RoadkingHI

My 97 S420 won't start. Good battery, good turn over, good spark. Appears fuel delivery is the problem but not sure where to check.
Note: Checked fuses and all good (in engine compartment and in trunk).

Suspect fuel oil pump but not sure where to check.

RichardM98

Did it happen all of sudden or were there starting issues which got worse until it wouldn't start?

RoadkingHI

All of a sudden, drove it two days before and no problem. The car is in excellent condition and well maintained so I am thinking a relay or pump failure. Will tackle it today.

RichardM98

The reason I asked was to rule out CPS which you just did.

RoadkingHI

I checked the fuel pump and it does not start when the ignition is turned on. I checked the plug to the pump and there is no voltage reading either.
I pulled out the relay and tested it. Put 12V to the two terminals and it pulled in the relay so that appears ok.
I am trying to trace further back and see what sends the signal to the relay.
I thought of hooking up a battery to the fuel pump and testing it but with no power to the connection plug I believe it is another modual or relay up the line.

RichardM98

Is there a fuse for the fuel pump?

RoadkingHI

Yep, fuse is good, and pump works when I use an external battery to test it. I am towing it in. Frustrated with all the electronics!!

RichardM98

Sorry for your troubles. It would help everyone if you would post the results at the dealer/indy.

TIA
Richard

mleskovar

CPS failure does not have to be intermittent. Is that what you're saying?

RichardM98

Anything can fail catastrophically. Especially electronic components. But most CPS's fail gradually producing cold starts followed by hot no-starts. I was just gathering clues in order to try to help OP.

mleskovar

Agree, but it's an easy start with a high failure part when you're guessing.

vettdvr

When you turn the ignition on the fuel pump will energize for a few seconds, if the CPS doesn't send a signal to the PCM to indicate the engine is running the fuel pump will turn off. This means to check power to the fuel pump you must do it when you turn the key on and watch on a analog meter or digital that will capture peak voltage. The power to the pump will be very quick on then off if the engine fails to start.

So this could still be the CPS failure as even if the engine is turning over a failed CPS would give no voltage to the pump and the engine will not start due to fuel turned off AND no spark.

RoadkingHI

Took it in and got a call back. For some reason the security system shutdown the signal to the pump.
What is confusing is the digital key has not worked for some time (I kept putting off fixing it) and doesn't have a battery in it.
The key has been used to open/lock the car and normal use. I am taking the valet key to the tech tomorrow to see if that has something to do with the alarm system. I doubt it but will find out. Ah, my '28 will for sure out last this, and the other newer, cars.

vettdvr

Breaker points don't have a security key.

RoadkingHI

Darndest thing. The regular, valet, key was put in the ignition and the engine started right up!
On the computer with the remote key in it shows all fine EXCEPT engine start was not permitted....
I am not an electronic wizard and I did not see this on any electrical drawings but only thing we figured out the key may be worn down some and there must be a pin/switch in the ignition switch that this key will not activate. Where as the other key, seldom used, triggered this contact/switch/sensor or what ever device tells the computer system to allow start up.
Thanks for the comments, checks and answers....

Makes you wonder if a car company just made a simple car, minimum extras (maybe radio and lights, ok throw in electric windows) it would probably sell and may last!

vettdvr

The MB I now have will be my last also due to poor reliability, long service times/drives, and excessive expense to repair what should have not failed. My list is way too long to post on a car bought new.

Jud Chapin

Can't disagree.