2G Misfiring! *Reward*

[gma0408]

First of all, I would like to say that I have been searching and reading up on anything that might help me fix my problem. I've been working (on and off) trying to solve this for the last 3 months!

So it's come to this: If someone helps me find or leads me to the solution of my misfiring, I'll either pay them or give them a part off of my car...cop, new 1G TB, etc. I haven't really decided yet.

If you guys can't solve it, I'm taking it to a shop. You guys are my last resort.


It all started when I drove my car home...in the rain...if that means anything. The car ran like a champ up until i got to the garage. It started misfiring....throughout the entire rpm. Well up until about 4k, because it'll bog if I try to take it higher. The exhaust smells like the car is putting out too much gas. When I try and drive the car, it jerks....its the same feeling it had when my positive battery connector was loose a while back.

I do have DSMlink, but I'm not really familiar with it yet. I just got the car up and running this spring after having done a 6 bolt swap.

The car is showing no cels.

Things that I have changed out....

-cam angle sensor
-COP...for stock coils and wires
-Power Transistor
-Spark plugs... new bpr7es with the correct gap
-ECU...tested in a friends car
-2 relays behind radio
-Gold box ...MFI relay?
-GM MAF
-Map sensor

Things that I have checked...

-boost leaks...slight one at bov, but fixed it and no change
-timing
-Compression is perfect...motor is nearly new
-grounds...cleaned up ALL connections/terminals
-injectors...new, but checked anyway
-battery...new, but checked
-Alternator... putting out 13.9 volts
-Fuel pump is working and fuel regulator gauge shows constant pressure
-ISC..coils are good
-Undid turbo timer and boost controller

The only things I have not changed out yet are the MAF Translator...which when unplugged the car will actually idle better, the injector resistor pack on the firewall, and the engine harness.

PLEASE HELP! Any ideas or thoughts would be appreciated.

 

[grnchevyz]

I'd check the MAF itself...if water got to it it could have fouled the sensor inside it. I know I had that issue on my GSX and once I changed the MAF no more misfiring.

 

[donmagicjuan]

gma0408,

This could very well be a MAS signal issue, especially since you say the car runs better with the translator disconnected. Do you have a wideband or AFR gage to enable you to post the AFRs you're seeing during all of this? Also, could you post the MAS frequency that you observe? Finally, is all of this information based on revving the car in neutral, or are you able to drive the car?

If you have the means, I would recommend reconnecting the stock MAS and seeing what happens. Let us know if you have anymore information.

 

[danyz250f]

Well I am not really sure on your mods like all of them you have done.

But Misfires with a 6 bolt swap are a common thing and it is good you have link. I think you can invert the CAS sensor in dsm link and that usually gets rid of the misfire. I think in theory. I have a 1g not first hand experience. But you do have to swap and go to a 1g cas I believe.

Other than that.

Sometimes a rocker arm will fall off a valve and cause sputtering.

Of course boost leaks are the main problem of boost leaks

Plugs wires.

those are my suggestion

 

[gma0408]

I'd check the MAF itself...if water got to it it could have fouled the sensor inside it. I know I had that issue on my GSX and once I changed the MAF no more misfiring.

The maf was changed out for a known good one.

,

This could very well be a MAS signal issue, especially since you say the car runs better with the translator disconnected. Do you have a wideband or AFR gage to enable you to post the AFRs you're seeing during all of this? Also, could you post the MAS frequency that you observe? Finally, is all of this information based on revving the car in neutral, or are you able to drive the car?

If you have the means, I would recommend reconnecting the stock MAS and seeing what happens. Let us know if you have anymore information.

Well, it certainly is a lot smoother. The idle will jumped from 1200 to 1500 and it'll blurp every coupld of seconds, but it does hold steady. The blurp could be because of the 272's and I just haven't heard them in a while. It won't let me rev past more than 2k.

Now that you mention it, the air/fuel reading on my laptop is showing LEAN....it stays at a constant 18:1, which is the highest it'll go... where as when it ran fine was 15:1.

I'm not sure how to find out the mas frequency???

All this is based on revving...when i try to drive the car, it jerks as if I had a gigantic boost leak...then it'll pop when i get to 4k.

Well I am not really sure on your mods like all of them you have done.

But Misfires with a 6 bolt swap are a common thing and it is good you have link. I think you can invert the CAS sensor in dsm link and that usually gets rid of the misfire. I think in theory. I have a 1g not first hand experience. But you do have to swap and go to a 1g cas I believe.

Other than that.

Sometimes a rocker arm will fall off a valve and cause sputtering.

Of course boost leaks are the main problem of boost leaks

Plugs wires.

those are my suggestion

The cas is inverted.

I Will check the rocker arms though and the last thing I did change on the car was the timing belt.

 

[donmagicjuan]

I'm not sure how to find out the mas frequency???

Sorry, every once in a while I forget that not everyone has this ability (it's an ECU+ capability).

At this point, since you have adequate fuel pressure, I'd lean toward a faulty MAF-T or a wiring fault that's preventing the ECU from getting a MAS signal. This would explain the lean condition and your inability to attain engine speeds of over 4k RPM. I'm guessing you don't have another one of those lying around to swap with the original one, which is why I suggested plugging in the stock MAS again. I realize though that you might not be able to do that either.

Is there any way for you to retrieve an airflow signal to analyze (e.g. lb/min)? Looking at what that's doing as you rev the engine will help with the diagnosis.

Good luck.

 

[gma0408]

I'm going to try and find a 2g maf...

Ill see if i can find the airflow signal

Ill check back in tomorrow.

 

[gma0408]

I checked on DSM Link for the air flow and it came out as follows:

1500 rpm
air flow per rev= 0.37 g/rev
air flow = 9.2 gm/sec

3500 rpm
air flow per rev = 0.45 g/rev
air flow = 25.7 gm/sec

For about the first 10 seconds the air fuel is 15:1 then after that goes to 18:1 at idle and stays that way.

 

[donmagicjuan]

I'm not very used to seeing those numbers, but at least it looks as though the signal is getting to the ECU. Is your AFR based off of the stock front narrowband or a wideband O2 sensor? If it's the front one, my next check would be the O2 sensor. When they fail they peg lean. The first few seconds that you're seeing 15:1 are not really relevant, because the reading will not be accurate until the heater has warmed it up to operating temperature.

 

[gma0408]

I'm not very used to seeing those numbers, but at least it looks as though the signal is getting to the ECU. Is your AFR based off of the stock front narrowband or a wideband O2 sensor? If it's the front one, my next check would be the O2 sensor. When they fail they peg lean. The first few seconds that you're seeing 15:1 are not really relevant, because the reading will not be accurate until the heater has warmed it up to operating temperature.

So, you don't think it's the translator?

Yes, the AFR is based off of the front o2 sensor. Is there a way to check this?

Someone also mentioned my fpr might be faulty. I'll change that out and let you know.

I did swap injector resistor packs with no success.

 

[donmagicjuan]

As I said, I'm not familiar with those airflow units, so I can't really confirm the MAF-T is translating properly, but you're seeing a signal that positively correlates to real airflow, which is a good sign.

If your O2 sensor fails lean, the car will continue to add fuel in an attempt to bring the value down to the correct ratio whenever it's in closed loop. This being the case, you would actually be running extremely rich rather than lean.

Without knowing your true AFR, it's impossible for me to say conclusively whether it's a failed O2 sensor or a fuel volume issue, but I would say that it is much more common for a O2 sensor to fail than a fuel pressure regulator. The check for the sensor usually involves measuring the voltage across it with the car running, which you already know to be bad.

 

[danyz250f]

More food for thought, is the cas timed right? Do the marks line up?

 

[92awddsm]

First and foremost, fill out your vehicle profile. At the moment, all I know is that you have a 2g with a 6 bolt. Is it 97-99 with a 95 eprom or is it a 95-96? This will make a difference in the plug wire order, ect.

The o2 sensor will only cause a problem at idle or part throttle. When you reach wot, the ecu goes into open loop and no longer relies on o2 readings for fuel requirements.

Check the coolant temp sensor and wiring, replace fuel filter, check tps, and drain the fuel and replace with fresh. I have seen fresh fuel contain large amounts of water that acted the same as you are talking about.

 

[AWDtsi1995]

Have you tried this:

This fix will keep the ECU from looking for misfires at all. This is the criterion that must be met before the ECU will start to look for misfires:
· 300+ seconds of steady state RPM less than 80% throttle position
· Engine coolant temperature -10C or higher
· Intake air temperature -10C or higher
· Barometric pressure greater than 76 kPa
Now if we can get one of these values outside of the criteria the ECU won't check for misfires. The value that would be the easiest to change would be the barometric pressure sensor. We're going to add resistance to this value so that the ECU will see less barometric pressure than what there really is. This will also lean the car out so you should see a performance increase as well. Depending on the car and altitude you might need
to add more fuel with an AFC.

So let's get started, Parts needed:
· A 10K potentiometer (although a 5K would probably do just fine). These are available at any
electronics store, if you go to Radio Shack ask for a volume control knob because they don't know
what a potentiometer is.
· Wire strippers
· Soldering iron

Step 1: Remove the access panel on the driver's side of the center console. You should now see four plugs with a ton of wires going to them.

Step 2: Pull out the top plug, it'll be the one that's the hardest to reach. Locate wire #85. It's orange with a white stripe.

Step 3: Cut the orange wire in half. Solder one end of the wire to the center peg of your potentiometer. Solder the other end to either the left or right leg, it doesn't matter which. Turn your potentiometer all the way counter-clockwise.

Step 4: Plug the harness back in and start up the car. It should sound like it did before you did any modifications. If the idle is choppy or the car won't run you turned your potentiometer the wrong way.

Step 5: Add resistance to the barometric pressure sensor by slowly turning the knob on the potentiometer.

Drive the car around; if you get a CEL then add some more resistance. Keep doing this until you no longer get
the CELs.


EDIT: Sorry after reading your post again i saw that you said you are getting no CELs so this might not work.

 

[92awddsm]

Have you tried this:

This fix will keep the ECU from looking for misfires at all. This is the criterion that must be met before the ECU will start to look for misfires:
· 300+ seconds of steady state RPM less than 80% throttle position
· Engine coolant temperature -10C or higher
· Intake air temperature -10C or higher
· Barometric pressure greater than 76 kPa
Now if we can get one of these values outside of the criteria the ECU won’t check for misfires. The value that would be the easiest to change would be the barometric pressure sensor. We’re going to add resistance to this value so that the ECU will see less barometric pressure than what there really is. This will also lean the car out so you should see a performance increase as well. Depending on the car and altitude you might need
to add more fuel with an AFC.

So let’s get started, Parts needed:
· A 10K potentiometer (although a 5K would probably do just fine). These are available at any
electronics store, if you go to Radio Shack ask for a volume control knob because they don’t know
what a potentiometer is.
· Wire strippers
· Soldering iron

Step 1: Remove the access panel on the driver’s side of the center console. You should now see four plugs with a ton of wires going to them.

Step 2: Pull out the top plug, it’ll be the one that’s the hardest to reach. Locate wire #85. It’s orange with a white stripe.

Step 3: Cut the orange wire in half. Solder one end of the wire to the center peg of your potentiometer. Solder the other end to either the left or right leg, it doesn’t matter which. Turn your potentiometer all the way counter-clockwise.

Step 4: Plug the harness back in and start up the car. It should sound like it did before you did any modifications. If the idle is choppy or the car won’t run you turned your potentiometer the wrong way.

Step 5: Add resistance to the barometric pressure sensor by slowly turning the knob on the potentiometer.

Drive the car around; if you get a CEL then add some more resistance. Keep doing this until you no longer get
the CELs.


EDIT: Sorry after reading your post again i saw that you said you are getting no CELs so this might not work.

He also has dsm link so the potentiometer(rheostat) mod is not needed.

 

[gma0408]

First and foremost, fill out your vehicle profile. At the moment, all I know is that you have a 2g with a 6 bolt. Is it 97-99 with a 95 eprom or is it a 95-96? This will make a difference in the plug wire order, ect.

The o2 sensor will only cause a problem at idle or part throttle. When you reach wot, the ecu goes into open loop and no longer relies on o2 readings for fuel requirements.

Check the coolant temp sensor and wiring, replace fuel filter, check tps, and drain the fuel and replace with fresh. I have seen fresh fuel contain large amounts of water that acted the same as you are talking about.

Ok, I filled out the vehicle profile.

I also checked what the o2 was reading on dsmlink and its moving from 0.2 to 0.9. This is at about 1200 to 1500 RPM. I switched out the Fuel pressure regulator back to the stock one and it didn't do anything.

How do I check the coolant temp sensor?...but the wiring was checked.

The fuel filter is new, the tps was switched out and I replaced the fuel and also added in Seafoam.

The car is also timed right and the cas is in the right spot.

I should also mention that the car idles much worse than it did when it started a few months ago.

 

[92awddsm]

Ok, I filled out the vehicle profile.

I also checked what the o2 was reading on dsmlink and its moving from 0.2 to 0.9. This is at about 1200 to 1500 RPM. I switched out the Fuel pressure regulator back to the stock one and it didn't do anything.

How do I check the coolant temp sensor?...but the wiring was checked.

The fuel filter is new, the tps was switched out and I replaced the fuel and also added in Seafoam.

The car is also timed right and the cas is in the right spot.

I should also mention that the car idles much worse than it did when it started a few months ago.

Do you have the link setup properly for the 1600cc injectors? Even if you do, dont expect it to ever idle clean with them. I would go back and recheck injector setup and deadtime. Better yet, I would scrap the 1600's and install 1000's just to get away from the bad driving characteristics of the 1600's.

 

[donmagicjuan]

I think you guys are missing that the car went from functioning properly to exhibiting this problem without any changes to the engine. This would eliminate things such as injector size, plug wire order, etc. You have to narrow the scope to things that can suddenly fail. The reason I suggested an O2 sensor was because once the problem evidenced itself, the OP probably never attempted any WOT runs for fear that he would damage something.

To the OP, where does your AFR for DSMlink come from? I would expect with a failing O2 sensor that the faulty one would read lean and the working one would read rich (if the faulty one was the front one). The fact that the DSMlink voltage is fluctuating normally while the front one is pegged lean has me very puzzled.

 

[grnchevyz]

If you can, please amuse me and try the following...

If you can, remove the MAF-T and translator setup and revert back to a KNOWN WORKING 2g MAF. I know it may take a little bit but give it a try...if it goes away as both myself and donmagicjuan suggested a faulty MAF or translator, then you know where to put your energy

It seems it's the only missing link in the scenario..I know you said you replaced it with a known working one but if the translator is the problem, changing MAF 343672893492 times will still give you the same problem. Only by removing it from the equation all together or getting a known working GMAF and Translator setup and swapping it with yours will tell you if its something else.

As donmagicjuan said, I too am stumped on the DSMlink readings so lets make sure the other AFR "controller" for lack of a better word, is %100 good or bad.

Let us know!

 

[Defiant]

I should also mention that the car idles much worse than it did when it started a few months ago.

Have you checked the cam timing?

 

[tom04841]

My 1g did this occasionally. It turned out to be the power transistor was going. replaced it and problem is gone

 

[chetvram]

Have you checked your spark plug wires yet? I was getting bad misfire from a burnt wire arcing in the engine bay.

 

[danyz250f]

One way to check if you have a bad gm maf is to hit it with a piece of wood or rubber malet on the side while the car is running. If the idle changes then you might have a bad sensor. But if your car idle changes any ways then that method might not work.

My car ran super crappy once and it pissed me off alot and after many post and hours trying things it was the stock 1g mas.

Put in gm sensor and maft it fixed it.

Another time I was just running really rich.

It took me a acouple weeks to figure that out.

My friends car ran really crapy for like 6 months and it turned out to be the ### auto lite spark plugs. BPR6ES ngk and problem fixed.

 

[gma0408]

I checked the timing numerous times, being that the belt was the last thing done to the car. But it is fine.

I don't know why the a/f is showing up weird on the link. All the numbers are inserted correctly.

I really think its the translator as well. It's the only thing left I haven't changed out.

DOES ANYONE HAVE A 2G MAF THEY"LL LET ME BORROW?

 

[donmagicjuan]

I'm assuming that the AFR showing lean is on an AFR gage, which you said comes from the front O2 sensor voltage. Does the O2 voltage displayed in DSMlink come from the same source or somewhere else?
(Sorry, but I'm DSMlink retarded.)