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View Full Version : Rough engine ideal, where to begin?


fz-e30
08-24-2011, 07:57 PM
sounds more like spark plug went out, but checked the spark plugs by unplugging the cables one by one and noticed a difference in engine performance by unplugging each one. that means the spark plugs are ok!

what would be a usual issue on E30 M42 engine?

egye30
08-24-2011, 11:31 PM
most e30's will idle like crap, what kind of rough idle are you experiencing? like a misfire rough? or are the revs goin up and down on thier own?

fz-e30
08-25-2011, 12:52 AM
i used to have a up and down rev, but then i found a leak on the hose from valve cover to pressure regulator and it was fixed.

Now the rev doesn't go up and down, its sitting below 1000, starting has become a little difficult, have to rev it up a bit to keep it on, then let go of gas slowly so it wont turn off.
it sounds like its ok, then it slows and vibrates too much and so on ...
driving feels less powerful too. feels like its suffocating.

I have changed two of vaccum hoses, but they are from canadian tire and they were slightly tighter. could smaller inside diameter have significant change??

DIY
08-25-2011, 09:59 AM
Prob not its working on the pressure and shouldn't affect performance. If the vaccume is good check compression.

My car idles a but rough when its cold but once it heats up it runs like a pro.
After I fixed my gas tank (2months sitting) I had a prob with the idle where I had to keep the gas on to stop it from stalling out (and slowly leetting off). I kinda think I have a bad ICV but its too expensive for my budget. So I adjusted the throttle body cable until it idle'd better ( and it worked). I still get a very slight vibration sitting while the cars running but I've never known my car not to do that.
Think of it like a diagnostic feature, its your car telling you yes I'm running lol

fz-e30
08-25-2011, 10:21 AM
my oil service light went on too, could scanning it help me find the problem?

who can scan 1991 E30 M42 engine in Toronto?

DIY
08-25-2011, 10:36 AM
Service? Or low pressure light? Change the oil recently? That could def be your prob.
Also you should be able to find out the code without scanning since its obd1 ... There's usually a trick with turning the key on and off ... My E30 uses the 'stomp test'

fz-e30
08-25-2011, 01:59 PM
its the "Oilservice" light thats on plus the Yellow light.
just changed the oil and it went on couple of days after oil change!!!

how do I get the code???
whats a Stomp test??

DIY
08-25-2011, 02:13 PM
I had somebody tell me that the mahl filter (the stock one) actually helps regulate the oil pressure, I've always used fram or k&N without prob but maybe try that,

just google stomp test or E30 codes(I think you have to have a 55pin ecu but its worth a shot) I don't know much about the M42

craigIS
08-25-2011, 03:38 PM
I'm gonna take a shot in the dark, and it's probably not your issue, but if you fuel filter needs changed you can get less power, and shuttering or knocking, but it's prob no that.

To do a stomp test, turn the ignition to the on position (not the start position), but don't start the car, your lights on the dash should be on, and all that jazz. Next, push the accelerator to the floor 5 times, and watch your check engine light. It will come one solid, then after that it will flash. Count the number of flashes. It will go like this:

1 1 1 = 3
1 1 = 2
1 1 1 1 = 4
1 1 1 = 3

3 2 4 3 will be the code.

There will be a pause between numbers, and that's how you know the next number will begin. You will need a pen and paper. right down like I showed above, or just the number you count, and then put it all together, and that will give you the code. Then just look the code up on the net.

daveed
08-25-2011, 03:50 PM
Like m20 cars intake/vacuum leaks will make these cars idle roughly. For the m42 there is a common mod ("mess under the intake mod") to delete a bunch of unnecessary hoses under the intake manifold. Get new vacuum hoses and intake manifold gaskets. Your air/fuel ratio is probably out of wack.

fz-e30
08-28-2011, 03:22 AM
I'm gonna take a shot in the dark, and it's probably not your issue, but if you fuel filter needs changed you can get less power, and shuttering or knocking, but it's prob no that.

To do a stomp test, turn the ignition to the on position (not the start position), but don't start the car, your lights on the dash should be on, and all that jazz. Next, push the accelerator to the floor 5 times, and watch your check engine light. It will come one solid, then after that it will flash. Count the number of flashes. It will go like this:

1 1 1 = 3
1 1 = 2
1 1 1 1 = 4
1 1 1 = 3

3 2 4 3 will be the code.

There will be a pause between numbers, and that's how you know the next number will begin. You will need a pen and paper. right down like I showed above, or just the number you count, and then put it all together, and that will give you the code. Then just look the code up on the net.

I tired it today, but nothing happened. no flashing of check engine light :confused:

DIY
08-29-2011, 02:34 PM
You need a 55pin ecu for that, find your ecu above the glove box and count pins :)

racer-x
08-29-2011, 10:29 PM
Usually vacuum leaks will cause a stall, but it's a great place to start looking.
Timing is next.
Simple tune up, cap, rotor, wires.
Compare the colour of all 6 plugs. They tell you volumes about what's happening internally.
Valve adjustment?
Last but not least, compression and leakdown.

Sorry but my car runs so smooth, I can't tell it's running except for the steady hum of the exhaust!

craz azn
08-29-2011, 10:58 PM
Usually vacuum leaks will cause a stall, but it's a great place to start looking.
Timing is next.
Simple tune up, cap, rotor, wires.
Compare the colour of all 6 plugs. They tell you volumes about what's happening internally.
Valve adjustment?
Last but not least, compression and leakdown.

Sorry but my car runs so smooth, I can't tell it's running except for the steady hum of the exhaust!

That would be all great and dandy if he had an older car...

Timing is dictated by the computer.
M42 doesn't have a cap or rotor.
Only has 4 plugs to check.
And hydraulic lifters don't need adjustment.