mystery miss
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mystery miss
Heres the scenario, 93 aero with 4.0, picked up a very harsh miss a couple of weeks ago, seemed to be worse when warm and when there is a load on it such as going up a hill. It was a very harsh miss like turning of one cylinder and then back on. My first thought was to change plugs and wires. Went down to the local auto parts store and purchased motorcraft plugs. I was very glad to see it had autolites in it, never had good service out of autolite in anything except they do make good fishing sinkers, lol, anyway replaced the plugs finding 3 very clean, 2 slightly brown and 1 with a brown crust on it, I'm thinking ok well that should solve the problem. Engine starts right away has a very slight miss at idle, but when I drive you can definetly tell it running on 5 cylinders only its not jumping like before, and yes the warmer it gets the worse it is, what do you think? Should I try the wires next?
Thanks
Thanks
Post Fiend
Joined: Apr 2005
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From: Washington state
clean MAF heated element first....pull 2 torx screws and remove element
soak in a shot glass full of TB cleaner for an hour....
examine with magnifing lens....any dirt or crud remaining=replace with new
correct MAF voltage should be approx 0.8v at idle air flow and approx 2.5v at 2,500 rpm
put in new air filter and check filter box plus black tube fittings for any air leaks....change PCV...dirty old worn out thinned down engine oil can cause MAF contamination from PCV overload....also the aftermarket cotton diaper air filters are notorious for leaking thru dirt and dumping overoiled crud onto MAF element....stick with the factory air cleaner, will flow twice what a 4L requires at 6k rpm
check your auto tranny vacuum modulator vac. line for ATF leak thru from failed diaphram...back sprays thru plenum and TB, can contaminate MAF...also overloads crankcase with ATF volitiles which go thru PCV and goo up the MAF
i have to clean my MAF every couple years, more if dusty logging roads or desert trips...
original factory OEM MAF 170k miles and still going strong
soak in a shot glass full of TB cleaner for an hour....
examine with magnifing lens....any dirt or crud remaining=replace with new
correct MAF voltage should be approx 0.8v at idle air flow and approx 2.5v at 2,500 rpm
put in new air filter and check filter box plus black tube fittings for any air leaks....change PCV...dirty old worn out thinned down engine oil can cause MAF contamination from PCV overload....also the aftermarket cotton diaper air filters are notorious for leaking thru dirt and dumping overoiled crud onto MAF element....stick with the factory air cleaner, will flow twice what a 4L requires at 6k rpm
check your auto tranny vacuum modulator vac. line for ATF leak thru from failed diaphram...back sprays thru plenum and TB, can contaminate MAF...also overloads crankcase with ATF volitiles which go thru PCV and goo up the MAF
i have to clean my MAF every couple years, more if dusty logging roads or desert trips...
original factory OEM MAF 170k miles and still going strong
Last edited by 96_4wdr; May 7, 2007 at 10:43 PM.
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Joined: Jun 2006
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From: Newmwnstown, PA
I definitely agree with 96_4WDR. I cleaned my MAF as he described for the first time just over 200K miles and my '93 3.0L Aero runs very smoothly now with 205K miles on the OEM MAF. My MPG has climbed from 17 to nearly 24 MPG (yes, I also changed the OEM O2 sensor and IAC at the same time). I do get a low voltage reading during the OBDI diagnostics, but the CEL doesn't light up and my MPG is GREAT! Should I leave well enough alone or just go ahead and replace my MAF?
Michael
'93 Aero 3.0L EXT (205,453 miles)
Michael
'93 Aero 3.0L EXT (205,453 miles)
Elder User
Joined: Dec 2006
Posts: 830
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From: Kitchener,Ontario,Canada
Originally Posted by weedhopper
code was 157, maf low voltage, do you think the miss could be caused by a bad maf? I did have that problem on a n escort and a new maf solved the problem
Sounds like the element is becoming suspect, this sensor is one of the key sensors in getting correct fuel mixture into the engine. With a carb engine you could play with the jets, cant do that with an ECU. Definately try the cleaning trick.
I just checked my MAFV readings & I dont get any voltage belw 0.97 volts at idle , around 850 RPM's. Mine idles with no problems.
A misfire like this could be a sign of injector blockage or leaking, since you did not have a black spark plug you might have a gummed up injector,which could run lean. Have you replaced your fuel filter lately? Were the clean plugs all one one bank of the engine? If the codes dont tell of the misfire you could do the plug wire pulling trick at idle, although I believe that with OBD1 there is a misfire testing mode which simulates the old plug pulling trick & measures engine RPM drop while disabling one plug firing at a time..
ATB Aeroman
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From: Kitchener,Ontario,Canada
Originally Posted by LTCPipkin
I definitely agree with 96_4WDR. I cleaned my MAF as he described for the first time just over 200K miles and my '93 3.0L Aero runs very smoothly now with 205K miles on the OEM MAF. My MPG has climbed from 17 to nearly 24 MPG (yes, I also changed the OEM O2 sensor and IAC at the same time). I do get a low voltage reading during the OBDI diagnostics, but the CEL doesn't light up and my MPG is GREAT! Should I leave well enough alone or just go ahead and replace my MAF?
Michael
'93 Aero 3.0L EXT (205,453 miles)
Michael
'93 Aero 3.0L EXT (205,453 miles)
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I cleaned as described, then cleared the codes ran engine till warm up was complete then drove about 5 miles, Seemed to run fine other then while on the test ride the muffler blew out, I replace that tomorrow and also recheck the codes to see if 157 came back. I'll let you know. Thanks for the help.
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From: Kitchener,Ontario,Canada
Originally Posted by weedhopper
I cleaned as described, then cleared the codes ran engine till warm up was complete then drove about 5 miles, Seemed to run fine other then while on the test ride the muffler blew out, I replace that tomorrow and also recheck the codes to see if 157 came back. I'll let you know. Thanks for the help.
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Ok replace the exhaust now its very quite, miss did not go away the 157 code did not come back, replaced the plug wires and now she runs fine, I've put about 20 miles on it and so far so go. Thanks for the help. If anything changes I'll let you know.
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