Bizarre misfire
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Bizarre misfire
I've had a 97 Ranger for a couple months now. 2.3 engine,manual,145k miles. It has a bad,regular(not random) misfire when its cold. When the engine is fully hot the misfire completely goes away at idle.However if I rev the engine and quickly take my foot off accelerator and let it quickly return to idle the misfire is back. At that time the fuel trim numbers shoot up to a lean condition.If I let it idle a few moments the misfire once again goes away and fuel trim numbers return to normal. Things I've done to it so far: new CPK sensor,4 new fuel injectors,8 new plugs and wires,1 new coil(swapped to check),replaced plenum and EGR gaskets,piston soaked 2 of the cylinders. Not sure what could be "changing" when going from high rpm to low rpm to make it misfire. I thought maybe oil could be coming up around the cylinder rings and soaking the plugs on that cylinder at high rpms,then the oil clears at low rpm(idle) and the plugs again start firing on that cylinder. The wiring harness was in bad shape,wires stuck together,almost melted.I straightened all that up.I'm stumped on that misfire.Any ideas?
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From: SW Va
Welcome to FTE.
You've been busy on this puppy, post up All trouble code Numbers, as they can help focus a trouble shoot.
Were, or did all of those parts test bad, or were they in need of replacement, or did your scan tool flag cylinders on a power balance test, or were you just tossing parts at the problem & hoping for joy?
Where now is the vehicle on All past & present due scheduled maintenance replacement parts? Were the replacement parts installed so far the specified OEM design, or least expensive aftermarket?
At first glance it sorta sounds like it could be a gasket sealing problem, but at this point it's just a wag on my part, we need a lot more info like trouble code Numbers & some vehicle history for clues on where best to begin..Did the problem come about suddenly after some event, or slowly over time?
You've been busy on this puppy, post up All trouble code Numbers, as they can help focus a trouble shoot.
Were, or did all of those parts test bad, or were they in need of replacement, or did your scan tool flag cylinders on a power balance test, or were you just tossing parts at the problem & hoping for joy?
Where now is the vehicle on All past & present due scheduled maintenance replacement parts? Were the replacement parts installed so far the specified OEM design, or least expensive aftermarket?
At first glance it sorta sounds like it could be a gasket sealing problem, but at this point it's just a wag on my part, we need a lot more info like trouble code Numbers & some vehicle history for clues on where best to begin..Did the problem come about suddenly after some event, or slowly over time?
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No trouble codes.A couple of times a P0171 popped up but I can "manipulate" the RPMs and that code wont return after I clear it. I have a C reader 3001. All monitors set quickly on this truck.Yeah I basically been throwing parts at it.Some are not OEM but I don't think that's my problem. Bought it from a part-time dealer and he said he changed the IAC valve,it does look new. Thought it might be a weak valve spring,but that would not explain the misfire slowly going away at idle.Had the valve cover off,didn't see anything out of the ordinary. Compression is good,all cylinders between 178 and 183. Did a leakdown test and all 4 cylinders did not seem to be losing air at an alarming rate. Got a few more things I need to try,vacuum test,clean the other 2 cylinders,etc.
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From: SW Va
Ok good feedback on the P0171 code coming & going. That's a system too lean code & goes along with your observed fuel trim going lean.
SO, have you performed a fuel pressure & volume over time test, to see if the fuel pump & filter are able to man up to the task of providing enough fuel at the specified pressure?
With the mileage on this puppy the PCV valve is due for a change & seeing as how it's downstream of & thus it's calculated for vacuum leak operation not being monitored by the MAF sensor, any acting out of the PCV valve from being mucked up & sticking, or its spring being wimpy from wear, or its seat being worn & leaking, its rubber hoses dry-rotted/cracked, all amount to a uncontrolled vacuum leak ....well you get the idea, any acting out, or connecting rubber hose or grommet leaking air can corrupt fuel trim. So if what's causing it to act out is heat sensitive, like varnish, gum, sludge, or carbon deposits, cracked hose, or loose fitting grommet, its problems can come & go!!!!
SO, have you performed a fuel pressure & volume over time test, to see if the fuel pump & filter are able to man up to the task of providing enough fuel at the specified pressure?
With the mileage on this puppy the PCV valve is due for a change & seeing as how it's downstream of & thus it's calculated for vacuum leak operation not being monitored by the MAF sensor, any acting out of the PCV valve from being mucked up & sticking, or its spring being wimpy from wear, or its seat being worn & leaking, its rubber hoses dry-rotted/cracked, all amount to a uncontrolled vacuum leak ....well you get the idea, any acting out, or connecting rubber hose or grommet leaking air can corrupt fuel trim. So if what's causing it to act out is heat sensitive, like varnish, gum, sludge, or carbon deposits, cracked hose, or loose fitting grommet, its problems can come & go!!!!
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Joined: Feb 2002
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From: Tucson USA
I had similar issue on my 94 4.0. Had a miss that I just could not find, new wires, plugs, coil pac, the box on the radiator frame all of it. Took it to a shop and they tried to find out what it was, said all work done was good and they were also stumped. Said the injectors were OK. At any rate I just went and changed the injectors and that took care of it. Guess that the ok meant they were working but that was about it. Not saying this is your problem but not all misfires come from the ignition system. from what I have read the injectors have a life of around 150000 miles in most vehicles. I am sure there are exceptions. On mine I had them cleaned at a shop and that was at 150K or so, and when I changed them they were around 300000. had same type issue with an old F250 I had, miss and everything, had to change the injectors on it also.
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New PCV valve.Fuel pressure stays around 40 psi. I'm almost certain its one particular cylinder causing the problem.A bad MAF or low fuel pressure wouldn't "pick on" one particular cylinder.Still working on removing carbon from cylinders.Like I say,if I let it idle after engine is fully hot misfire goes away,but then I rev it to 2000 RPM for a few seconds,jerk my foot off accelerator pedal and let it return to idle the misfire is back! Sounds like an IAC problem but like I say the IAC looks new,and anyway it would not "pick on" one cylinder. I'm leaning toward oil slinging- fouling-clearing at this point. But compression is strong so I think the rings are in good shape.Strange.
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Fuel injectors are all new.Gonna buy a stethoscope to listen to them anyway.Also gonna buy a vacuum gauge. Maybe one of the wires to an injector is acting up.Like I mentioned the wiring loom was in VERY bad shape,lots of melted goo in there.
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Fiddled with it some more today.Noticed something interesting,not sure if it relates to the problem though. When I pull both #1 plug wires off at the coil a strong spark makes its way down the post and to the top of the coil.On both coils.One coil is new. It does not do that on any of the other plug/coil wires. No spark is visable though when plug wires are pushed down on post. Is that normal? I would think not. Pulled 4 plugs as well,(passenger side). Looks to be a small amount of oil fouling going on. I fear that be my problem.But if it was slinging that much oil you would think there would be white smoke from the tailpipe,I don't have that.
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From: SW Va
Not good practice to disconnect the plug wires with the engine running & let it arc like that. It'll over voltage & electrically over stress the coil pack insulation & cause carbon tracking where it arced & that can cause electrical leakage along the carbon track, all a vicious circle that can come back to aggrivate at the most inopportune time.
To safely check for spark, use your inductive timing light.
On the 4banger with dual coil packs, only the coil pack feeding the exhaust manifold side spark plugs are used to make spark on a start, so only that coil pack is activated on a start.
Have a read here on your ignition system basic operation & how to trouble shoot it https://easyautodiagnostics.com/ford...sensor-tests-1.
To safely check for spark, use your inductive timing light.
On the 4banger with dual coil packs, only the coil pack feeding the exhaust manifold side spark plugs are used to make spark on a start, so only that coil pack is activated on a start.
Have a read here on your ignition system basic operation & how to trouble shoot it https://easyautodiagnostics.com/ford...sensor-tests-1.
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Not a ton,but some. Don't know what else it could be. The misfire goes away after setting at idle for 5 minutes,but returns when I start revving the engine. And is always there while driving down the road. Its a regular miss and I'm 99% certain its the same cylinder.What else would slowly "resolve" while setting at idle?
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From: SW Va
Not a ton,but some. Don't know what else it could be. The misfire goes away after setting at idle for 5 minutes,but returns when I start revving the engine. And is always there while driving down the road. Its a regular miss and I'm 99% certain its the same cylinder.What else would slowly "resolve" while setting at idle?
OBD-2 is rather sophisticated, so not likely missing a regular occurring event like that kind of problem.
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If you have a regular miss idling, or going down the road, OBD-2 will detect a cylinder misfire. On a regular occurring misfire the CEL will be blinking & the computer will store a code for the acting out cylinder.
OBD-2 is rather sophisticated, so not likely missing a regular occurring event like that kind of problem.
OBD-2 is rather sophisticated, so not likely missing a regular occurring event like that kind of problem.
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From: SW Va
Yup it's OBD-2, everything 96 up had to be. Change was begun in 95. Some late 94 & 95 vehicles were OBD-2 & everything had to be OBD-2 in 96 & newer. Does your CEL light up for its self check at KOEO, before you crank the engine?