Lt1 injector pulse width = 0?
Thread Starter
Burning Brakes
Joined: Feb 2002
Posts: 1,232
Likes: 28
From: South Riding VA
Lt1 injector pulse width = 0?
94 lt1
I'm chasing the intermittent surging and poor idle when stopped and in gear problem. When I capture the data stream at idle I see my injector L and R pulsewidth at 0 sometimes. It looks to vary up to 4 when I increase throttle. My scan tool lists the units as mV ( I would have thought it'd be in ms). Any thoughts on the 0? When I read up on the pulsewidth control the fsm said that the o2 sensor is the primary control in closed loop... Could the 0 be pointing me to an o2 issue . ( o2 sensors look to vary as they are supposed to)
I'm chasing the intermittent surging and poor idle when stopped and in gear problem. When I capture the data stream at idle I see my injector L and R pulsewidth at 0 sometimes. It looks to vary up to 4 when I increase throttle. My scan tool lists the units as mV ( I would have thought it'd be in ms). Any thoughts on the 0? When I read up on the pulsewidth control the fsm said that the o2 sensor is the primary control in closed loop... Could the 0 be pointing me to an o2 issue . ( o2 sensors look to vary as they are supposed to)
Safety Car
Joined: Apr 2011
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I would think so...
The O2 sensor is simply a generator. The thing produces a voltage that is used as a guide to adjust fuel. If the sensor is dying or so dirty that its not getting a taste of the gasses..no voltage. IIRC they are supposed to have a min, but I cannot say if thats true for one thats damaged or simply old and tired. I'd go thru the connections as well to be sure its not something that simple.
Good luck
The O2 sensor is simply a generator. The thing produces a voltage that is used as a guide to adjust fuel. If the sensor is dying or so dirty that its not getting a taste of the gasses..no voltage. IIRC they are supposed to have a min, but I cannot say if thats true for one thats damaged or simply old and tired. I'd go thru the connections as well to be sure its not something that simple.
Good luck
Thread Starter
Burning Brakes
Joined: Feb 2002
Posts: 1,232
Likes: 28
From: South Riding VA
So is 0 an impossible reading? On the surface it sounds like it would be ( injectors not firing at all?) because the car is still running. Does the PCM shut down the injectors for any reason? In open loop I seem to see a pulsewidth of 4 for most/all of the frames.
Race Director
Joined: Apr 2002
Posts: 10,036
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From: Anaheim CA
The ECM shuts down the injectors when you're coasting. There is a minimum speed (MPH) for this. I think there's also a minimum RPM, as there is code to keep the engine from stalling.
The injectors will not fire if the ECM doesn't see a signal from the VATS module.
The injectors are synchronized to the rotation of the engine by the DRPs (Distributor Reference Pulses) and they will not fire if the ECM doesn't see those DRPs.
Your scan tool should be seeing the injector pulse width in ms. There is a minimum pulse width specification. On my car it's 1.6 ms. Basically the ECM calculates the pulse width and if it's less than 1.6 ms. then it uses 6 ms. That's why you can't put really big injectors in your car. The ECM can't lower the pulse width enough for it to idle well.
The injectors will not fire if the ECM doesn't see a signal from the VATS module.
The injectors are synchronized to the rotation of the engine by the DRPs (Distributor Reference Pulses) and they will not fire if the ECM doesn't see those DRPs.
Your scan tool should be seeing the injector pulse width in ms. There is a minimum pulse width specification. On my car it's 1.6 ms. Basically the ECM calculates the pulse width and if it's less than 1.6 ms. then it uses 6 ms. That's why you can't put really big injectors in your car. The ECM can't lower the pulse width enough for it to idle well.
Last edited by Cliff Harris; May 10, 2013 at 11:58 PM. Reason: Corrected minimum pulse width value.
Thread Starter
Burning Brakes
Joined: Feb 2002
Posts: 1,232
Likes: 28
From: South Riding VA
Ok I've confirmed with the tool folks that the units displayed is an error in their software, it should be ms. It looks like 0 pw is a valid reading under some circumstances however I see it while the car is in park and idling. I get readings that range from 0 to 4. The last recording showed 4 ms steady during open loop, others had some 0s in there... Maybe a short somewhere?
Race Director
Joined: Apr 2002
Posts: 10,036
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From: Anaheim CA
To go back to your original post concerning how the injector pulse width is calculated, my recollection is that the ECM starts with the appropriate BLM and then adds for coolant temperature and some other stuff which I don't recall right now.
The BLMs are adjusted by the INT, which is the instantaneous calculation of O2 reading and some other stuff. I think the MAF and TPS are involved. Basically the ECM compares the INT to the BLM and if the INT is consistently higher or lower it tweaks the BLM in the same direction.
The BLMs are adjusted by the INT, which is the instantaneous calculation of O2 reading and some other stuff. I think the MAF and TPS are involved. Basically the ECM compares the INT to the BLM and if the INT is consistently higher or lower it tweaks the BLM in the same direction.
Thread Starter
Burning Brakes
Joined: Feb 2002
Posts: 1,232
Likes: 28
From: South Riding VA
This all brings up another interesting question: what should I see when I look at the data stream for pulse width, one number or 4 values for each bank ( 8 total - one for each injector)
Since the 94 LT1 is a sequential system, shouldn't I see a value for each injector? I'm specifically looking at the following PIDs:
Inj L pw
Inj R pw
I currently only see one value for each... And sometimes it's 0 for extended periods of time.
Since the 94 LT1 is a sequential system, shouldn't I see a value for each injector? I'm specifically looking at the following PIDs:
Inj L pw
Inj R pw
I currently only see one value for each... And sometimes it's 0 for extended periods of time.
