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engine has a constant misfire and bogs at wot
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zinnoberot
Novice
Jan 14, 2010, 2:04 PM
Post #1 of 13
(3460 views)
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engine has a constant misfire and bogs at wot
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Hello I have had this problem for four years. The car is a 1986 bmw 325es with a 2.7L engine. The problem I have is a constant misfire or appears to be a misfire at 2800-3200 hot or cold but once I pass those rpms if I open it wot it bogs terribly but if I feather the throttle I can rev to 5k and it pulls like it should but it wont allow me to go wot. Also I watched the exhaust one night in the side rear view mirror and when it misfired I seen it in the exhaust stream. It was cold out so I could see the moisture coming out of the exhaust but right when the car misfires it had no moisture in a few strokes what i would be assuming an injector not firing or no spark. Now the list the stuff I have changed or swapped with a known normal running car.
ecu-swapped no change
afm-swapped no change
tps-swapped no change
new fuel filter-no change
car has two fuel pumps a pre pump and a high pressure pump
pulled screen from tank-full of rust, so I cleaned that but fuel filter I could not blow through, so injector screens might have rust <---have to test
new spark plugs-no change old ones were all normal color no rich or lean indications or burning oil
plug wires swapped-no change
new cap-no change
swapped rotor-no change
swapped coil-no change
new fpr-no change
new o2-no change
added another ground wire to engine-no change
checked injector pulses and they are firing at those rpms
also I had the exhaust off at the manifold down pipes and it still misfired, popping noise was present from the exhaust, which Im thinking a valve burnt
also did vacuum test and its saying that its not a clog exhaust theres more to the vacuum gauge things too which indicate rings leaking but im not sure if having the exhaust off after the cat is messing with my readings
new timing belt and water pump but is irrelevant, it had the problem prior to these parts
I did compression test and fuel test Ill post that soon but Ill see what you guys think at this point maybe im missing something. also I got a ecu temp sensor but didnt get around to put it in cause its cold out and it requires me to undo stuff I put together already. Only things i didnt get around to do is the injectors,intake gasket but did have the vacuum gauge hook up and indicated that there is no leak but if it is it might be small. thoughts and opinions are appreciated cause I giving up on it, I dont want to keep throwing money at something thats not doing anything. ask away, also I got two repair manuals on this car and no luck with them.
(This post was edited by zinnoberot on Jan 15, 2010, 8:09 AM)
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zinnoberot
Novice
Jan 15, 2010, 8:06 AM
Post #2 of 13
(3443 views)
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compression numbers
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alright heres the compression numbers spec is (142-156)psi
cylinder dry wet
#1 165 psi 174 psi
#2 155 psi 180 psi
#3 145 psi 160 psi
#4 140 psi 159 psi
#5 164 psi 179 psi
#6 180 psi 190 psi
Im gonna say that number 6 seems like it has some carbon build up
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jan 15, 2010, 12:23 PM
Post #3 of 13
(3438 views)
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Re: compression numbers
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That is kinda high for an old car! It might be carbon which has been rare to me for ions but common when leaded gas and poke around use of vehicles happened. I would think plugs would show evidence??
In dinosaur days it was routine to pour water slowly down a warmed up engine would clear it - don't do that! Also ATF and don't do that either. Any of those tricks can cause serious harm.
We used to take a car and just give it a hard run to clear them out too.
I think I'd consider the product called "Deep Creep" which is like shaving cream - far less apt to cause hydraulic lock which would be a disaster! Suggest changing oil in the case it gets in crankcase. Leave something like that overnight or made to spay into running engine's intake. Could foul plugs up.
You could take out all plugs - marked - leave them out and use same. Crank engine with plugs OUT and excess would/should spit out plug holes - use towels so you don't hurt painted stuff.
Probably safest is to use fuel solvents and give it a good run.
See what others suggest before you go nuts with anything,
T
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zinnoberot
Novice
Jan 15, 2010, 12:34 PM
Post #4 of 13
(3432 views)
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Re: compression numbers
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I did the seafoam in the intake a while ago. And now recently I put 10oz in approx five gallons of fuel and still nothing also put 4oz in the crankcase that seem to free up the motor but didnt effect the misfire or bog. I was thinking of running more but if 10oz didnt do much, im not sure if I need more. I havent heard of deep creep yet, Ill look it up. thanks tom for your advice.
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brager
User
Jan 15, 2010, 12:41 PM
Post #5 of 13
(3431 views)
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Re: compression numbers
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when it bogs down does it make any difference or do you notice any
difference whether you have a half tank or full tank fuel?
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zinnoberot
Novice
Jan 15, 2010, 12:47 PM
Post #6 of 13
(3428 views)
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Re: compression numbers
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I havent lately put a full tank in but when I put 3/4 in the one time I did notice it relieved my hesitation from a standstill to wot throttle. also this bog is only in the upper rpm range after I pass 3200, i forgot to mention that, also all the effects of the misfire and bog are in every gear also its an automatic but I dont think its the tranny what so ever. I got to find my fuel pressure specs when I find them Ill post them aswell.
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zinnoberot
Novice
Jan 15, 2010, 6:11 PM
Post #7 of 13
(3419 views)
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alright heres the fuel specs
fuel rate volume is 30oz in 30seconds
I got 28-29oz
fuel pump 92psi (spec is 92-100psi)
fuel pump hold pressure 30psi jumps to 27psi after 5minutes (spec is 80psi) check valve problem im not sure if it has one otherwise its bleeding back through the pump but that shouldnt cause my problems would it?
fuel system energized, engine off 36psi (spec is 36-37psi)
fuel system hold pressure 30psi jumps to 34psi after 5minutes(spec is 30psi) this ones odd
pressure regulator check at idle, vacuum hose attached 28psi (spec is 36-37psi)
pressure regulator check at idle, vacuum hose detached 37psi (spec is 39-40psi)
I need to check the transfer pump pressure and double check the pressures again but I did replace the fpr so I cant remember if I checked it after it. I think I might check to see if my coil is fading out at the misfire also my tach reads the misfire but doesnt drop to zero when its doing it. and all the injectors are firing but I read these low imp. injectors fail at a mid rpm range something about the transition from pulsing to almost being full open, also them clicking doesnt verify them working either. I sat up for hours after hours after hours pretty much four years trying to figure this car out.
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steve01832
Veteran
Jan 16, 2010, 6:25 PM
Post #8 of 13
(3404 views)
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From the description you gave, it sounds like the throttle has to be in the same place every time the problem happens. You may want to take a closer look at the throttle position sensor. If it has a dead spot, it will cut fuel when the wiper goes over the dead part of the coil in the sensor. You can check this with an ohmmeter between the input and signal terminals. Work the sensor by hand slowly as you watch the resistance change. It should be a smooth change with no sharp drop outs.
The ohmmeter will work for this, but, a trace scope is the best method if you can get your hands on one. You will be testing voltage over time if you use this method, much more accurate.
Steve
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zinnoberot
Novice
Jan 16, 2010, 7:32 PM
Post #9 of 13
(3401 views)
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Yeah I change the entire throttle body that has the tps attached, also I verified it is getting power 5volts. Also these tps arent potentiometer styled, they have a two switch style kind. At idle it switches to idle mode and the idle control module starts to work which it starts working my idle control valve and then at wot it ignores the o2 sensor. and I checked the tps like it says in my one manual and at idle posistion your suppose to get continuity and at wot its suppose to get continuity at 8-12 degrees before wot and it does. Yeah its a mind boggler I cant seem to figure it out.
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asleepatdawheel
User
Jan 18, 2010, 2:57 AM
Post #10 of 13
(3383 views)
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I have question about your fuel pressures.. You stated fuel pump 92 psi.. Is that what its rated at or is that fuel pressure reading?? Only asking since you have below,, KOEO pressure at 36 psi,, KOER at 28 psi and below specs by ten psi.. Where did you get the 92 psi reading from?? Also I would check injectors for blockage if you had rust or other contaminants in your fuel system..And make sure the connectors are are properly connected..I would also check voltage at pump to make sure you have proper voltage throughout driving speed..
Also does this engine have a timing belt or timing chain.. Either could be strecthed and cause a slight misfire..
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Its not called bragging,, if you can back it up....
(This post was edited by asleepatdawheel on Jan 18, 2010, 3:14 AM)
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zinnoberot
Novice
Jan 18, 2010, 8:59 AM
Post #11 of 13
(3372 views)
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The 92 psi from the fuel pump, its hooked straight up to the fuel gauge its not teed to any other location. All injectors are firing, but the rust could be causing a problem it was a fine rust so it could have made its way up there, it kinda looked like coffee grinds, but smaller particles that i pulled out of the tank screen. I havent check the fuel pumps voltage at those speeds. I have a new timing belt, but this problem was there prior to me changing it. Yeah im on the verge of pulling the intake manifold with the fuel rail to check injectors but its kinda cold. The car drives perfectly fine up to 2800rpms then it throws a hissy fit, tach bouncing and jerking me forward and back, then i feather it, then it hauls ass but i cant punch it to the floor, but it eventually makes it to 5k. I thought id give another way how to explain it.
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asleepatdawheel
User
Jan 20, 2010, 11:21 PM
Post #12 of 13
(3358 views)
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With All that you have checked and or replaced,, i would say to check the injectors for any blockage and also ohm them to be sure they ohm correctly....It could be that since there is alot of contamination in your fuel system...Cant recall right now but did you check fuel pressure regulator... If not Check that.. Also is the fuel pump in or out of tank...If its in tank,, have you ever dropped tank and looked at it to make sure you have proper line and electrial connections...
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Its not called bragging,, if you can back it up....
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zinnoberot
Novice
Jan 21, 2010, 8:43 PM
Post #13 of 13
(3350 views)
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Yup already checked the injectors ohms, all in spec. Yeah my car has two fuel pumps a 5psi transfer pump and then it goes to the high pressure pump. also you were saying about dropping the tank i looked in there its all good, but the coffee grind rust i got out of the sock, i cleaned that out a long while ago. Also the tank has been dented which prolly made the rust get into the sock. and dropping the tank, I prolly wont be doing that anytime soon lol. The tank wraps around the driveshaft. I put 16oz of seafoam in 5gallons then when it got down to 3 gallons i dumped entire 32oz of marvel mystery oil in, it smoothed some things but not what i was looking for, plus if its rust in my injector screens, all the injector cleaner in the world wont remove it, but i thought id give it a try for other stuff in the injectors. Im gonna see if my ecu temp sensor is part of the problem, I was reading that those sensors change the pulse length of the injectors and timing, also the injectors I have to look at but not until it gets warm here. Id change it, but i have to remove all the stuff i had off already, so that sensors gonna have to wait. oh and fuel pressure regulator its brand new. thanks so far.
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