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09-20-2022, 08:43 PM #1Member
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Lean sneeze Mercury 3.0 HELP Pls - 1998 250 efi
Looking for some help on a 1998 250 efi. It has a lean sneeze at idle and I don’t know what else too look for. The sneeze actually blew one of the new bleed lines in half. It’ll idle then start sneezing. Here’s what I’ve done
New TPS set to .98
new map sensor
new air temp sensor
tested temp sensor - ok
new bleed lines- correct brand
checked each and every check valve in bleed system…replaced as necessary
inspected reeds…original but intact nothing broken
fuel pressure at idle is 39 psi
plugs are newer ( low hours)
compression 90 in all cylds
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09-20-2022, 09:16 PM #2
You might want to have the fuel injectors cleaned & flow tested... sometimes they stop spraying the fan/cone mist and just piss a stream of fuel that won't atomize at idle?
Let's just go ahead and make America great again!
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09-20-2022, 10:53 PM #3
1998 .. the reeds might look fine, but the rubber they seat against is usually dry and cracked .. You have to either lift each one with a finger nail and shine a light and see what ya got. Or fill the block with safety clean .. to see if it leaks. Chris Carson has a fix for it .. He surfaces the blocks and sells an oversize fiber reed ...
I wont even use a new block with the rubber still on it ..
The correct bleed line is .. buy a roll of 1/8" fuel injection hose from NAPA .. The part number is either HP 74 or HP 174 .. (its late) It might even have the HP after the number ..
It's identical to what the late model 3.0L use ..
Small tie wrap at each end .. you won't have to worry about them again ..
As stated .. get your injectors flowed / cleaned.
When they are cold .. I like to lift the cowl and give em a squirt of gas .. I hate it when they sound like a horse sneezin ...
Buuuddddaaaa-Ka-CHOOFfff-bummmbbudabumm ....
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09-20-2022, 11:19 PM #4
I like these little radius-end zippies for hoses & cables: https://www.nelcoproducts.com/store/...-zip-ties.html
Let's just go ahead and make America great again!
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pcrussell50 thanked for this postpcrussell50 liked this post
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09-21-2022, 05:41 AM #5Member
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Should have mentioned…injectors were cleaned and tested last year…
I’ll pull the reed plate. I wanted confirmation the reeds could be the issue before I did that and you gave it to me. I’ll call Chris Carson and start with new reeds. Thanks again
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David - WI liked this post
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09-21-2022, 07:57 AM #6
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09-21-2022, 08:09 AM #7
I have the same issue with my 3.0, hopefully it's the reads and I dont have to go through all the troubleshooting you have in your list...How easy is it to get at the reeds taking all the EFI stuff off ?
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09-21-2022, 11:58 AM #8Member
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getting to the reeds wasn't bad. Lots of allen bolts on the front cover (the 2 bottom are blocked by the cowl so they took some time). After that 3 bolts and 2 fuel hoses for the VST, 2 bolts for the fuel separator, and disconnect the oil arm (pops off) and you have access to the reed plate. I did it in about an hour or less.
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09-22-2022, 07:16 AM #9Member
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Inspected the reeds and they are 100% perfect. I'll obviously replace them at this point but any other suggestions on the possible cause of the lean sneeze? I'll inspect the injectors next even though they were cleaned / tested last year. Could it be a failed injector?? Any easy way to test for that?
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09-22-2022, 09:40 AM #10
It's not the reeds themselves, but the rubber base they seat against.
That thin bleed hose will blow off the barb behind the electric's plate and oil bag.
They had some years where the routing did some crazy things. Simple is best ..
Front half to block : top to bottom / middle to top / bottom to middle.
The little guy on the lower counterweight housing might not be drilled and tapped (usually just 300x and 300xs) #13-14 but it goes to #6 cylinder. It will lube the #6 cylinder as it vacuums out the housing. All those other checks and hoses just need to be closed off with 1/16" npt plugs. By the time they figured it out .. they quit making the *&%%&*8 things ..
Doesn't show it here, but don't forget the oiler from the base of the front half to the top bearing area. Outgoing check at the bottom / open fitting at the top ..
Use the hose from NAPA ..
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09-22-2022, 09:50 AM #11
Take your injectors to a diesel shop or a shop that does Hi-po imports. (white and pinks are Keihn, which is owned by Honda) They should have a cleaning flow machine .. make friends and they will do them in front of you while you wait ..
The injector clinic is aprox 20 miles from me. I got tired of driving 40 miles to get them done .. or 80 miles if I had to drop them off and come back .. so I bought my own machine ... LOL
If ya need one or two, I have plenty of white, pink and pencil injectors in my stash. Let me know what your known good ones flow , I guess I could let one go ..
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09-22-2022, 09:57 AM #12
That motor has a tapered crankshaft with a keyway. I'd check to see if it sheared and the flywheel is out of time. hf...
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09-23-2022, 09:28 AM #13
I've not really seen the 3.0L to be known to shear the key .. but worth checking. As is the air gap on the crank rigger eye. .040 - .050 ...
I still go back to vacuum leaks as the number one cause of the big Kaa-Chooffff ..
I was helping my neighbor fix his sons little Yamaha. The wife comes out and asks : Did you find the problem. No ma'am, but we can tell you all the things it's not.
When we put the kit in the carb, we found that two of the four holes that the idle fuel is added progressively at tip-in, were clogged. Symptom was, if you turn the throttle up slow .. it would die. Zoom-zoom now ..
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10-07-2022, 11:22 AM #14Member
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UPDATE: Installed new reeds and the motor lean sneeze is gone. It idles much smoother and noticeable acceleration smoothness. Its smokes excessively now and fouls the plugs. I did notice one thing which I'll start in a separate thread. The bleed return line on the VST is cut and blocked off. I have the manual but can't see anywhere where it shows where this line should go. I see a reference to in the 1997 EFI diagram but doesn't seem to be the same as 1997 and newer. Another step forward but still not fixed.
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10-07-2022, 11:35 AM #15
All the fuel from the high-pressure pump goes to the fuel rail. From there it is returned to the VST tank. The little chrome-dome guy held down by two screws is the pressure regulator. There is a hose barb/ port that leads to the base of the regulator. Install your return line there.
Clean the little screen under the regulator, as it will restrict flow. Personally, I throw the little POS away. Because I have a screw on filter at the tank, another one on the VST, the hi-press pump has one on the bottom and each injector has a little filter basket. Just how many filters does one man really need ...
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