Diagnosing No Gas Problem

3sonfather · 12-24-2005, 12:01 PM

So I roll into the garage yesterday, turned off the ignition, then a split-second later I go to restart it realizing that I needed to back the car out. It sputtered to a stop.
Following some earlier posts, I verified voltage to the coil and the fuel injectors - check, 12V.
I found that the second fuse from the right on the aux fuse box was blown (I'm guessing that's for the fuel pump). I replaced it and still no start. So now I'm questioning the DME/fuel pump relay. I jumpered contact 30 to contact 87b and checked voltage to fuel pump - no voltage. I then ran a wire from the battery to the + terminal on the fuel pump, still no action so I'm thinking the pump is bad. I replaced the pump with a known good one and still no action. What gives? I'm afraid something else got cooked. What else should I check?
Thanks & Merry Christmas
Scott
84' 944 na

Moneyguy1 · 12-24-2005, 12:12 PM

"Replaced witha known good one"..

Scott..Last year I had a similar experience..almost identica; Came home, parked the car, turned off the ignition, decided to put the car in the garage and bingo..would not start. Checked spark..OK..WOuld catch with a spritz of ether so ignition and timing OK. Fuel pump...ran wire from battery to pump...NADA...Bought brand new Bosch pump..installed along with new fuel filter(s) and relay..nada...New pump was bad!! Had to send it back for replacement.

That was a year ago, car has been sitting since then with a monthly "crank the engine just to keep things lubricated" session. Maybe someday I will completely tear the fuel system apart but than again maybe not.

Seems as if there is a design flaw in the fuel system that has taken two decades to show up. So many posts recently about similar problems.

If you find a solution, please post it and make a LOT of folks happy!!

Merry Christmas!!

Bob in Tucson (76 degrees at 2:13 PM Christmas Eve..lousy sledding)

Granite 944 · 12-24-2005, 12:27 PM

Remove DME relay, jumper points 30,87b, and 87 all together, and try it. If she don't a go then, come back and let us know.

3sonfather · 12-24-2005, 12:34 PM

76 degrees; ya just had to rub it in Bob.
Granite, after the jumper do I need to engage the ignition switch to hear the pump?

earlr85944 · 12-24-2005, 12:41 PM

when you installed a known good pump and applied 12v directly to it in the car did it run and start the car?

Granite 944 · 12-24-2005, 12:44 PM

No, it should fire the pump up continueously as soon as jumpers are in. However, you blew a fuse at the one point. If you get nothing from the pump again, check that fuse again. There has to be a reason for that. A short somewhere between fuse block and pump, or blocked pump, check valve. If you blow the fuse again, your pump is probably seized up and needs replacing. just guessing here.

Granite 944 · 12-24-2005, 12:52 PM

Also make sure the fuse contactors are clean,and you get the voltage in and out of that fuse. Should be the red fuse (16amp). Take the +12 line from battery to pump off, especially, if you didn't put in an inline fuse to test it with.

3sonfather · 12-24-2005, 06:04 PM

Ok, an update.
The fuse that was blown (second from right) powers the windows so forget any relation that may have had. The fuse second from left powers the fuel pump and was shown intact. I jumpered the forward end of the fuse# 2 junction with fuse# 3 as stated by SoCal in an ealier post as this has the same effect as hot wiring the DME/fuel pump relay socket. The fuel pump hummed to life and the car started up and ran just fine. Now after pulling the jumper, the car stalled; no energy to the pump. I checked the contacts of the relay as stated in Clarks Garage and it functions fine. I'm guessing now that the DME itself decided to call it a year. What do ya think?
Scott

3sonfather · 01-04-2006, 05:41 PM

Another update... I have tried the following tests and still no go with the fuel pump.
1. Swapped DME
2. Installed new DME/Fuel pump relay
3. Swapped fuel pump
Possibilities: alarm module ?? or ignition switch??
For now I have fashioned a single pole switch between aux. fuse# 2 and 3 so I can get around town.
Any ideas on this mystery?
Thanks,
Scott

SoCal Driver · SoCal Driver's Garage

Think your DME relay socket may have a loose contact or the wire from the socket's pin to the fuse may be loose. Have to drop the relay mounting down and check. Take the ground off of the battery first.

Granite 944 · 01-04-2006, 06:36 PM

OHHH, this REEKS of FUSE BLOCK/PIN problems.

Oh yeah, it IS the second from the left. Depending on how ya are all lookin at it.

"For now I have fashioned a single pole switch between aux. fuse# 2 and 3 so I can get around town."

Hmmm........from where to where? pics, or a very good description of HOW and WHERE ya did this....please.

SoCal Driver · SoCal Driver's Garage

The aux fuse block is the 9 fuse unit. Count from the drivers door. Fuse 2 is for the fuel pump. Fuse 3 is for one of the radiator cooling fans and is always hot. Jumpering between these you can run the fuel pump with out taking the DME relay out. The second set of contacts in the DME relay power the fuel pump when the DME closes them.

So check the wiring between this fuse and the relay socket and the wire that comes from the DME itself. It's pin #20 on the DME connector. #85b on the relay. The DME grounds this out to activate the coil that closes the second set of contacts.

Note that wires have been known to break off the backs of the pins at the DME plug.