Misfire/engine hunting/power loss
10-25-2014, 06:07 PM
#1
Racer
Thread Starter
Misfire/engine hunting/power loss
Dear All,
Had my long oil line replaced (from oil filter to thermostat) by a garage, and while they were driving it out of the workshop, the throttle stuck on at about 5,000rpm.... on its own. They sprayed it with WD40 and the car worked ok.
When I took delivery of the car it was running ok'ish, but after warming up the engine felt 'heavy' and down on power, kept bogging down and at junctions it would tick over like an engine mount had gone, rocking the car, which I guess was a cylinder not firing.
First thoughts were to clean the microswitch on the throttle incase they'd soaked it with WD40, check the ICV incase there was an overfill (which was sticking but not full of oil) and look to see that the distributor belt was spinning. All ok. Next I pulled the coil lead out of the 1st coil and tried to start the car..... wouldn't stat, so I tried the same on the 2nd with the same results. Is this test meant to be done with the car running?
Now I cant really understand why they would have dislodged a spark plug wire doing an oil pipe, but I've checked the uppers which all seem fine, I haven't got access to a lift to get to the lowers.
What else should I check?
Mark 90C2.
Had my long oil line replaced (from oil filter to thermostat) by a garage, and while they were driving it out of the workshop, the throttle stuck on at about 5,000rpm.... on its own. They sprayed it with WD40 and the car worked ok.
When I took delivery of the car it was running ok'ish, but after warming up the engine felt 'heavy' and down on power, kept bogging down and at junctions it would tick over like an engine mount had gone, rocking the car, which I guess was a cylinder not firing.
First thoughts were to clean the microswitch on the throttle incase they'd soaked it with WD40, check the ICV incase there was an overfill (which was sticking but not full of oil) and look to see that the distributor belt was spinning. All ok. Next I pulled the coil lead out of the 1st coil and tried to start the car..... wouldn't stat, so I tried the same on the 2nd with the same results. Is this test meant to be done with the car running?
Now I cant really understand why they would have dislodged a spark plug wire doing an oil pipe, but I've checked the uppers which all seem fine, I haven't got access to a lift to get to the lowers.
What else should I check?
Mark 90C2.
10-25-2014, 06:12 PM
#2
Nordschleife Master
Don't do the coil isolation test by removing the ignition leads. Instead disconnect the ignition module at each coil (while the car is turned off) and see if it runs on each module by itself.
You can see the ignition modules and the plugs you need to disconnect at the bottom of this frame.
Those thin metal bars, depress them while you disconnect the connector.
You can see the ignition modules and the plugs you need to disconnect at the bottom of this frame.
Those thin metal bars, depress them while you disconnect the connector.
10-25-2014, 11:45 PM
#7
Race Car
Someone once installed my distributer caps backward. This put them at an angle. Not good.
Also. It takes 4.5 turns on a plug end to screw the plug end to the wire. On either side. So also on mine, unknown to me, it seems on a few wires over time, who ever was re-plugging in the wires turned a few a half turn counter clockwise and eventually the were no longer screwed in...
Take a multi meter to each wire, and check resistance. If each one is 3ohm, then you at least know you are conducting. This doesn't test for leaks, but it'll tell you if electricity is getting from the cap to the plug.
Also. It takes 4.5 turns on a plug end to screw the plug end to the wire. On either side. So also on mine, unknown to me, it seems on a few wires over time, who ever was re-plugging in the wires turned a few a half turn counter clockwise and eventually the were no longer screwed in...
Take a multi meter to each wire, and check resistance. If each one is 3ohm, then you at least know you are conducting. This doesn't test for leaks, but it'll tell you if electricity is getting from the cap to the plug.
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10-27-2014, 04:53 AM
#9
Racer
Thread Starter
Ok, so yesterday I did 'a hemi-manifoldectomy'and found a fair amount of oil in the inlet tract, which I cleaned out. Although the car is a lot 'sharper' in power delivery the cr4p idle and hunting/surging issues remain. The revs even 'bounce' as it would with an ISV issue, which is clean but was originally sticking. The AFM doesn't appear to be contaminated with oil either,malthough I didn't open it up. I guess I need the scan-tool.........
10-27-2014, 05:31 AM
#10
Three Wheelin'
It only takes the smallest of vaccum leaks to make these engines run like a dog. The hunting/surging issue you describe would send me in this direction.
Whilst the scan tool is good to have in your tool box, I'm doubtful it'd show up anything relevent for your case. A malfunction of any of the engine sensors (excluding the crank position sensor, which we can rule out as it does kind of run) will not prevent the engine from cold starting.
Whilst the scan tool is good to have in your tool box, I'm doubtful it'd show up anything relevent for your case. A malfunction of any of the engine sensors (excluding the crank position sensor, which we can rule out as it does kind of run) will not prevent the engine from cold starting.
10-27-2014, 06:29 AM
#11
Racer
Thread Starter
The car starts and drives, it just runs like its on 4/5 cylinders, jumps, skips and stutters etc. it even pops on downshifts as the revs surge and I slow down using the gears. Its almost like in an 'old fashioned' car when the choke was stuck out...........
I don't think there's a vacuum issue because I hear the pressure release when I disconnect the vacuum pipe from the back of the air box.
I don't think there's a vacuum issue because I hear the pressure release when I disconnect the vacuum pipe from the back of the air box.
10-27-2014, 07:06 AM
#12
Three Wheelin'
>I don't think there's a vacuum issue because I hear the pressure release when I disconnect the vacuum pipe from the back of the air box.
You would do, that line is controlled by a solenoid. ie with the engine off, the valve will be shut so no route through to the plenum.
Still sounds like an air leak to me
How about the vaccum line that runs down to the fuel pressure regulator? Is it connected properly? and more importantly is it dry? If its damp with fuel inside at the reg end then this is indicative of the regulator on the way out (which could also give the symptoms you describe).
You would do, that line is controlled by a solenoid. ie with the engine off, the valve will be shut so no route through to the plenum.
Still sounds like an air leak to me
How about the vaccum line that runs down to the fuel pressure regulator? Is it connected properly? and more importantly is it dry? If its damp with fuel inside at the reg end then this is indicative of the regulator on the way out (which could also give the symptoms you describe).