MAF readings

[Injuhneer]

What MAF readings do you folks get from your truck while it is running?

I am seeing curiously low readings from my truck (OBDII - ELM327 adapter / Torque Pro) of around 5-20 (upper mid RPM range WOT). I am still determining if the ECU in my truck has gone stupid or is the MAF yet another failure.

 

[mbrummal]

Could it be the value is going high enough to change the unit (g/min to kg/min) but your reader doesn't reflect the unit change?

Have you tried using a standard plug-in (not wireless) OBD code reader?

 

[rovercanus]

What are your symptoms?

 

[discostew]

What are your symptoms?

Why you always gotta be so logical? Why would you start with symptoms before fixing shit?

 

[jafir]

It's normal for GEMS (maybe just the advanced evap version, I'm not sure) to show MAF readings that are off by a factor of like 10 or 100 or something. People always complain that ultragauge shows something stupid like 1000 mpg because of it.

 

[rovercanus]

Why you always gotta be so logical? Why would you start with symptoms before fixing shit?

That's how I roll.

 

[discostew]

well then riddle me this rovercanus.. How come nobody on this board ever thinks a wire or connection with excessive resistance is a possible cause? It's always gotta be the module if it wasn't the sensor. Am I being to logical? I almost never see a module fail anymore, but I make a good living fixing wires and connections. These modules fill up with water sometimes, but he's in Arizona, I doubt it's wet.
I hope you got something cause I'm leaving work and when I log back on this board I'm gonna be lit.

 

[rovercanus]

I worked at a place that had massive dc drives from the early 80's. I'm talking 3 cabinets 4' wide by 6' high. Control voltage was usually 0-10 volts running through relays. Big clunky relays.
It doesn't take much degradation to mess a low voltage signal up. Ever have your cable service go sucky? Bad wiring and connectors can very much effect what your signal is. You don't need to live in a wet environment to degrade connectors or wiring.
But we still haven't heard what symptoms he's having.

 

[Injuhneer]

Symptoms I'm having? Other than the headache caused by my truck I am ok. Oh wait, you meant the truck. Ah, yes.

I referenced the symptoms over on the thread about the cam position sensor then closed that out and started over here.

I noticed rough, low idle intermittent. This is a new development. I happened to be watching the timing advance and such because the cam sensor mod had been adjusted. I noticed when the idle was slightly rough and low the data from the ECM went flatline on everythign except RPM, voltage, and engine temp.

O2 sensors, MAF, throttle position, everything but those three mentioned. When rough idle cleared (no misfires recorded) teh data all came back then I noted that the MAF is low as in less than 10 cfm (sorry, haven't switched/capitulated entirely to metric). Even at WOT mid-RPM range (3k) it never broke 20. This motor should be passing 230-250 cfm at that point.

Anywayz; symptomz - Rough idle concurrent with loss of data feed from ECM.

Yes, I have done this with the ELM327 and with a USB connected cable. Same behavior.

 

[Injuhneer]

well then riddle me this rovercanus.. How come nobody on this board ever thinks a wire or connection with excessive resistance is a possible cause? It's always gotta be the module if it wasn't the sensor. Am I being to logical? I almost never see a module fail anymore, but I make a good living fixing wires and connections. These modules fill up with water sometimes, but he's in Arizona, I doubt it's wet.
I hope you got something cause I'm leaving work and when I log back on this board I'm gonna be lit.

I always check wiring. Old habit from owning British roadsters years ago and Citroens more recently. The Fluke 87 is my friend.

Here in AZ wiring suffers from the heat and dryness. Insulation desiccates then cracks or crumbles.

 

[discostew]

If this is an advanced evaps truck, check the referance voltage at the tps when it's idling the way you describe and all data drops off. I know of a condition that will cause the referance voltage for that sensor drop to less than a volt at times. The fuel tank pressure sensor will short out and since it shares the referance voltage with the tps it causes all kinds of problems.
I'm sure you know better than me that Ohms law states that the voltage drop in a parallel circuit will be equal in all legs of the circuit.

 

[smrover1]

I know all about fuel pressure sensor short. It had my truck down for close to a year. Figured the whole problem out from a member on this board

 

[discostew]

I know all about fuel pressure sensor short. It had my truck down for close to a year. Figured the whole problem out from a member on this board

Ya I remember. I've seen it like 3 times, something you never forget once you experience it.

 

[Injuhneer]

Thanks. That points me in a direction. The ECM isn't much help when there are problems and it provides no codes. There were few codes for misfires when comms to the ECM came back. Other than that, nada.

I'll put the meter in the truck and drive until it does the thing. I'll also read up on threads here about the sensor short.

 

[discostew]

Always compare the the ground the ECM sees with actual ground ( the alternator case) when the engine is running. When you get strange stuff like your describing that should be a suspect. Another thing to consider is that all systems have a sensor that has to be just accepted as true. Like the MAP sensor on a GM system from the 90's say. When you turn the key on it gives a baro reading and when you start the car it's engine vacuum. The system really has no way of knowing that reading is incorrrect and it forces us to compare it to another like vehicle to get a clue that its not correct.

 

[Injuhneer]

Going out this AM to check it out. Oddly this only impacts idle. It runs fine otherwise.

 

[discostew]

If it's just a problem with the idle I would reset the learned closed throttle position, then set the min idle. Not sure how you guys without a T4 do that. With T4 the system monitors the IAC counts while you turn the idle air bleed to a target #. That doesn't really explain why your condition would come and go. I've learned over the years that most if not all intermittents are caused by poor connections.

 

[Injuhneer]

Always compare the the ground the ECM sees with actual ground ( the alternator case) when the engine is running. When you get strange stuff like your describing that should be a suspect. Another thing to consider is that all systems have a sensor that has to be just accepted as true. Like the MAP sensor on a GM system from the 90's say. When you turn the key on it gives a baro reading and when you start the car it's engine vacuum. The system really has no way of knowing that reading is incorrrect and it forces us to compare it to another like vehicle to get a clue that its not correct.

I did this several ways. Alt casing to ECM ground; no detectable voltage difference. Then engine to ECM power and chassis to ECM power. All normal. Engine ground is good. Chassis ground is good. ECM ground and power agree that all is well (as does the starter).

I did the static check on the TPS (per workshop manual) and found it to have one side intermittent open. Rotating the hub in the TPS toward the zero point held by the throttle shaft made the signal resistance climb then go open about where closed throttle would be.

I have a spare TPS. It checked out OK so I pulled the old and replaced it. On restart the idle immediately jumped to stupid mode (~1700 rpm) and won't return. Seems odd it would jump to limp-home mode on one try.

 

[Injuhneer]

If it's just a problem with the idle I would reset the learned closed throttle position, then set the min idle. Not sure how you guys without a T4 do that. With T4 the system monitors the IAC counts while you turn the idle air bleed to a target #. That doesn't really explain why your condition would come and go. I've learned over the years that most if not all intermittents are caused by poor connections.

While checking this chassis ground, engine ground, TPS, MAF, and IAC connectors have all be cleaned and treated with INOX. No obvious ground problems at this point.

 

[Injuhneer]

If it's just a problem with the idle I would reset the learned closed throttle position, then set the min idle. Not sure how you guys without a T4 do that. With T4 the system monitors the IAC counts while you turn the idle air bleed to a target #. That doesn't really explain why your condition would come and go. I've learned over the years that most if not all intermittents are caused by poor connections.

Yeah, how is it done without a testbook? Any known code readers that can do it? I have a K+D CAN cable. Any software that can do it?