Problem with how my Chim's engine is running.
Discussion
Hello all.
My Chim has done 55,000 miles. "R" reg, 1998 4.0 litre.
This evening was out in it and after about 20 miles or so the car started "holding back" intermittently. Carried on (as I felt whilst it was running I'd try and get it home) and it became worse and as I was driving along it was as if the car was "hic-cupping". It almost felt as though the car was suffering from intermittent fuel starvation as opposed to an electrical mis-fire. Once home (a total of about 38 miles) I let the engine idle and at idle the revs dropped as low as 500 rpm then raising to about 1500 rpm then back to 500 rpm etc., etc.
If anyone would be kind enough to offer some thoughts on what might be the problem - and how I can fix it of course - I would be very grateful.
Could the "holding back/hic-cupping" be linked to the poor idling?
Thank you.
Scrubbie.
My Chim has done 55,000 miles. "R" reg, 1998 4.0 litre.
This evening was out in it and after about 20 miles or so the car started "holding back" intermittently. Carried on (as I felt whilst it was running I'd try and get it home) and it became worse and as I was driving along it was as if the car was "hic-cupping". It almost felt as though the car was suffering from intermittent fuel starvation as opposed to an electrical mis-fire. Once home (a total of about 38 miles) I let the engine idle and at idle the revs dropped as low as 500 rpm then raising to about 1500 rpm then back to 500 rpm etc., etc.
If anyone would be kind enough to offer some thoughts on what might be the problem - and how I can fix it of course - I would be very grateful.
Could the "holding back/hic-cupping" be linked to the poor idling?
Thank you.
Scrubbie.
Unfortunately it could be one of many things, plugs, leads, cap, rotor, coil, ignition amp, MAF, Stepper Motor, injectors, fuel/ecu relay connections, fuel regulator etc.
Start with the easy and simple jobs and work back, check the dizzy cap/rotor for signs or arcing, give both a good clean up and see if things improve.
It would help if you have someone nearby who either has spares or would be willing to swap known good parts to test the issue.
Do you have or know anybody who has Rovergauge/ECUmate who could read any fault codes you may have?
Here are some basic steps for how to check/test the MAF & clean the Stepper Motor
Testing AFM
1. Insert the negative probe into the Red/Black wire (sensor ground), and the positive into the Blue/Green wire (Airflow signal).
2. Turn on the ignition, but do not start the engine.
3. The meter should immediately indicate a reading of approximately 0.3-0.34 Volts. Most defective airflow meters will overshoot to 0.8 Volts or higher, and take at least 2 seconds to come down to the correct voltage.
4. Now start the engine, and the reading should rise to 1.6 Volts (3.5 Litre engine) to 1.75 Volts (5.0 Litre engine).
Cleaning The Stepper Motor
1) Get the car warm
2) Remove the stepper from the plenum and reconnect it. Block the hole where the stepper was with some sort of bung or strong tape to prevent air ingress.
3) Hold the stepper in your hand, so you can catch the central cone and spring when it comes out.
4) Get someone to start the car. Without the stepper in place it will rev at around 2k- 2.5k (This is noisey!!), but the ECU will try to slow it down by powering the stepper motor and pushing cone outwards. It will do this in a series of pulses, a few seconds apart, until the cone and spring drop out. (assuming they are not completely stuck). It may take a bit of manual help to get the cone to fully release. Now stop the engine and let it cool.
6) Clean all the muck of the shaft, and lightly lubricate the screw thread inside the motor.
7) To reassemble, wind the shaft back into the motor so far, but align the slot in the shaft with the plastic keyway as best you can by rotating the shaft in its screw thread
8)With the engine cool, then reconnect the stepper motor. Power cycle the ignition on and off, (don't start) and the ECU will try to pull the shaft back in each time the ignition is turned OFF. This is the slightly tricky bit, as if the keyway and shaft are not quite aligned it wont pull home, so you may need a few attempts.
Start with the easy and simple jobs and work back, check the dizzy cap/rotor for signs or arcing, give both a good clean up and see if things improve.
It would help if you have someone nearby who either has spares or would be willing to swap known good parts to test the issue.
Do you have or know anybody who has Rovergauge/ECUmate who could read any fault codes you may have?
Here are some basic steps for how to check/test the MAF & clean the Stepper Motor
Testing AFM
1. Insert the negative probe into the Red/Black wire (sensor ground), and the positive into the Blue/Green wire (Airflow signal).
2. Turn on the ignition, but do not start the engine.
3. The meter should immediately indicate a reading of approximately 0.3-0.34 Volts. Most defective airflow meters will overshoot to 0.8 Volts or higher, and take at least 2 seconds to come down to the correct voltage.
4. Now start the engine, and the reading should rise to 1.6 Volts (3.5 Litre engine) to 1.75 Volts (5.0 Litre engine).
Cleaning The Stepper Motor
1) Get the car warm
2) Remove the stepper from the plenum and reconnect it. Block the hole where the stepper was with some sort of bung or strong tape to prevent air ingress.
3) Hold the stepper in your hand, so you can catch the central cone and spring when it comes out.
4) Get someone to start the car. Without the stepper in place it will rev at around 2k- 2.5k (This is noisey!!), but the ECU will try to slow it down by powering the stepper motor and pushing cone outwards. It will do this in a series of pulses, a few seconds apart, until the cone and spring drop out. (assuming they are not completely stuck). It may take a bit of manual help to get the cone to fully release. Now stop the engine and let it cool.
6) Clean all the muck of the shaft, and lightly lubricate the screw thread inside the motor.
7) To reassemble, wind the shaft back into the motor so far, but align the slot in the shaft with the plastic keyway as best you can by rotating the shaft in its screw thread
8)With the engine cool, then reconnect the stepper motor. Power cycle the ignition on and off, (don't start) and the ECU will try to pull the shaft back in each time the ignition is turned OFF. This is the slightly tricky bit, as if the keyway and shaft are not quite aligned it wont pull home, so you may need a few attempts.
Speculation is a dangerous game- you can introduce faults as you go about swapping things, at this stage you dont even know if its ignition or fuel. First pull out a plug and check its colour. If the AFM output has gone high it will flood the engine and heavily soot the plugs. The ECU (fuel side of things) also has inbuilt diagnosis that may throw up a fault code if you have access to ECUmate or Rovergauge (ask nicely if someone has one near by). It wont be the stepper if the idle is dropping in this case- simply that the engine is dropping one or more cylinders so the stepper simply cant control the idle with that big drop in power. Certainly a faulty amp, coil, king lead or rotor arm can cause these issues- its worth looking at the engine in the dark when its running to see if you have any arcing around the HT components, but its not easy to check coil or amp performance without the right test gear to measure the HT voltage. An old style garage with a crypton tune may be able to do a check on the HT waveforms to see if they are correct if there is nothing obvious to see.
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