What are the symptompts of a bad AFM?
Quote, originally posted by Black_cabbie » What are the symptompts of a bad AFM?
Rough idle, lean or rich running, lousy fuel economy, black smoke, flat spots or hesitation on acceleration can all be caused by AFM problems, but not all at once.
All those symptoms can easily be caused by other problems too.
The flap in the air box can bend, sometimes even break. The printed resistor film can wear thin or through, the resistor can get dirty. The spring can weaken.
What are your symptoms?
Ian, CIS doesn't use an electro/mechanical AFM, you have a fully mechanical sensor plate instead.
Flat spots,hesitation, occasional cutting at low revs (up to 4k then its fine), lousy fuel economy are my symptoms.
In the beginning I thought it was the main fuel pump which I changed (it needed change as it was whinning a lot) but it does it again.
The flap inside is fine and moves freely though.
I changed the ecu and the blue sensor last week but still no luck. I just want to rule out a few things before I start spending here and there with no success.
PS, Sometimes OBD diagnostic DO come in handy
Quote, originally posted by Black_cabbie » .......Flat spots,hesitation, occasional cutting at low revs (up to 4k then its fine), lousy fuel economy are my symptoms........
1st thing, abnormal engine noises, loose or squeaky belts, exhaust rattles, loud lifters. Knock sensor is always listening but cannot tell the difference between spark knock and other noises. The knock sensor controller WILL retard timing and cause all your symptoms if/when it hears noise.
I recall you changed your coolant pump in the last year, did you make certain of an 87° C thermostat? Any other mods to make the cooling system run cooler than stock? I promise, an 87° C thermostat is HUGELY important on DigiFant systems.
All normal tune up stuff still applies, distributor caps deteriorate in as little as 15K miles, faster in wet or damp climates.
You can check operating voltages of the MAF directly at the MAF. Don't bother with resistance values, the ECU doesn't see resistance as such, it reads voltage, the result of resistance.
I don't recall if your car is Digi-I or Digi-II, no matter, the pin outs on the MAF are the same for both except the wire color on pin 3. Pin 3 on Digi-II has a black/blue wire, Digi-I has blue/black. Pin numbers at the ECU are completely different.
Key on, engine off tests as follows;
Pin 3 is reference voltage from the ECU (V-ref), I think you should expect very close to 5.0 VDC.
Pin 4 is ground, due to it's convoluted path to ground, you may see a few milli-volts on it, no more.
Pin 1 is the intake air temp sensor (IAT), voltage will vary according to temperature, use a hair dryer, not a heat gun.
Pin 2 is the MAF potentiometer. Expect 0.1 VDC to 0.5 VDC with the flap at rest, 4.0 VDC to 4.9 VDC with the flap full open. Spend some time on this pin, watch the voltage rise and fall as the flap is opened and closed. The transition should be absolutely smooth with no spikes, glitches or drop outs.
I just took real time, live values from my '92 Digi-I.
Pin 4, 28 mVDC.
Pin 3, 4.93 VDC
Pin 1, 0.8 VDC, outside temp of MAF housing approximately 30° C.
Pin 2, 0.27 VDC at rest, 1.1 VDC at idle, approximately 850 RPM.
Quote, originally posted by Black_cabbie » ......spikes as I move the flap inside.....
This doesn't always work, but it works often enough to be worth a try. Use a pencil eraser on the printed resistor track inside the AFM.
The hard part is getting the cover off without breaking it, it's glued on all around the edges. Use a sharp knife, single edge razor blade and a sharp pick, be patient and persistent. Use about 1/4 as much RTV silicone to glue it back on.