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Old 01-29-2002, 03:49 PM
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Angry worsening vapor lock - going to vomit now!

I have been fighting with this car for so long now, that I am about to vomit. And I am against that.

I am a pretty good back yard mechanic, but can't figure this out. When the car sits for more than a few seconds, after switching off, it takes several seconds to re-start.

If it sits for about twenty minutes, it takes about twenty seconds to start. Ironically, if it sits overnight or longer, it usually only takes about five seconds to start. If this were any other car, I'd call it "vapor lock."

Usually, after several seconds on the starter it fires on 1 cylinder, then 2,4, and with a rev or two, all is OK...

I have checked most of the mechanical and electronics on the Bosch syste, but I must have missed something. So did my local mechanic. After about three hours on the job, including a fuel pressure test, he handed me back my keys and said that I should go to a Mercedes specialist.

I admit that I felt better that the problem stumped him, too, but still I just want it fixed...

I have checked the accummulator, regulator and individual injectors for leaks, including the cold start injector. All seem good.

Please volley your guesses my way. I'll try anything.

Any chance it's not fuel related, and I am barking up the wrong tree?
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Old 01-29-2002, 04:01 PM
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my guess - fuel pressure. I have a winter beater car Olds V8. Let it sit for up to 3 hours - starts instantly. Let it sit longer - cranks many many times to build up pressure then fires instantly. In my case pressure is being lost over time - ain't worth troubleshooting - as long as it runs! Suggest you check fuel pressure - if it not there it won't start. The longer you leave it the worse it gets - right? If your pressure regulator isn't doing it's job - that could be it. One crazy thought - do you have an electric fuel pump? Is it putting out enough pressure? (most likely). However - on my Mercedes V8 I have 2 electric fuel pumps - and there is a CHECK VALVE screwed into the output side of them. If you have such a valve on your electric pump and it is not holding pressure----TA DA!!
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Old 01-29-2002, 04:08 PM
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Thanks for the reply. In this car, there are two fuel pumps (87 260E) and two check valves all in series. I'm not sure why two pumps would be necessary, but maybe one is not functioning right...

I have replaced both check valves, but it did no good. Honestly, the odds of both failing was pretty slim...

Interestingly, the problem is intermittent - at least it has been. Some times it would start right up, but lately, it never starts right back up.

If it sits long enough like 24-plus hours, it will usually start up pretty quickly...

It's just killing my battery, and probably my starter to keep things going like this.

Appreciate your
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Old 01-29-2002, 04:20 PM
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Hi Steve
Check the pressure at the regulator and see if it is there. Is there any chance there is a little crud in the check valves that could allow some seepage back? Apparently they need the two pumps in series to provide the pressure required. Two last things I can suggest.
1) turn the key on and listen for the electric pumps to cut in -when they reach proper pressure they will shut off. THEN try to start the car.
2) Take you two pumps in and have them checked for volume and pressure output.

I have a feeling that your problem will be somewhere in the circuit between the pumps and the regulator.
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Old 01-29-2002, 04:21 PM
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One other stupid thought - if you had the check valves out - can you blow through them one way but not the other??? Can they have been put in backwards???
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Old 01-30-2002, 02:15 AM
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At first it sounds like an accumulator or check valve problem, but since you've ruled that out...

Wild speculative guess: Fuel pump relay. I had a similar problem on a 107 traceable to the pump relay - it would supply voltage intermittently while cranking.

Even if you have voltage and hear the pumps run when you first turn the key to the 'run' position, it is not assurance that you are getting *consistent* voltage to the pumps when actually *cranking* - at least on earlier cars, the voltage is supplied by different circuits (terminal 30 & terminal 15 if I remember correctly)

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Old 01-30-2002, 05:32 PM
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Steve - is this the same situation reported back in Oct. of last year?

Fuel Injection diagnostic 103 engine. Need advice.

Did you check the fuel pump relay as suggested by one of the contributors in that thread?
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Old 02-01-2002, 09:44 AM
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Yeah, same problem as forever, just worsening. The accumulator tested OK, with no leaks, so I am still searching for the solution.
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Old 02-01-2002, 01:37 PM
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Hey Steve - just asking - are you sure BOTH fuel pumps are working properly? You probably have but I always find that on car problems that are perplexing - the cure is something that we end up saying "Ya gotta be kiddin". To follow through:
1) fuel pumps engaging and putting out proper pressure.
2) check valves good and holding pressure
3) accumulator holding proper pressure
4)regulator properly set and working
5) injectors are good and not leaking
6) cold start injector working
If all these are met - the car should start instantly. If you know 1-5 are for sure good - that leaves maybe #6
How did you check you cold injector? If the 5th injector does not spray enough fuel in - the car will be hard starting as you describe. Did you also check the circuitry to the 5th injector? Sensors - relays?? One crazy thought - if you pull the fifth injector and put it into a jar and have someone crank the engine and see what you get out while it cranks. If you haven't tried this - I bet you will get very little or nothing coming out of the 5th injector and the car will start as enough fuel comes in from the other injectors over a few seconds.
Just a thought - I sympathize with you because I am too am a DIYer and am the same way with my Benz - if it was designed to run right - it should - and I will continue to bombard the problem til I find it. As I said above - follow the check list - something HAS to be measuring wrong - or it would work.
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