Popping un acceleration

[2700gavin]

All ,
Have come across a problem over the last couple of weeks. When putting my foot down and accelerating quite hard it feels as though there is a momentary loss in power and I get a popping noise / back fire. This might happen two to three times each time I do it. It also feels as there is a slight loss In power at the top end and doesn't feel as quick as it normally is.
After going through the search this is what my possibilities could be and I just need somebody to verify :

1. Issue with pipe work and would need to check all for splits etc
2. Spark plugs may need changing

Can anybody else think of anything else ?

Thanks for any support or advice in advance

[Davezj]

do a boost leak test, this should show up any boost/vac hose issue. it is a very good test to do.

[Trotty]

I would suggest plugs and leads. Most common cause of misfire in boosted engines. Then work through coil breakdown. It will cough and hesitate with vac/boost leak and give bad/worse economy.

[2700gavin]

do a boost leak test, this should show up any boost/vac hose issue. it is a very good test to do.

Dave do you know anybody who has the kit for this ?

[Davezj]

most garages will have the ability to do this test, but i also have the gear to do this test.
as long as it is not and intermittant problem then it should be fairly easy to diagnose, but if it only happens sometimes then it can be a real problem to get to the bottom of and you end up swapping stuff for the hell of it and don't know if it has fixed anything without laeving it in the car for a week and testing it every day to see if fixes the issue.

you can do a little water spray test as well, just spary the coil packs and leads with a little water and see if anything breaks down. It will cause any harm but it may cause the engine to run rough if there is obvious break down, untill everything drys off.
then there are the plugs. i tend to do the esiest things first, because i can. saves removing anything from the engine before diagnosing the issue or at least knowing what it is not.

[nos monkeys]

i pretty much have the same problem, its fine driving it for awhile but sometimes after a long drive or an hour drive it will start missing under boost. i just had my plugs changed last week when the cambelt was done and the mitsi place said they did a boost leak test and said its fine and the engine has no problems. . . . i thought it was the pod sucking up hot air but done it again today when driving back home.

it mainly does it in first but if i put my foot down in first then it starts missing and when i change to 2nd and put my foot down it continues to miss, but if im driving on the open road and put it in 3rd or 4th it boosts fine with no missing. theres no error codes either.

can someone point me the right direction or tell me what ohm the leads should be so i can check out my leads. i dont think its a boost leak or plugs because they said they have changed them and checked, although ill do that last if it still happens after i check the leads.

but it doesnt do this all the time, yesterday i drove it 4 hours straight and it was fine i thought it was fixed after putting the stock intake on, driving home today it seemed fine since i was sitting on the open road and using 3rd/4th sometimes over taking but as soon as i get to town at the lights put my foot down in first and boom starts missing/hesitation

[Davezj]

misfire is generally a electrical issue but not always.

nos monkey, what plugs were fitted and what gap did they use?
if you don't know then check one of the front ones and measure the gap on that. is the garge you used a trusted place, did the garage complain that the plugs were a pain in the arse to change if not then the rears might not have been changed. as a short cut and they just kept the 3 plugs they did not fit. a bit synical i now but it has been done before.

try the spray test with water on the coil pack and leads to see if they break down and arc when wet, if they do then chage the offening parts and that should make things better.

it sounds like when you are on the move things are being kept resonabley cool via air flow through the engine bay and when in town the heat builds up and thing start failing intermitantly.
Do you have any other members locally, you could do a swap of coilspack and leads a nd see if it fixes it if not then you don't need to waist mony replacing them.

it maybe inlet air temp related. do you have a pod filter in the engine bay, if so at low speed round town it will be sucking in really hot air and causing an issue.

have a look at the jap workshop manual pdf here,
http://www.clubvr4.com/forum/showthr...hop+manual+pdf
compare the index page of the english index page linked further down the page
http://www.clubvr4.com/forum/showthr...orkshop+manual
and scroll through the engine electrial section and you should come to the point where you see a picture of the coil pack and lead and the actual resistance values will be there.
see what the coil resistance should be, i believe it is around 15.3K -20.7K Ohms when you measure across the outputs of the coil packs. you are measuring the resistance of the seconary coil within the coil pack. you might think it should be a lower resistance than 15.3K -20.7K Ohms as it is only a coiled up bit of wire but this bit of wire is massively long and wire does have resistance per unit length.
The believe the lead will be about 14K Ohms.

[nos monkeys]

it did have a pod but i replaced it with the stock intake with a k&n panel filter, all was good thought it was fixed drove 4 hours without a noticeable problem till the way home it started doing it again, there is 1 guy here local with a super vr4, not sure if they have the same coils/leads and not sure if he would help out although i did send him a private message. if it is intake air temp would i broken air intake sensor throw a code? although i dont think its air intake as im 99% sure it sounds like spark related but i could be wrong.

if it was a coil pack breaking down would that throw a code? i took it to Mitsubishi dealers to get the cambelt done and told them to look over the car and check everything. although they failed to tell me my ayc diff is stuffed and grinding which i knew that but was hoping they would tell me as well but didnt, so im not sure how good they were

Will go and measure the resistances and check the leads with some water once the rain calms down a bit.

[Davezj]

coil pack are the same across all models of vr4. there may have been a slight change in design at one point but they are all interchangable. same with the leads.

i harsh misfire will get recorded as a error code but most mild misfire do not record a code.
but read them anyway, it cost nothing to do and is a good thing to do on a regular basis. as a lot of codes that are recorded you would not know they have occured, but it may effect efficiencey and power but not enough to be noticed.

personally i don't trust any garage enough to get them to work on may car, and due to this i save myself a fortune in servicing cost.

[nos monkeys]

yeah i drove i around for about 5minutes when it was missing to see if it would show up a code but it still never did, hoping to check the leads and coils and front 3 plugs tomorrow and try eliminate some of the list

[nos monkeys]

misfire is generally a electrical issue but not always.

nos monkey, what plugs were fitted and what gap did they use?
if you don't know then check one of the front ones and measure the gap on that. is the garge you used a trusted place, did the garage complain that the plugs were a pain in the arse to change if not then the rears might not have been changed. as a short cut and they just kept the 3 plugs they did not fit. a bit synical i now but it has been done before.

try the spray test with water on the coil pack and leads to see if they break down and arc when wet, if they do then chage the offening parts and that should make things better.

it sounds like when you are on the move things are being kept resonabley cool via air flow through the engine bay and when in town the heat builds up and thing start failing intermitantly.
Do you have any other members locally, you could do a swap of coilspack and leads a nd see if it fixes it if not then you don't need to waist mony replacing them.

it maybe inlet air temp related. do you have a pod filter in the engine bay, if so at low speed round town it will be sucking in really hot air and causing an issue.

have a look at the jap workshop manual pdf here,
http://www.clubvr4.com/forum/showthr...hop+manual+pdf
compare the index page of the english index page linked further down the page
http://www.clubvr4.com/forum/showthr...orkshop+manual
and scroll through the engine electrial section and you should come to the point where you see a picture of the coil pack and lead and the actual resistance values will be there.
see what the coil resistance should be, i believe it is around 15.3K -20.7K Ohms when you measure across the outputs of the coil packs. you are measuring the resistance of the seconary coil within the coil pack. you might think it should be a lower resistance than 15.3K -20.7K Ohms as it is only a coiled up bit of wire but this bit of wire is massively long and wire does have resistance per unit length.
The believe the lead will be about 14K Ohms.

Had a read of that manual and got the right numbers down but um could someone tell me how to check the coil packs lol i cant quite get my head around where to put the 2 ends of the multi meter? do i use it on the pins on the coil where the plug plugs into?

ok never mind i got it lol i think, i put the multimeter on the spark plug ends of the coil correct? i had a spare coil in the boot i think was an old one but i checked that and it was reading 17.5k ohm. the first coil in the car i done has read 19.3k ohm im just taking the other 2 out now to check them

[Davezj]

yes you are you doing the correct measurement.
but just because the resistance measurement is ok does not mean it will not break down under load, that is why i suggested the water spray, at idle to any breakdown, then wet them again and go for a drive to see if the misfire gets worse, if it does not them you can assured the coil pack and leads are OK.

[nos monkeys]

Cheers, i did spray them with water yesterday and it didnt miss at all, i got 19.3k ohm on 2 of the coils but i cant get any reading off the last one . . . my meter is fine but somehow it wont get any readings, once i get this checked ill go for a drive then spray them with water and go for another drive.

also i dont have a feeler gauge to measure my sparkplug gap but the front 3 plugs look ok, will put a photo of them shortly. they are bosch platinum plus FR7DPX

still cant get any readings off the last coil no idea why but putting it back on and will go for a drive and hopefully it will start missing so i can try find the fault

[Davezj]

that doesn't sound good on the coil pack that does not get a reading off it. have you rechecked the spare coil pack, just to make sure you can still measure that one.
if you still cannot get a resistance reading that might be you issue. a good test for this is with the engine at idle, disconnect the low voltage power connector off this coil pack and see if it make a difference to the engine running,
if it does, then connect it back up, then just remove the plug lead to te rear cylider (you will want to switch the engine off to do this, less chance of a nice shock) see if that makes a difference to the engine running. if not then it could be the coil pack not giving a spark to the rear cylinder. if the engine is running on 5 cylinder, you may not be able to tell just by listening to it.

[nos monkeys]

have just started it and as normal its running fine, i did check the coil in the boot it read 17.5k ohm and i swapped the coil i couldnt get a reading with the coil that is able to be taken out without removing the y intake pipe so i can remove it easier. am about to take it for a drive and it will probably run without a problem then ill come back and try some water then take it for another drive to check.

90% of the time the car runs without a problems its just after a drive is where it starts missing. i dont think the plugs were replaced though they look good but not new. here is a picture, all 3 front plugs look the same as this none are any different.

how would i tell if its a spark plug breaking down?

[Davezj]

have just started it and as normal its running fine, i did check the coil in the boot it read 17.5k ohm and i swapped the coil i couldnt get a reading with the coil that is able to be taken out without removing the y intake pipe so i can remove it easier. am about to take it for a drive and it will probably run without a problem then ill come back and try some water then take it for another drive to check.

90% of the time the car runs without a problems its just after a drive is where it starts missing. i dont think the plugs were replaced though they look good but not new. here is a picture, all 3 front plugs look the same as this none are any different.

how would i tell if its a spark plug breaking down?

i would say they are not new plugs, quite a lot of carbon build up on the bottom thread ring, how long since they were supposed have been changed?

[nos monkeys]

well i got the cambelt done 2 weeks ago and told them i wanted a full 120k service which they said included plugs and fluids as well because i have no idea about the history of this car since all the receipts i was given were photo shopped. I just went for a 30km drive, it went fine but it did miss a couple times on the way back, i pulled up the drive covered the coils in water then took it back out to see if it got worse, first 3 pulls were no problems then the last one it started missing, no idea if it made it worse than normal or not though because it only did it 1 out of 4 times. by the time i got home all the water had evaporated off

grr this unpredictable missing =[


So i realise now that since its sunny and hot outside my ohms rise lol, i checked that 1 coil that i couldnt get a reading before and it was like 21.7k was thinking it was high and thats the faulty one but then i checked the other 2 coils and they both were 21.8k ohm. the one in my boot is still 18.3k ohm but its not hot like the others.


I got a guy here to take it for a drive and as normal it didnt really play up much but it did do it a little bit and he said it sort of feels like fuel cut. but i have no idea i checked the coils and leads and there ok doesnt matter if its wet or dry it doesnt make a difference and its to unpredictable to diagnose yet so ill just leave it for now untill it gets worse or better. but we both have no idea what it is.

thanks for your help anyway at least i learnt how to check my coils and all that

[Davezj]

fuel cut is a complete loss of power even when you keep your foot on the throttle for about 0.5 second, then the power comes back comes back.If you keep you foot down it iwill do it again about a couple of seconds after the first time.
you can check if fuel cut by lowering the boost if you have external control on it MBC EBC.

[nos monkeys]

that is what it feels like most the time i just thought it was missing because i just never thought it could be fuel cut because its only running 7psi. Unless its boost spiking before it settles at 7psi but im not sure if thats possible. Everything is hooked up to the stock boost solenoid which i think is broken since stock boost for a manual is 9psi, its only running 7psi according to the mitsi shop but my boost gauge is broken and only reads 5 so im not 100% sure.

When i brought the car it was free boosting for probably a good 6months + also the vaccum line which is ment to run to that fuel pressure regulator ( i think thats what it is) the vacuum port on the end of the fuel rail was disconnected and just hanging there which was probably also had been disconnected for a very long time and a few other vaccum things which were just hanging lose. I'm not sure if having the fuel regulator disconnected for so long would cause it to not work properly now when its on boost ( assuming that is what helps add more petrol when on boost) everything is all hooked up back to how its meant to be now but unsure if having it off for so long would cause problems now.

[Davezj]

If the vac/boost line is not connected to the factory fuel pressure regulator then the fuel pressure will not rise with the boost pressure. and having no boost to the wastegates means it would boost as hard as it could all the time.

1 the FPR disconnected would probably make the engine run lean when it was boost normally.
2. no boost control on the wastegates would make the engine even leaner due to the high than normal boost which would make it worse.
3. if running with no boost control to the wastegates then as long as the fuel cut level has not been changed in the ECU or the car has not had a fuel cut defender fitted, then as soon as you tap the accelerator pedal you will hit fuel cut every time you go near the accelerator. very very obvious, it would make the car almost undrivable.