Asking a different way

[Luckyman01]

I have a crank no start condition.

I have tried replacing the Crankshaft position sensor and the fuel pump relay.

The cart will crank and start with the fuel pump relay jumped.

So the electricity is not getting through the relay.

Any clues on what info the relay is looking for prior to sending the power along?

David

[Beelzy]

Forget what I said. You already did it.

[obthomas]

You didn't say what year your car is but mine is a 2003 and the fuel relay switched contacts is powered from the fuse box in the drivers footwell. The ignition switch provides the fuel relay coil with power. The ECM in the trunk provides the fuel relay ground. When you jumped the relay you eliminated the fuse as a problem. You need to check the relay coil, if it is O.K. then the ignition switch power and then the ECM. Good Luck.

[JDMsurprise]

David, no one is fixing this for you, but you or your mechanic. This is a simple 4 pole relay that is super simple to diagnose. I know for a fact that the early cars (and as near as I can tell ALL 986 as I can best decipher from the wiring diagrams) are POSITIVE side switched. You have already tested the load side (the fat terminals by jumping those). Remove the fuel pump relay and get under the dash with a test light and poke around, you can literally do no harm. You are looking for constant ground and switched positive from the ECM. The switched positive might give you trouble, as you need to cycle the key. At least do yourself a favor and check this. Also, buy yourself a new fuel pump relay if the above test show you have power and ground on the the trigger side of the relay.

[Luckyman01]

A savvy fiend came by and we took a stab. We focused on the two fuel based relays. The fuel pump one up under the das and the one back in the trunk in right side.

To be honest I was barely keeping up and I will ask him to answer any technical questions.

Both relays passed bench test, clicked and functioned as expected.

However when a voltmeter was used, one pin measured 12 and the other 3.5 on the under the dash relay.

The back one seemed to get inconsistent signals from the magic box, TME, ECM ?

In fact when one turned off the ignition one side continued to show 12 volts when my friend believed it should drop to zero when the key is removed.


Anyhow I am not real technical of a guy. I can source the answer to clarifying questions.

While mu buddy when home and will think about it and come back, he is leaning towards a faulty DME as it seems to be sending incosistand signals to the DME relay in the trunk, I am clueless.

Does anyone know have a wiring diagram for the DME itself?

David

[JDMsurprise]

I think you are getting bad advice. The relay under the dash doesn't lose power on the load side when you remove the key. You need to verify circuit integrity on the trigger side of the under dash relay for signal and ground (separately). 3.5v on the trigger side may be caused by ECM pulsing the relay and delay in DVM (digital volt meter) reading. Don't expect 12v constant here until after the motor starts.

Sent from my SM-G781W using Tapatalk

[blue62]

what year is the car?

[Luckyman01]

2000 S Boxster

[Starter986]

Nevermind.

[blue62]

Luckyman,

Looking at the wiring diagram for the fuel pump relay you have four wires coming into the relay plugin.
They are labeled on the relay as..
30
85
86
87...

30 is the path to the fuse.... it is switched power to the relay.
when tested with a volt meter it only shows voltage with key on.

85 is ground at the ECU.. always shows ground key in key out... on or off.

86 is constant battery voltage..key in key out on or off.

87 is voltage supply to the fuel pump when the relay contacts close.

you know 30 and 87 are good because you jumped those and the car runs.

So test 86 and see if it shows constant battery voltage.
When you test 86 record the voltage reading you get.

also test 85 and see if you have constant ground.

Also test 30 and make sure you have voltage with the key on.
Record that voltage

Let us know the results.

Forget about the DME relay or other issues for now.
Chasing more then one issue at a time usually causes more problems then fixes.

[Luckyman01]

Long story short.

It was the fuel pressure regulator, there was a vacuum leak between this and the intake manifold.

Thanks to forum for responses and a subtle kick in the behind.

BTW, all the process, it appears that I have her in "Transport" mode now, likely due to tasking the battery.

DCM

[blue62]

Originally Posted by Luckyman01

Long story short.

It was the fuel pressure regulator, there was a vacuum leak between this and the intake manifold.

Thanks to forum for responses and a subtle kick in the behind.

BTW, all the process, it appears that I have her in "Transport" mode now, likely due to tasking the battery.

DCM

How did you track it down to a vacuum leak at fuel regulator???
What led you to looking there????

[Luckyman01]

I wish I could boast how smart I am, however I got there through a long path. I could get the car to run by jumping across the fuel pump relay.

My most recent work had been the fuel level sensor in the gas tank, so I thought I had done something wrong and took it out and checked the work there. Which in hindsight was not necessary ass the pump would work when the fuel pump relay was jumped.

Due to a lack of logic I starting throwing parts at anything I believed would impact fuel delivery.

I replaced the relays associated with fuel delivery and the crankshaft position sensor and the ignition switch to no avail.

Then I decided to check fuel pressure at the rail and went into the engine compartment, which brought up that a standard fitting on a fuel pressure gauge would not fit on the schrader valve on the right hand side of the rail.

That got me looking around the the fuel rail and I discovered that the elbow shaped hose
between the intake manifold amd the fuel pressure regulator was nor a tight fit.

I replaced it and all SEEMS to be well.

In short and in retrospect, I let pressure and anxiety impact the process.

While I have kept english and Italian sports cars on the road over the years, my mind does not seem as sharp as it once was.

David

I hope this issue is in the past.