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Old 09-04-2009, 09:16 PM   #1 (permalink)
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rough idles - stumbling after new fuel pump

So the new fuel pump took care of the problem of the car not starting when it was cooler out but would start when it was warm out.

But now it idles a little rough. It doesn't seem to have as stong of acceleration either. It runs OK while accelerating but while coasting it stumbles and runs a little rough. Thought I heard a bit of ping and maybe a little backfire today. The car actually ran better when I had the old pump in (when it would actually start).

I went to a local parts place and they loaned me a fuel pressure guage. I checked the pressure as instructed in the Bentley Manual and it read about 47 PSI (Bentley manual says it should be about 43.5 PSI. I pulled out the fuel filter (which was replaced when I put in the new pump). I had someone crank the engine while I had the fuel line off the filter and it filled a glass jar with no problems.

So rough idle usually means poor fuel/air mixture - so could it be the fuel pressure regulator mounted near the fuel rail?

I also added some injector cleaner in the tank today too.

I also pulled the air filter hose (it has a new air filter) and sprayed carb cleaner in to the intake to see if something was gummed up.

Any other idea's or thoughts on the pressure regulator?

Thanks!
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Old 09-04-2009, 11:09 PM   #2 (permalink)
OMFG another one!?
 
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How's the fuel filter? Maybe the change of the pump stirred up some tank dirt.
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Old 09-04-2009, 11:53 PM   #3 (permalink)
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Today I pulled the filter out and blew thru it - no crud in it at all (I replaced it when I put the new pump in a few weeks ago). I ran the pump before putting the filter back on today just to see if there was anything in the line.
The only thing I have not done was pull the line off at the fuel rail to check fuel rate of delivery (after the regulator). I might do that sometime this weekend.

I'm giving in and taking it to a shop here in town on Wednesday that specializes in European cars.
Seems like everytime I fix something, another problem pops up - I'm getting a bit frustrated to say the least.
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Old 09-05-2009, 12:07 AM   #4 (permalink)
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Could there be some leakage in the fuel line?
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Old 09-05-2009, 12:42 AM   #5 (permalink)
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After I replaced pump and filter - I checked for leaks, I left cover plate off of fuel pump access hatch for a while just to be sure. I also don't see any leaks at fuel rail.
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Old 09-07-2009, 07:42 AM   #6 (permalink)
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most likely its has nothing to do with fuel or pressure.

it sounds like vacuum leaks or gaskets. older car with great motor. i am looking for one. do you have any ses lites or codes? check sensors. start simple. vacuum leaks, hoses all connected, sensors all connected and working.

read the code.
search the internet or forums

love the car. auto or man?
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Old 09-07-2009, 12:55 PM   #7 (permalink)
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Thanks for the reply rajk9800.
It is an Automatic.

I have been searching for vacuum leaks the last few days and did not find any.
I also checked for codes but I didn't get any trouble codes.

But I did find the problem and it is running fine now. I posted another thread but here's what happened. . .

The same day I replaced fuel pump, I also replaced crank position sensor. To provide more access to it, I moved the distributor cap out of the way. In doing so, I loosened two of the wires going to it.
Yesterday I was checking plugs to look for fouled plugs because I noticed a gas smell in the exhaust which to me means a cylinder isn't firing and I'm pushing raw gas out the exhaust.
As I was checking, I decided to push down on the wires to the distibutor and two of them were not seated all the way. I also replaced the plugs becasue I know from the previous owner they had been in for 4 years. They also put in platinum tip plugs and I thought I read something about it not being a good idea to use platinum plugs in these engines.

So it is running fine now. I still have a few more tasks to do - change tranny filter and replace the thrust arms.

Thanks again for the reply.
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Old 09-08-2009, 04:27 PM   #8 (permalink)
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I had the same prob. with my car. I replaced all the vaccume lines and also the coils. I put platinum plugs in at first but quickly realized that wouldnt work so I went with the cheap a/c delco plugs and the motor loved it. I also found a small leak in my radiator, a friend said it could have been overheating a little causing it to stutter. Now the car runs great.
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