Jared944

So, my first question would be if the fuel pump is running when your key is in the on position (I can hear mine humming from the drivers seat). If not, then check for +12V (or near 12V) at the fuel pump with the key in the on position. If you have no electricity back there, it could be the relay.
But your not done yet! Pull the relay... again turn the key and see if you have electricity at the relay. If you do, than the relay is the problem. If not, than the problem exists between the power supply and that point (probably the DME).
Basically, you now need to trace the electrical signal from the fuel pump to the DME, and see where the signal stops. This point is the problem area.

wesmc3

I had the same problem on a miata two weeks ago. The Miata and the 944 electronics are similar. I found the problem was an AFM going to dead short.

Zero10

So, if its the fuel pump then it starts and runs fine with the fuel pump jumpered? Didn't think so.

The fuel pump runs when cranking and when the engine is running, BUT, the engine has to know it's cranking. This could still be speed / reference sensors. Does the tach wiggle when you turn it over? No spark is another good sign these are your problem.

vro944om

i know it may sound bad to most of you, but this is great for me, the Tach does not jump when i crank it... so the spped and reference sensors are bad or need adjustment... yay, another ray of hope in this disaster of a project car


and thank you jebus for clark's garage

Zero10

They must be _THE_ most common no-start causer, with bad DME relay as a close second.

They can be mis-gapped, the connectors can be broken, or the sensors themselves can have had a close encounter with the flywheel and be demolished.

You can check the function of the speed sensor using a volt meter, set it to volts _AC_, you should see a reading of ~7-11VAC when cranking. The reference sensor cannot be checked so easily, but the gaps are fixed on a bracket. Removal of the speed/reference sensors drives many to insanity, on occasion removing the entire engine from the car when things really go wrong. Patience and lots of penetrant is key for getting them out safely (only remove them if necessary).

Check the connectors closely, un-plug them and re-plug them. Heck, swap them (sometimes the PO will swap them around trying to troubleshoot a problem) and try again. Quite often the cast pieces of the connector will brittle with age then shatter, causing the pins to break free of the little remaining bits of plastic and no longer make proper contact.

vro944om

tomorrow im gonna check the speed and ref. sensors, measure them up, make sure they're not broken, put em back on, then check the pressure regualtor, those are my last 2 options.

apierce918

does it have a timing belt?

vro944om

yeah, but hasnt been replaced yet

apierce918

add that to your list, last thing you want is for it to go right after you solved everything and it revs the first time. ask me how i know....

vro944om

ouch.... yeah thats the first thing im doing after it actually starts... and then the water pump... then paint... jeez.. my car is lucky it's a porsche

McLovin69

is the fuel line clogged?

vro944om

no the fuel pump doesnt start at all, but jumpered it does. im sure its the speed and ref. or press. regulator

CPR

It is the S/R sensors...that is all. Nothing more, nothing less. If the comp does not get a signal form the sensor it will not close the relay allowing the fuel pump to cut on.

vro944om

oh and i might have fried the computer... i accidentaly arc welded a wrench from the + to - side of the battery...while it was connected! can i even buy a new one?

Zero10

That won't screw up the DME. Reverse polarity may, but shorting out the battery won't. I'm not sure I follow you though, since in your first post you said you replaced the DME, now you are asking if you can even get a new one?