signal from ECU (pin #17) is not received at fuel pump relay pin #85, pins 87 & 87b do not close, and no power to fuel pump and injectors.
Also, ECU pin 21 must provide ground to main relay pin #85 for main relay to send power to fuel pump relay pin #86 (this is the brown/white wire that goes through turbo pressure on the way to the F.P relay).
I'll resume driving the car, but I'll keep tools on hand to drop the knee panel to access the circuits if need be for further investigation.
Is the problem solved? I hope the corrosion at the 1-pin connector was the problem, but ya never know.
hope this helps!!
posted by 68.55.22...
, Sun, 11 Dec 2011 21:51:00
, Wed, 24 Aug 2011 17:12:03
, Sun, 21 Oct 2018 03:42:10
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