FAQ: Mass Air Flow (MAF) Sensor Issues?

also did you recheck the nylon fuel lines underhood for leaks/splits?

and also did you get a code reader to tell you what SES code was set?

Will check the above when we get there tomorrow, albert. I was thinking of also checking the IAC. Although, it makes sense that a clogged cat could cause the O2 sensor to throw a code and the black smoke. The car runs without a symptom on level ground and in an instant, it died going downhill.

Edit: Doing some research online, A few folks are saying that a clogged filter might cause this.

I vote for ISC or TPS or MAF...
Why would a clogged cat manifest going downhill, in the lowest exhaust pressure scenario?

Well, we got the car started. We just gave it a shot and she tuned over. While it was running we retrieved a code which was a P0102 MAF circuit code. The car ran for about ten minutes and then stalled, so the mechanic unplugged the MAF sensor and said that if you leave it unplugged it goes into a failsafe mode and it will get you where you need to go, but not to rely on it as drive-ability issues will arise. So the dealer wanted $440 bucks for the sensor not including installation. So we said we would think about it and took the car home. We bought an aftermarket MAF sensor for $160 and installed it ourselves. The car started up, we went for a drive and then shut the car off. We started it up again and the SES light turned off. We went and did some grocery shopping and when we returned to the car, we started it up and it stalled. Started it up again and it stalled, so we unplugged it to get home. When we got the car home we shut it off, plugged the MAF back in and tried starting it and it did without stalling. So the MAF may have set a code but the stalling issue is elsewhere. Its definately not the FP, so Aaron feel free to move this where you feel its more appropriate.

Oh and we removed the IAC and PCV valve and cleaned them.

Car won't start at all now, and the SES light has recorded a P0300, random misfire code? Any thoughts?

Edit: I should mention that my Dads car has needed recharging after he drained it trying to start it on the weekend, and its old. Could a weak battery cause this?

BMD wrote:

Car won't start at all now, and the SES light has recorded a P0300, random misfire code? Any thoughts?

Edit: I should mention that my Dads car has needed recharging after he drained it trying to start it on the weekend, and its old. Could a weak battery cause this?

As for your edit, yeah. Need to load test the battery when charged and find out what capacity it has (how many CCAs). It can start the car but it capacity is low other weird stuff happens (ask me how I know )

As for your misfire I wonder if there is a problem in the wire harness between the firewall and the ignition module. Remember those threads from various posters about the wires in teh corners fo the connectors corroding/breaking? Just sayin.'

What else have you eliminated - what else do you think might be up?

Albert

Thanks for the response albert. My Dad said that the spark plugs were replaced a couple of years ago as was the fuel and air filter, wires look original though. The middle coil pack looks a little corrosive, should we take that off and check it underneath? What about the EGR valve, can that be removed and cleaned. We cleaned the PCV valve and seat with Intake cleaner and now my Dad thinks that that is the culprit. Also, he said that he filled up the night before all his problems began, could bad fuel be causing this?

BMD wrote:

Thanks for the response albert. My Dad said that the spark plugs were replaced a couple of years ago as was the fuel and air filter, wires look original though. The middle coil pack looks a little corrosive, should we take that off and check it underneath? What about the EGR valve, can that be removed and cleaned. We cleaned the PCV valve and seat with Intake cleaner and now my Dad thinks that that is the culprit. Also, he said that he filled up the night before all his problems began, could bad fuel be causing this?

Bad fuel could be a problem but you'd know better than I'd know.

As for coil packs, taking them off and cleaning the ignition module is a great idea - not sure it will fix the problem but it will eliminate issues. And I had a bad wire (my OE #6 wire) take out a coil. If the wires are sketchy at all based on my experience I'd replace 'em.

The EGR can be removed and cleaned, GM dealers sell a very good EGR cleaner, maybe someone else on here has the P/N. I think you'll want to get a gasket or 2 from NAPA or some such before you pull the EGR.

I have not had PCV problems worth beans since I drove a '68 Dodge Dart.

Your problem bugs me. It does not match the patterns of failure I have seen in the past. I can and am answering your questions but actually I am stumped at this point except for fixing the obvious (wires, remove corrosion and replace that coil, check and perhaps replace battery) and making sure I was caught up on maintenance (what is in the air box besides air cleaner?)

So, if you keep the MAF unplugged it runs without stalling? All these "issues" arise when it's plugged in?

Yes, the car would start and then stall with the new ( or old ) MAF sensor plugged in, but now, wether its plugged in or not, the car won't start period. There is fuel getting to the rail cause it squirted out of the valve while trying to start. We cleaned the coil packs and plug boots at the coil pack end. We removed and cleaned the EGR valve, spark plugs look textbook dry and plenty of electrode. I'm thinking its either a bad coil or fuel injectors or a weird electrical issue.

Edit: So check this out, The C31 10A ( or IGN fuse) keeps blowing!?!

Is that all it says on the lid is IGN fuse? I can't find that specific fuse in the Power Distribution schematic. Is this fuse in the Interior or under the hood?

I wonder if it's the 10A RUN fuse. That fuse is directly connected to the Ignition Switch.

The fuse is under the hood and on the fuse cap sticker it says C13 10A. Remember, this is my Dads 99 supercharged PA.

BMD wrote:

Yes, the car would start and then stall with the new ( or old ) MAF sensor plugged in, but now, wether its plugged in or not, the car won't start period. There is fuel getting to the rail cause it squirted out of the valve while trying to start. We cleaned the coil packs and plug boots at the coil pack end. We removed and cleaned the EGR valve, spark plugs look textbook dry and plenty of electrode. I'm thinking its either a bad coil or fuel injectors or a weird electrical issue.

Edit: So check this out, The C31 10A ( or IGN fuse) keeps blowing!?!

Some time ago I had a bad spark plug wire (#6, the center conductor broke off the spark plug terminal, jacket stayed intact) and it took out a coil. Car ran - but the SES light came on and it ran somewhat weakly. So I wonder if the corrosion might have messed up your coil. Somewhere else on this site someone already posted the values you should get if you measure a coil with an ohmmeter. Even so if you measure all 3 coils and 2 are the same and one is off I'd replace the one.



With that IGN fuse blowing I wonder if the ign module is wack because of the misfiring coil. If so then you need a coil and a module.

BMD wrote:

The fuse is under the hood and on the fuse cap sticker it says C13 10A. Remember, this is my Dads 99 supercharged PA.

I know. That's what I looked up.

albertj wrote:

With that IGN fuse blowing I wonder if the ign module is wack because of the misfiring coil. If so then you need a coil and a module.

Where is the IGN module usually located?

BMD wrote:

albertj wrote:

With that IGN fuse blowing I wonder if the ign module is wack because of the misfiring coil. If so then you need a coil and a module.

Where is the IGN module usually located?

Beneath the coils.

BMD wrote:

albertj wrote:

With that IGN fuse blowing I wonder if the ign module is wack because of the misfiring coil. If so then you need a coil and a module.

Where is the IGN module usually located?

IM is under the coils.

If you pull the coils to fuss with the ignition module be sure to clean it off and put dielectric or heat sink grease on it when reassembling. Just a dollop in the middle of the metal plate on teh bottom of the module so it will spread to the edges from there and push the air out with it. Radio Shack #2102858, it's a small tube you'll use all of it. Tune up grease will work too. By the way the RadioShack grease is great for putting between the heat sink and the surface of your computer's CPU if you take it apart for celaning or upgrade...

If you *don't* use a heat transfer grease on the ignition module it will cook itself. I kinda wonder if that's what's wrong with the several ignition-related problems that have been posted lately, that and maybe mis-gapped plugs (the plug gap has to be 0.060 spot on).

Well, we know that the IGN fuse blows up just by putting the key in the ON position and not even trying to start the car. We looked for damaged wires with no luck. I thought it might be perhaps the Ignition switch causing this, but I couldn't figure out how to separate the top and bottom half of the steering column cover, it looks you might have to remove the steering wheel before you can remove the cover. Weather is def. not co-operating so my Dad is calling it quits, hes calling a tow-truck on Monday.

So the shop found that indeed it was the Ignition Module that was fried. They swapped it out and now it starts every time, but, right after it starts up the idle goes to about 1000 then drops to about 200 and wants to die, then picks up on its own and goes back up and then runs perfect. We already switched the MAF sensor when we got that code and we just changed the IAC valve to no avail. Any ideas?, should we go ahead and change the TPS now?

BMD wrote:

So the shop found that indeed it was the Ignition Module that was fried. They swapped it out and now it starts every time, but, right after it starts up the idle goes to about 1000 then drops to about 200 and wants to die, then picks up on its own and goes back up and then runs perfect. We already switched the MAF sensor when we got that code and we just changed the IAC valve to no avail. Any ideas?, should we go ahead and change the TPS now?

do you think the throttle body is clean? Dirty throttle body will make the idle "hunt" warm or cold. More noticeable warm though.

do you think the temp sensor is working properly?

do you have service records that tell what was replaced before you got the car (maybe there is a smoking gun so to speak)?

I am stumped, at this point I'd have the car connected to Car-code and be plotting the output of the tps and other sensors to see which one was slow...

if this car had a carburetor I'd recalibrate or replace the automatic choke.

what do you think?

Albertj

Hey albert, well I know it never had a carb on it 'cause its 99 PA . He bought it with 70K on it eight years ago. The temp sensor is less than a year old, so I don't think thats it. Dirty throttle body might be a possibility, will definitely look into that. Thanks again for your input.

BMD wrote:

Hey albert, well I know it never had a carb on it 'cause its 99 PA . He bought it with 70K on it eight years ago. The temp sensor is less than a year old, so I don't think thats it. Dirty throttle body might be a possibility, will definitely look into that. Thanks again for your input.

lemme clear that up... it's not that it ever had a carb on it. Rather that the behavior you're talking about, if it occurred on a carbureted car, would always be that problem - the auto choke not reacting properly to temperature.

On cars such as ours the most you can narrow it down to without testing and pulling things is the whatever controls the air/gas mix at cold idle. Could be temp sensor, could be throttle body, could be etcetera. Sorry fo r the confusion, I was thinking out loud and it's late. G'night!

Albertj

albertj wrote:

lemme clear that up... it's not that it ever had a carb on it. Rather that the behavior you're talking about, if it occurred on a carbureted car, would always be that problem - the auto choke not reacting properly to temperature.

Yeah, thats my bad albert, I shoulda understood that it was reference only.

Well, we have since cleaned the throttle body, it was coated with black soot, and the throttle plate was sticking slightly. We have also put in a new Throttle Position Sensor to go along with the new Idle Air Control Valve and Mass Air Flow sensor, PCV valve and Coolant Temperature Sensor. We also changed the fuel filter and air filter. There is tons of fuel pressure and the car always starts on a dime. Infact during the first (cold) start of the day, it starts perfect. Every subsequent start, the car starts then wants to stall, especially when its warm. But with a little help from the gas pedal, it stays running and then operates great, no stumbles at all, until you shut the car off and then try a re-start. Could it be a bad fuel regulator? If you have any ideas, just throw 'em out.

Also we tor apart the bad ignition module to see whats inside, so here ya go...

It Cheetoed on you... fried to a crackly crunch.

I have been told this is what happens if they are mis-installed. Mis-installed means no/not enough heat sink grease on re-assembly and/or missing insulator.

What did you find when you pulled it? no grease?

And as for your bad warm start problem, do you think you might want to check for corrosion on the connectors to the IAC, MAF and TPS (unlikely) ? I would also double check the reinstalled TB for air leaks at the gasket, a small leak can miss things up big time... and if you reused the TB gasket you might want to get new one. I am guessing your issue is in or in vicinity of the TB and I'd check the air filter, hold it up to a strong light and check it. Knock out the loose dust and check again, if it's still pretty dark in the pleats replace...

Albertj

Hey albert, thanks for the response. Just so I'm clear, those frayed looking wires on the old IGN module were connected, we had to pry the two pieces apart with some effort. It just looks that way now because we ripped it apart.

As for the warm start issue, it was there before we took the Throttle Body off, we just decided to clean it, thinking it might help. We also use a new gasket and a new air filter. As far as corrosion at the connectors, there is none to be had, but just in case, we used electrical cleaner on them. What about my Fuel Pressure Regulator guess?

BMD wrote:

As for the warm start issue, it was there before we took the Throttle Body off, we just decided to clean it, thinking it might help. We also use a new gasket and a new air filter. As far as corrosion at the connectors, there is none to be had, but just in case, we used electrical cleaner on them. What about my Fuel Pressure Regulator guess?

I see that you've covered all the usual suspects but one - have you checked for a 'classic' vacuum line leak? On an open-loop cold start, there's enough enrichment to handle a small vacuum leak; a warm start is leaner... Have you checked all the vacuum hoses with eyeballs and spritzes of carb-cleaner?

As far as the pressure-regulator goes, how many PSI are there in a 'ton' of fuel pressure?

Eldo wrote:

As far as the pressure-regulator goes, how many PSI are there in a 'ton' of fuel pressure?

I believe a "ton" of psi's are nothing but a plethora of single psi's, therefore, enough to run the car