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Discussion Starter #1
I have a cps on order to address a warm crank/no start (only happened a few times ) but also wanted to check the fuel pressure to check the state of the fuel pump and had some funny results. I am reading no pressure with the ignition on but as soon as I crank it jumps to 48 and holds there while the car runs. Should I be seeing pressure with the ignition "on" ? When i turn the engine off the pressure holds around 45 but I have not left the gauge on for long. Is this normal or any suggestions on further diagnosis ?
 

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Gasoline pump should come on for short time when you turn ignition to position 2 and than stays on during cranking and running.
Residual pressure should hold for few minutes.
You have I6 engine?
Those are rare, but hopefully owner of the same engine will come with more experience.
 

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I have a cps on order to address a warm crank/no start (only happened a few times ) but also wanted to check the fuel pressure to check the state of the fuel pump and had some funny results. I am reading no pressure with the ignition on but as soon as I crank it jumps to 48 and holds there while the car runs. Should I be seeing pressure with the ignition "on" ? When i turn the engine off the pressure holds around 45 but I have not left the gauge on for long. Is this normal or any suggestions on further diagnosis ?
Residual pressure should hold for at least 30 minutes. If it drops rapidly check valve in fuel pump is stuck. If it drops slowly pressure regulator may be bleeding. Take vent line off pressure regulator and check for presence of fuel.
 

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Discussion Starter #5
Rechecked pressure after driving the car to warm and it's 48 psi at idle, when i unplug the vacuum on the fuel pressure regulator it jumps to about 54 PSI without any leaking fuel. Pressure holds after i turn off the car for at least 20 minutes. The ONLY thing that seems off is the fuel pump DOES NOT pressurize with the ignition on(cycled the key multiple times) the only thing I can assume is this model doesn't pressure fully with the ignition on, waits to pressurize until the engine cranks ? Instead of chasing further I just ordered a new cps, fuel pump, filter and relay and will replace. This is a car my kid uses away at school about 100 miles away the $150 in parts will buy me some mental relief and at 22 years probably not that far away from failure.
 

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I understand your concern with your kid's car, as a reliable car is needed especially when at a distance.

If the car starts after the first crank when cold, and it is slow to lose pressure, in all likelihood, the check valve in the pump and the pump pressure is fine. Your real complaint seems to be that the car does not start immediately after cranking on a warm start. While a CPS could be the problem, it is also possible you have leaky injectors. If this is the case, the cylinders get soaked with fuel which can cause starting issues.

I am wondering how you end up spending $150 on a fuel pump, filter, cps plus relay? The fuel pump relay is not separate from the K40 relay module, and it alone costs about $100.
 

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Discussion Starter #7
I assumed the relay was separate but you are correct. I saw some postings indicating the 97 had a relay on a board near the battery but just confirmed my car does not. Regardless I'm pretty sure the real problem is the cps but will also replace fuel pump and filter as well. My fuel pressure test indicates pressure holds after shutting off the engine.
 

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Discussion Starter #8
I am still not sure about the zero pressure with the key in position 2 with the car not running.I have cycled the key a few times and no pressure before cranking. Is this normal ? It does reach 48 psi as soon as I crank.
 

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Was the car used when you purchased it ? If so, is it possible that someone butchered the fuel pump relay circuit ?
 

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dho:

My experience with Crank Postition Sensor failure is that once it fails, it doesn't come back, engine will crank forever & not start.

It happed to our m112 in our e320 wagon on a hot August day last summer. I supected it, told the wife to leave it parked until evening cooled fully. (12 miles from home hoping to avoid a tow)

So we started it up & immediately drove home. Once in driveway, it wouldn't restart under ANY conditions. PTL, made it home & no tow.

My son with skinny hands did the CPS replacement; hasn't missed a crank / start since that day.

On this car & M113 V-8 in the ML they both show pressure immedately upon key in position 2.

Doesn't the early w210's like yours have a slighly different fuel injection system & maybe it operates differently in that respect - I mean your engine is starting fine & shows good pressure.

Pardon if you've covered this but did you do Fuel Filter ?

Cheers David
 

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Discussion Starter #11
I purchased it used but know the original owner well and it's never been molested. It is a inline 6 and I don't know if the fuel pump pressuring is a bit different than the v6 used in later W210 series. Fuel pressure holds for at least 30 minutes after turning the car off so I'm assuming the injectors aren't leaking. My year still uses the switch blade key so there's that whole weirdness.
 

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I believe in your case the fuel pump only works if the ECU (engine computer) sees a valid rpm from the CPS. This is different from the V6 because fuel supply methods are different.

If the car cranks and starts well when the engine is cold, then no need to worry when the fuel pump is turned on.

You can replace the fuel pump if you like, and it is a good preventive maintenance item due to age, but it may not solve your problem. If the pump delivers a liter of fuel in 35 seconds, it should be good. You can test it using the return line of the fuel rail.
 

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Discussion Starter #13
Thanks for the clarification, it makes sense about the lack of pressure. I'm pretty certain the no start was CPS related since my magic wiggle did the trick. The only other simple/logical thing would be a flooded plugs from leaky injectors(multiples) and my pressure check would lead me to believe they are not leaking. I might be being a bit neurotic about the fuel pump but at this point the cost of the pump and filter will be nothing compared to the wrath of mom if it strands my kid because the fuel pump decides to die in the next 6-12 months especially with a 22 year old fuel pump. If this was my DD I would do nothing until it became more of an issue but the thought of getting a call at 2 am isn't worth the additional $100 and a couple hours in the evening.
 

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As long as you replace it with OE or a good brand pump, that is fine. But many go for the cheap Chinese stuff which ends up going bad sooner than the original one, if left in place.
 
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