DME not powering fuel pump relay

immusicman · 05-09-2010, 05:16 PM

I have a 944 with 64k miles that has sit for the last 2 years and it wouldn't start. I jumpered around the fuel pump relay and the fuel pump will run if I do that. Here is the problem, the circuit that comes from the DME module to power the fuel pump relay is not getting power, thus fuse number 8 has no power because this is where it gets it frrom. So is it the DME? Or is there a TDC sensor or position sensor that may not be reading a pulse preventing the DME from powering the fuel pump relay? I noticed I have not tachometer when cranking it or even after starting it with starting fluid. I noticed no radio also which according to diagram, it looks tied together somehow. And, My charging or battery light is staying on when the key is out of car, if I turn key on it goes out. Major draw on battery with no key in it. This sounds like the alternator to me, but I am all ears. I wanna fix it right. Thank you for your help.

immusicman · 05-09-2010, 06:41 PM

Ok, after reading some posts I see there is a reference signal sensor which I have not checked yet. But does ANYONE have a trouble shooting tree or suggestions on how to check out what would cause the DME to not power the fuel pump relay? Thanks

ddbach · ddbach's Garage

Welcome,

Look here, this post has a great list and excellent links that should help.
Let start a NO START checklist

Others wil have more advice too.
check Clark's Garage too.

immusicman · 05-09-2010, 07:00 PM

Thank you for that information. I am curious to know does the reference sensor have to sense a pulse or rotation of the engine before the dme will allow the fuel pump relay to energize? If so, that would be why my tachometer isn't jumping or working at all also? Someone told me to replace the DME but I don't have any evidence yet to blame it on that. Thanks.

Grandad#3 · 05-10-2010, 10:14 AM

Hello, Read the article in clarks garage about the DME Relay and how to make a jumper for temp. use. You should get about 1/16th" jump in the TACK gage with the engine turning 200 rpm on start. All we know is that you have a 944 with 64K, which 944, and year do you have? Does any lights work on the car? Check all fuses, some may look good but still be bad. I hope your fuse box itself doesn't have shorts in it. Mine did and I had to replace it on an 85.5 na. You are leaving a lot of information out that we need to help you. What have you already done on the car? Have you drained out the old fuel for one?

DME Relay Information and Testing

Cheers,
Larry

Jtilden · 05-10-2010, 10:34 AM

from what you have posted it seems your next step would be to disconnect and clean the reference sensors...try that and let us know what happens

immusicman · 05-10-2010, 04:31 PM

Thanks for your suggestions. Yes the tank has been dropped and cleaned and a new fuel pump was put on which will run when jumpered over. As stated, I believe it is terminal 6, don't qoute me on that cuz its not right here in front of me, but this terminal on the fuel pump relay is fed by the DME and it is NOT getting power. I know it is supposed to and from what I have read it is supposed to have a reference crank signal that is sent to the dme to trigger the power to the fuel pump relay. I bought a new reference sensor today cuz I got it for less than half price and I am going to just replace it tomorrow. I really believe somehwere in this is the problem I have a 1984 944 Non turbo 2.5 I believe. I KNOW I need to get that tach jumping and reference reading to the dme then I will ask from there. My second issue is something seems to be really drawing the battery down. I bought a used alternator because I suspect there may be something going on there where it set for so long. I wouldn't have just bought one, but the price was good so I got it. I know there is probably another problem because even with the alternator disconnected I still get a drain. I will run that down when I get it running. Then off to the paint shop! I can't wait. I have a couple grand to drop into the paint work and I suspect that will just barely get it done..it is only faded, no rust. Any other suggestions I appreciate! J

immusicman · 05-11-2010, 11:29 AM

Replaced the Reference sensor and checked the speed sensor, both ok. I have a pin identification diagram and I am going to check power to the dme right now. I dropped the fuse panel down and noticed two wired behind it that are not plugged int to anything. One says 19 on the sleeve and it is black and red, the other says 20 on the sleeve and it is white and black. I have no idea where they go but wonder it this is a large portion of my problem. Unfortunately, even the shop manual doesn't show where each wire plugs into the back of the fuse box, it assumes they are already connected..how silly that you can't have a diagram to show where each goes! In a perfect world the wires coming to the back of fuse and relay panel would never come loose, but these two wires are loose and I have no idea where they go. Thanks.
j

akron · akron's Garage

Did you get good results? I am interested because I have a 944 where the previous owner wired a switch in place of the original wiring for the fuel pump. I would like to get it back to normal wiring/functionality and am interested to see if you had a good outcome.

Rasta Monsta · Rasta Monsta's Garage

Quote:

Originally Posted by akron

the previous owner wired a switch in place of the original wiring for the fuel pump.

Don't you love it when a complete stranger tries to burn you to death?