vehicle : chevy Express Van 4500 cutaway
engine : L96 6.0L gasoline
situation : while doing engine dyno for vehicle emission test
DTC when this happened : P0174(Fuel System Too Lean (Bank 2)) - P0151(HO2S Circuit Low Voltage Bank 2 Sensor 1) - P0157(HO2S Circuit Low Voltage Bank 2 Sensor 2)
Hello,
While trying to do the engine dyno test for vehicle emission test we had the three DTC above. And we noticed that all of the ignition line (ignition plugs) of bank 2 weren't working. There was no spark at all on all of the Bank2 side(the engine was running). But when we did the O2sensor relearn while the engine was running suddenly all of the bank2 ignition plugs started to work correctly again.
Questions:
1_ Can the ignition plugs shut down because of the three codes I have mentioned?
2_ If yes which code is the main reason?
3_ And by my really small knowledge and common sense isn't the fuel system who has to shut down if there is a problem and not the ignition line(ignition plugs)? [This part is totally a noob thinking]
please help me find the reason why the Bank 2 ingnition line(ignition plugs) has shut down.
Thank you.
The coil banks are powered separately. 1,3,5,7 on one fuse, 2,4,6,8 on another. You probably have a bad connection somewhere between the power supply relays and the coils. Check the underside of the relay box for something loose.
The fuel injectors and ignition coils on each bank are powered by the same fuse, too. Probably so that losing the ignition system would not send raw fuel into the engine and out the exhaust.
Streetwiseguy said:
The coil banks are powered separately. 1,3,5,7 on one fuse, 2,4,6,8 on another. You probably have a bad connection somewhere between the power supply relays and the coils. Check the underside of the relay box for something loose.
Thank's.
We have checked fuses connections and all but there was no problem.
I heard that all GM engines have a RPM limiter that cuts off fuel and sometimes spark if the engine is over-reved- say above 4000 RPM.
I knew for the fuel cut off but not sure for the ignition plugs.
So I was wondering if my vehicle has the both cut off system for fuel and spark.
If yes when the cut off happens does it only cut off the Bank 2?
And I also heard that there is RPM limiter at 4000rpm at P/N position.
Is there any other RPM limiter except for the one I have mentioned?
Pete. (l33t FS) said:
The fuel injectors and ignition coils on each bank are powered by the same fuse, too. Probably so that losing the ignition system would not send raw fuel into the engine and out the exhaust.
Thank's. So if I understood correctly if there was a fuse problem fuel and spark wouldn't work. So it's probably not a fuse problem because the fuel worked. Am I correct?
I also think it wasn't a fuse problem because we checked but there was no blown fuses.
I heard that all GM engines have a RPM limiter that cuts off fuel and sometimes spark if the engine is over-reved- say above 4000 RPM.
I knew for the fuel cut off but not sure for the ignition plugs.
So I was wondering if my vehicle has the both cut off system for fuel and spark.
If yes when the cut off happens does it only cut off the Bank 2?
And I also heard that there is RPM limiter at 4000rpm at P/N position.
Is there any other RPM limiter except for the one I have mentioned?
Not being a GM calibrator, I would still guess that there are more than one engine speed limiter. It's not likely to be below 4000rpm, though- no reason for that. Unless you are trying to run the crap out of the engine, though, the speed limiters would not be interacting with the system. And even if they were, the system is smart enough to ignore a lean bank in that time.
In another post, you mentioned going down the HP tuners path. That is capable of taking data- and a lot of it. That will tell you a lot more than just the DTC's, and should give you an idea why the fuel is off on the one bank. And I would focus more on the fuel than the spark.
BTW, how are you determining that the spark is being turned off? Using a plug shorted to the block?
Anyway, take data recording the problem, and start looking at that. There's going to be a LOT of it, and learning what you are looking at will go a long way to understanding the testing you are going to be doing. And doing engine only emissions testing is a real pain in the rear- that's tried constantly, but it's never the same as a powertrain dyno, which isn't actually the same as a full chassis test.
Rev limiters cut fuel, never spark, so I triple doubt that it is a limiter.
The fuse comment is not so much "check the fuse" as "check the wiring". Have seen a few bad pins in OE fuseboxes that lasted right until the box was moved for other service.
Pete. (l33t FS) said:
Rev limiters cut fuel, never spark, so I triple doubt that it is a limiter.
The fuse comment is not so much "check the fuse" as "check the wiring". Have seen a few bad pins in OE fuseboxes that lasted right until the box was moved for other service.
Pete is right. When everything works as it should you should 12v+ at the coils and injectors all the time with the key on. If I were in your shoes I would start by finding out which wire is supposed to be 12v+, back probe it, hook up a graphing multimeter (I don't like using a test light where the pcm is involved) turn the key on and see if you have voltage, then start grabbing the wire harness in various places and moving it around. I bet you see your voltage disappear as you get close to where the open is happening. Like Pete says, I have seen problems in the fuse boxes where the wire is terminated. I've also seen problems where people "tap in" to fuse terminals to add a circuit for something, it stretches out the female terminal causing a loose connection.
To answer your original post, no, those codes won't cause you to lose spark or fuel. But I bet it's the other way around, your electrical problem is causing the codes.
BTW, taking data will show you that the ECU is either trying to deliver the injection/spark or not. If it is, then the electrical issues that are being pointed out are very real. If the ECU is preventing the fuel/spark, then you need to figure out why that is happening.
Either way, take data, and you will have a lot more info to go on.
