Fuel problem

[marcsalleras]

1986 911 3.2, been running perfect, other day it turned over normal but wouldnt start, pulled a plug and its getting spark, did a upper and lower rebuild with a master porsche tech 6 months ago so i know the engine is fine, have no smells and leaks.......let it sit a day and it ran normal again....ran it another day or two and now its doing the same thing in the garage....i have a spare DME relay i just put it to see if that was it and it kept doing the same thing, turning over perfect but not starting up.............my minds now on the fuel pump, i know i can test the voltage on it to figure if it's running fine or not but is there any other way i can check? just curious.....or if you think it's something else feel free to put your two cents in

[E Sully]

I would say the DME itself is fine or you would not see a spark. I would put a voltage meter on the pump and see if it is getting voltage when cranking, it will not get power if the engine is not spinning. The relay can be jumped out to see if the fuel pump runs. The DME relay is notorious for cold solder joint problems. Is the spare relay you tried new or used? Have you checked for corrosion at the the fuel pump fuse and terminals?

[marcsalleras]

I thought the fuse for the fuel pump was essentially the dme relay? i've looked around for a fuel pump fuse and I can't find one on this car........and corrosion at the battery terminals or? testing voltage on fuel pump tommorow

[DRACO A5OG]

Ref and/or Speed Sensor.

It will crank but will not engage

[E Sully]

From the wiring diagrams the power for the fuel pump goes through the dme relay and then to fuse 3, 25 amp, in fuse box 1 in the trunk.
The reference and speed sensors must be working or there would be no spark.

[Joe Bob]

Is the relay click or continues clicking when turning the ignition to "on"? Continuous clicking is a switched power isuue....

Does it click when turning over? Same as above.....

Do you have spark?

Do you have power to the coil(s)?

[DRACO A5OG]

Originally Posted by E Sully

From the wiring diagrams the power for the fuel pump goes through the dme relay and then to fuse 3, 25 amp, in fuse box 1 in the trunk.
The reference and speed sensors must be working or there would be no spark.

Hmm, true.

It would be easier to swap out the FP.

OP, do you have a buddy you can swap the DME to take it off the list?

J

[Joe Bob]

A shot a quick start into the intake while cranking the engine will tell you if it's a fuel issue. If it coughs ore even starts....it's a fuel issue. No joy, it's spark...

[marcsalleras]

getting spark, no spare dme to change out and see if that's the issue, speed sensor and ref sensor changed when i did the complete engine rebuild...........i'm betting its the fuel pump......i just thought it was odd that it would work one day then not the next......i expected it to go slowly but then again that doesn't really make sense for a fuel pump goes "slowly", itll either work or not work....so i'm expecting it gave out on it's final leg

[gregwils]

They don't go slowly, they stop. You can sometimes wake them up with a small tap from a hammer. However, if you have to wake it up, it's trying to tell you something.

I actually just replaced the pump on my '86. I think it was original and figured it had seen enough action and I didn't want to mess with it during the driving season.

[marcsalleras]

scratch that, i've got fuel and compression...........no spark! checked coil, dme relay, tested that power was getting to dme, new fuel pump fuse, no corrosion on dme......What now??? I mean if the dme isn't showing any corrosion, doesn't that mean the likelyhood of it being broken is a little low?