bmhor Posted September 21, 2009 Share Posted September 21, 2009 I'm looking at a friends 90 which has a late 3.9 (serp belt) engine fitted and is running rich. There are no cats fitted and has the green tune resistor. I've been through all the electrical tests in the manual and the only thing I've found were 2 bad connections on the connectors for injectors 1 & 3 What I need to do now is measure the injector pulse length HOWEVER my meter only gives frequency..... Is there a way to work out from the freq. what the pulse length is??? The freq measured at idle is 11 - 12 Hz Bob Quote Link to comment Share on other sites More sharing options...
Retroanaconda Posted September 21, 2009 Share Posted September 21, 2009 Time period (in seconds) = 1 / frequency (in hertz) Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted September 21, 2009 Share Posted September 21, 2009 Period is not duty cycle. Easy way is to measure the DC volts on the ECU side of the injector, if it was at 100% duty cycle the ECU side would basically be permanently at 0v, at 0% it would be at 12v. The pulses should be fast enough that the meter will spit out a very approximate average reading. The frequency will always be a multiple of engine RPM as (from memory) it squirts twice per rev, as triggered by the dizzy. What I want to know is what are you going to do with this information? The injectors are banked (4+4) so there's no real way two of them can be triggered for a different amount of time to the rest of them. If it's running rich the #1 suspect is temperature sensing: Try checking the coolant sensor, failing that the air temp sensor is built into the airflow meter, or it could be the AFM itself is a bit dodgy. Quote Link to comment Share on other sites More sharing options...
woodytz Posted September 21, 2009 Share Posted September 21, 2009 Dont forget your fuel pressure, check at idle with vac connected approx 35 psi, with it disconnected aprrox 40 psi. cheers woodytz Quote Link to comment Share on other sites More sharing options...
bmhor Posted September 25, 2009 Author Share Posted September 25, 2009 Time period (in seconds) = 1 / frequency (in hertz) When you work this out it gives a time of about 83 ms Divided by 2 (no of banks) and 4 (no of cyls per bank) gives a cycle time of 10ms and your looking for about 2ms at idle....... I wonder if the meter can measure the % of the cycle used???? Bob Quote Link to comment Share on other sites More sharing options...
bmhor Posted September 25, 2009 Author Share Posted September 25, 2009 What I want to know is what are you going to do with this information? The injectors are banked (4+4) so there's no real way two of them can be triggered for a different amount of time to the rest of them. If it's running rich the #1 suspect is temperature sensing: Try checking the coolant sensor, failing that the air temp sensor is built into the airflow meter, or it could be the AFM itself is a bit dodgy. I appreciate that the injectors are banked and the bad connections have been fixed OK but having checked all the electrical sensors as per L/R workshop manual and everything is within spec at cold and at temp, what else can I do? Compression tests shows all OK Any suggestions????? Bob Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted September 25, 2009 Share Posted September 25, 2009 When you work this out it gives a time of about 83 ms Divided by 2 (no of banks) and 4 (no of cyls per bank) gives a cycle time of 10ms and your looking for about 2ms at idle....... Erm, what? All the frequency is telling you is how many times per second the injectors are firing - not for how long. As I said, the frequency will be something like 1/2 engine RPM. Frequency is not duty cycle. If you think the injectors are open for too long (eg too much fuel going in) then it'll be because the ECU thinks there should be more fuel going in. Look for the cause not the symptom - you don't put out a fire by taking the battery out of the smoke alarm. I suggest the EFI fault finding manual in the tech archive, work through it and report back anything that's not right. Quote Link to comment Share on other sites More sharing options...
Highway_Star Posted September 25, 2009 Share Posted September 25, 2009 If it's electrically all good, and there's no daft air leaks or sensor problems.... Bob, I'm assuming you mean running rich at idle? Or at revs? If it's at idle then a simple twiddle of the mixture screw on the AFM should sort it. Assuming that base idle speed and throttle linkages and disc are set up correctly. If it's at revs.... In my experience the Hotwire system runs lean across the range if anything. Some half assed attempt at fuel economy Has the ECU been chipped? I tried a Tornado chipped ECU in mine, the chip was a for a 4.2. It was not a succesful experiment. If you're hell bent on measuring the injector pulse length, I've an oscilloscope you're welcome to a play with. It can be rented in the standard currency of 1/2 NATO and hub nuts Quote Link to comment Share on other sites More sharing options...
SteveRK Posted September 25, 2009 Share Posted September 25, 2009 has the engine ever run properly? The ECU when Lambda sensors are fitted will always try and adjust the mixture by varying the injector pulse length to bring it back to within spec' - but only up to a point. If a sensor or air flow meter is slightly out of spec' (up to a point) the ECU should try and adjust the injector pulse length accordingly to bring the Lambda sensor feedback in line with spec' If the Lambda sensors have been removed then the ECU will likely default to a pre-set fuel map as it has no feedback as to how rich/weak the exhaust emissions are? Quote Link to comment Share on other sites More sharing options...
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