vanster

Yesterday my trusty 86.5 would not start....It always starts! I checked everything then went to the fuel pump relay. By passed it with a jumper and it starts. I have a box of relays tried them all..nada
We do my local Porsche parts house and got a "used" relay...still won't start. Jump it and it fires right up. The fuel pump has about 30k on it.
Any suggestions?

Ducman82

Hmmmm could be signal from the computer?

GT6ixer

Not sure about the '86.5, but does it have a fuel injection relay? If so try replacing it with a new one. No other relays (at least on the early S models) will swap with it. That's what kept me off the road a few days this summer

Kevin in Atlanta

Relay gets it's marching orders from the LH. If bypass works 99.99% chance it's the LH computer.

Mrmerlin

put your computer in another 86.
also check the grounds at the rear of the hatch

vanster

I just tested the relay and it's good, replaced it with another good one and the issue persist. I'll go for the grounds in the hatch next. It could be the LH which I believe is from an S4 not an S3.

davek9

S4 LH in an S3

vanster

There isn't much S3 left in it. Big chunks are S4....Don't tell anyone.

davek9

OK I won't
However for future posts for those searching and following along at home, would be good to have stated that up front, just a thought
And... if that S4 LH was from an '87 it is the most likely suspect, a known failure

Dave

vanster

You are correct and I wasn't thinking in that direction. As I recall the later LH's are more prone to fuel pump failure than the 85/86.

Speedtoys

Ill be at DIY Or Die in san jose all afternoon if you wanna come swap it..

FredR

The S4 LH units have a secondary tile in them that fires up the fuel pumps- when it is working! Sounds as though you need to get the LH off to Louie for a JDS rebuilt unit or at the very least to get it tested.

If you have a custom programmed EEPROM in the LH you will need to advise Louie of such.

Lizard928

Have your LH rebuilt by JDS.

GregBBRD

Lost power or ground to fuel.pump relay. You can put common test light across "85" and "86) of the fuel pump relay socket (while cranking) to confirm this (relay out)..Then test each "85" and "86" individually to ground (while cranking) to see if you have power on either.

This will tell me a bunch.

While people are saying that loosing signal from LH to fuel pump relay is a common problem, I've never seen this.....and I've seen a bunch of LH failures. I can send you up a rebuilt JDS computer to test, if necessary. (I'm thinking I would have put a rebuilt in, BTW.)

I'll call in AM.

dr bob

The ground for the fuel pump is there regardless of relay or jumper supplying current. While the grounds do need to be clean, they aren't the cause of your problems.

Note that the LH connection to the FP relay is an open-or-ground signal, pulled low (towards ground) at LH terminal 20 (BR/RT) to cause the relay to close via W15 and relay terminal 85. Power to the relay is supplied from the 15 bus when key is in RUN or START position. Confirm the ground to the LH module as a possible cause. MP IX