Car Problem

[Mike Goetzke]

My daughter has a 2002 Pontiac Grand Am GT (125,000 miles). About 8 months ago it had a ck engine light with code P0131 (low sensor voltage). I checked the sensor with my scanner and sprayed carb cleaner into the intake and it had no reaction so I replaced it. Same thing happened 4 months later and sensor was bad. Now she got the code the third time and the sensor seems to be OK. She said the car will not move when you try to accelerate. I took it for a test and indeed found if I hard accelerated (pedal to metal) it seemed to misfire/backfire and if I let off the accelerator a bit it was fine. Now on another day of testing the car would not accelerate at all even at low speeds. It even seems to idle roughly.

I have a scanner that can record live data but I'm not a mechanic so don't know what to look for. From another forum I did record O2 sensor output and STFM LTFM (short & long term fuel map). The O2 sensor seems to be doing what it should. The LTFM is reading +15 to +20% meaning it is adding lots of fuel to make power. So as suggested I started looking at fuel system related things:

- I replaced the fuel pressure regulator
- replaced the fuel filter
- checked the fuel pressure (46psi key on, 40psi idle, and when accelerated jumps to 50psi and then back to 38psi)
- also checked catalytic converter temps like I saw online and it seems to be functioning
- my scanner has a CAT check too and it passes
- I took my old timing light out and on some cylinders I could see misfire at times

- I didn't do anything with the fuel injectors but how this seems to be very intermittent at soft accelerations I shying away from a fueling issue (maybe I'm wrong)

From reading online could be:

- crank sensor
- cam sensor

I'm now thinking this could be electrical related? I had a car years ago that was misfiring and it was the ignition control module.

Any help appreciated.


Thanks,

Mike

[Tom Stenzel]

Hi Mike,

Long distance diagnosing will be a problem.

I have a 2004 Chevy Venture with the 3.4 liter V-6 that had similar problems when accelerating. In my case the check engine light was on with a code that pointed to the O2 sensor upstream of the catalytic converter even though it had recently been replaced. It turned out to be the MAF (mass air flow) sensor. The air filter had collapsed and the little temp sensors were covered with dust.

The GM diagnostics don't always mark the sensor as bad and will use whatever nonsense it spits out. The easiest way to check it is to find the MAF electrical connector, disconnect it and give it a test drive. The check engine light will be on, the engine won't run quite right but see if it runs better.

The sensor uses what appears to be RTDs wrapped in nichrome wire, held in place by wires as fine as a thread. The MAF sensor cleaning spray is intended to remove oil films and won't take off dirt. If you go online you will read that they can't be physically touched or they will break. I was able to clean the sensors with a brush made from cut writing paper and a hemostat, then used the cleaning spray to physically remove the loosened dirt. It was try fixing it or replacing it so I gave it a go. It now runs fine even though my daughter hates my "ghetto" van.

If that's not it it could be wires, coil pack(s), thinking of the possibilities gives me a headache. The engine in general is painful to work on. Putting the thermostat housing UNDER the exhaust manifold? A company like that should go bankrupt.

Oh, wait...

-Tom

[Jeff Monson]

Misfire on light acceleration is normally ignition related. I didnt see where you stated the engine size, 2.2 or a 3.4?? The ck engine light may have nothing to do with the current problem. Seems you have a good handle on the fuel system so far. I'd look into the ignition system, let me know the engine size please.

[Mike Goetzke]

Tom - I'll look into the MAF sensor. A friend of mine says his car has a bulletin to periodically clean them.

[Mike Goetzke]

Misfire on light acceleration is normally ignition related. I didnt see where you stated the engine size, 2.2 or a 3.4?? The ck engine light may have nothing to do with the current problem. Seems you have a good handle on the fuel system so far. I'd look into the ignition system, let me know the engine size please.


Sorry - 3.4L

[Jeff Monson]

Well I'd do a ck of the plugs and wires. Do you know if they are original? A bog or hesitation may indicate rich or lean, but a misfire is usually cylinder specific. Under load is most certainly ignition. If the wires are original, 125k is a good life. The plugs were due at 100k.

[Mike Goetzke]

Hi Mike,

Long distance diagnosing will be a problem.

I have a 2004 Chevy Venture with the 3.4 liter V-6 that had similar problems when accelerating. In my case the check engine light was on with a code that pointed to the O2 sensor upstream of the catalytic converter even though it had recently been replaced. It turned out to be the MAF (mass air flow) sensor. The air filter had collapsed and the little temp sensors were covered with dust.

The GM diagnostics don't always mark the sensor as bad and will use whatever nonsense it spits out. The easiest way to check it is to find the MAF electrical connector, disconnect it and give it a test drive. The check engine light will be on, the engine won't run quite right but see if it runs better.

The sensor uses what appears to be RTDs wrapped in nichrome wire, held in place by wires as fine as a thread. The MAF sensor cleaning spray is intended to remove oil films and won't take off dirt. If you go online you will read that they can't be physically touched or they will break. I was able to clean the sensors with a brush made from cut writing paper and a hemostat, then used the cleaning spray to physically remove the loosened dirt. It was try fixing it or replacing it so I gave it a go. It now runs fine even though my daughter hates my "ghetto" van.

If that's not it it could be wires, coil pack(s), thinking of the possibilities gives me a headache. The engine in general is painful to work on. Putting the thermostat housing UNDER the exhaust manifold? A company like that should go bankrupt.

Oh, wait...

-Tom

E-U-R-E-K-A....unplugged the MAF sensor and it's a new car!

Guess I can buy one or try cleaning it.

Thanks,

Mike

[Gordon Eyre]

I long for the old days when I could fix anything on my car.

[Jim Koepke]

All this trouble with these new fangled cars has me thinking about my next vehicle being a '53 pickup.

jtk

[Jeff Monson]

Gotta like a simple fix. Good deal!!

[Bruce Wrenn]

Autozone can scan car, then take scanner to computer and almost always spot problem. Wife's 2006 Suzuki Grand Vitira check engine light comes on if gas cap isn't tightened. Also if battery is disconnected for more than 30 sec, you WILL CLEAN MAF sensor

[Tom Stenzel]

E-U-R-E-K-A....unplugged the MAF sensor and it's a new car!

Guess I can buy one or try cleaning it.

Thanks,

Mike

You won't thank me once you see how much one of those buggers cost! :eek:

Cleaning it isn't for the faint of heart. I used a 5X eye loupe to see what I was doing. Lotsa luck and be careful. You can only reach in from the downstream side, that's why I made a brush (curved tip hemostat) to reach around the wires and brush the RTDs on the far side.

Normally the problem with MAF sensors is oil vapor backing up the intake manifold and contaminating it. The sprays are pretty effective for that. In my case the heaters around the RTDs had melted whatever had gotten past the filter and the junk was really stuck.

If you put one of those high performance air cleaners that uses an oil-wetted element that can cause problems too. Plus void any warranty, the mechanics are quick to spot that.

-Tom

[Mike Goetzke]

You won't thank me once you see how much one of those buggers cost! :eek:

Cleaning it isn't for the faint of heart. I used a 5X eye loupe to see what I was doing. Lotsa luck and be careful. You can only reach in from the downstream side, that's why I made a brush (curved tip hemostat) to reach around the wires and brush the RTDs on the far side.

Normally the problem with MAF sensors is oil vapor backing up the intake manifold and contaminating it. The sprays are pretty effective for that. In my case the heaters around the RTDs had melted whatever had gotten past the filter and the junk was really stuck.

If you put one of those high performance air cleaners that uses an oil-wetted element that can cause problems too. Plus void any warranty, the mechanics are quick to spot that.

-Tom

I put the magnifiers on and actually the fine wires looked clean. I used the special cleaner on them anyway. Didn't help. Ended up picking up a new one for around $70 after discounts/coupons. Car runs like new again. Once again thanks for your help!


Mike

[Wayne Lomman]

Gordon/Jim, I'm with you. I have an '86 Range Rover and thought I would upgrade to a '97 model. I hate it - way too technical. Fortunately I bought it cheap. Sold it today and I will keep the old one. Cheers.