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  #1  
Old 01-25-2007, 08:59 AM
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Join Date: Apr 2005
Posts: 136
Need opinion on fuel injector replacement

Hi guys,

I just need your experience on this idling issue I have. It's more a slight shake than a stumble. As you might have guessed I replaced 1 steel injector that fouled up when I previously had a burnt valve with a brand new brass kind.

When mixing old(steel) and new(brass) injectors, is the opening pressure difference great enough to cause irregular idling? I'm thinking that since the entire injection system has the same pressure from distributor to injectors, new injectors mixed in with the old actually causes fuel starvation for its assigned cylinder.

My issue is there at start-up then goes away during warm-up, but comes back at WOT. Vacuum lines have been checked and replaced those that needed it. Ignition parts checked/replaced. Air/fuel mixture at 50% with a new O2 sensor.

Thanks in advance.

bpaz_ph
'87 190E 2.3 8V

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  #2  
Old 01-25-2007, 02:35 PM
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Join Date: Aug 2006
Posts: 141
Miss at idle

Have you determined which cylinder is hitting light? Break loose injector lines at the fuel dist. one at a time and look for the one that the least RPM drop. Next swap the injector from the weak cylinder to another hole and test again. If the miss moves with the injector replace it, If not look for compression,ignition or fuel dist. problems at that cylinder.
Good luck Mike
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  #3  
Old 01-26-2007, 04:16 PM
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Mike,

Thanks for replying. How do you break the line while the engine is running without making a mess? Just the idea of 3bars of 93 octane spraying allover the engine frightens me.
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  #4  
Old 01-26-2007, 07:36 PM
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Join Date: Dec 2004
Location: Eugene, OR, USA
Posts: 121
uneven idle

The idle on my '86 300E smoothed out a lot when I replaced the injector seals. I identified the seals as leaking by spraying carb cleaner on each seal and listening for any change in the idle. If the idle changes, you know the carb cleanr is being sucked in around the seal.

My old seals were so hard they shattered like glass when I removed them. The new seals were nice and soft and inexpensive too. This isn't a hard job to do at all.
__________________
1986 300E
1993 Volvo 940 Wagon
1984 Volvo 240 (daughter's)
1976 Dodge 1/2T pickup, gas hog
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  #5  
Old 01-27-2007, 05:30 PM
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Join Date: Jan 2007
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you don't open the line while the engine is running, rather you let the engine run for a while till the pressure on the line has increase (say around 5 minutes in idling speed), then shut the engine and start with each line (top fo the the fuel distributor) slowly opening each line and see if there is pressure and fuel coming out from each line
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  #6  
Old 02-01-2007, 03:05 PM
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Join Date: Apr 2005
Posts: 136
Thanks for the replies.

I'll check the seals this weekend.

As for disconnecting the lines, I think this would be a good test for injector leaks. One question though, does each fuel line hold its own pressure? I mean if 1 injector is leaking (meaning pressure drop on this line) would the other non-leaking injectors maintain their pressure?
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  #7  
Old 02-08-2007, 08:36 AM
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Join Date: Apr 2005
Posts: 136
Thanks again.

It was definitely an injector seal problem. The new injector had a shorter seal and since the old seals were stiff, it didn't let the metal brackett go all the way down to seal the new one.

Engine performance is now at acceptable level, enough for me to move on to other issues.

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