hesitates, jurks or stops at times when slowing or stoping or starting out

[rcweston]

98 lumina 3.8
At times, the engine will miss and then hit causing a jumping or stuttering of the engine. Sometimes it will completely stop. Usually just a couple little jolts then things are fine again.
This occurs usually when accelerating from a stop, or when you have stopped accelerating and are putting on the break. Once in a while it will shut off while going down the freeway. That is bad and dangerous!
This happens to my son and wife often, but is hasn't ever happened to me, only a stutter when taking off once, so this info is the best I have.
I am wondering if this could be an electrical problem with the throttle position sensor. As I looked at the throttle, their is a cable from the gas pedal to the carburetor. I was thinking that it would just be some sort of sensor at the gas pedal that connected to the control module.
If someone has any ideas of what is going on, or if some one can explain in detail how the gas pedal system works, were the parts are located, and what to test , I would greatly appreciate it.
Thanks Rex
next day
I got a p0102 code today. MAF low signal in my simple book

[Blue Bowtie]

The accelerator is connected to the throttle bellcrank via a regular, old cable (mechanical). On the underside of the throttle body is the TPS. The TPS reports the throttle position to the PCM and the PCM uses it for fuel, spark advance, shift points, and other purposes.

https://www.youtube.com/watch?v=G83vmQijMg4

The stalling, hesitation, and faltering on acceleration could be due to many causes. Are there any trouble codes, or is the MIL on alerting you of a problem/code?

[rcweston]

Originally Posted by Blue Bowtie

The stalling, hesitation, and faltering on acceleration could be due to many causes. Are there any trouble codes, or is the MIL on alerting you of a problem/code?

I got the engine to fail and stop today. It happened while slowing for a turn while decelerating.
This time it did set a code. P0102. my book and simple reader says it is MAF low signal.
'll try and study up on it tonight.
any sugestions would be helpful
Thanks Rex

[Schurkey]

ASIDE from verifying all tune-up items--air filter, spark plugs, plug wires, throttle-body cleaned of deposits, IAC, PCV and EGR functioning properly with no excess carbon deposits, O2 condition, fuel pressure/filter condition, cranking compression, etc...

...you're going to get Schurkey's Perpetual Advice: You need a REAL scan tool that gives you access to the data stream. Reading codes is the very beginning of ECM diagnosis. Best would be to record the data stream so you can "play back" the data for a second or two before the stall or misfire. Then you can study the commanded fuel rate, the O2 readings, IAC readings, and all the rest of the input/actuator activity leading up to the stall or misfire.

I've seen engines stall on turns because the wire harness was being pulled due to excess engine rock because of a failed motor mount. The wire harness connector would break contact when the engine rolled to the side. Anything is possible. You might verify that the MAF is not faulty.

[Blue Bowtie]

Without connecting a scanner and continuously monitoring the MAF signal, I can tell you that I've had at least three Buick 231s which have had electrical connector problems in the MAF circuit. The connector at the MAF, the harness in the engine compartment, and the MAF sensor itself are suspect.

One possible way to determine this is to disconnect the MAF entirely and run without it. The engine may take a bit more cranking to start but will run on backup fuel parameters. Of course, a trouble code will be set. But if the engine does not stumble or stall any longer, the MAF circuit should be investigated in depth. New MAF sensors are not inexpensive, so diagnosis of the circuit is going to be better than just throwing parts at it indiscriminately.

[rcweston]

Originally Posted by Schurkey

...you're going to get Schurkey's Perpetual Advice: You need a REAL scan tool that gives you access to the data stream.

Thanks Schurkey, I would love to have a real scan tool, but it's not in the picture for the time being. That is one of the reasons I still drive a 98 lumina.
I'm not too bad with electronics and understand when things are explained, that is what makes this forum so valuable to me. But I can see that their is a lot more to the hesitation diagnostic than just replacing a part. I really like to know the real problem. It makes me sleep better at night. A scan tool would really help but I will have to do without for right now. I do have a good dvom ,Fluke 87, and a cheaper Klien and an old analog meter. These are a real help. And I do have access to a scope, well i think I do. It would help on diagnostics in the garage, but as for traveling down the road when it happens. It wouldn't work so well, it's not portable.
For now, I'm hoping that this problem has happened before and someone might be able to focus me in the right direction, even give me their solutions to similar problem. It might just be that my problem is the same or close to the same.
Thanks again for your response. Wish me well.
Rex

[rcweston]

Originally Posted by Blue Bowtie

Without connecting a scanner and continuously monitoring the MAF signal, I can tell you that I've had at least three Buick 231s which have had electrical connector problems in the MAF circuit. The connector at the MAF, the harness in the engine compartment, and the MAF sensor itself are suspect.

One possible way to determine this is to disconnect the MAF entirely and run without it. The engine may take a bit more cranking to start but will run on backup fuel parameters. Of course, a trouble code will be set. But if the engine does not stumble or stall any longer, the MAF circuit should be investigated in depth. New MAF sensors are not inexpensive, so diagnosis of the circuit is going to be better than just throwing parts at it indiscriminately.

Thanks so much for the info. I have learned a lot from this problem as I have tried to study up on it at night. I've earned that the mas, map, iat,and maf sensors all work together and sort of verify each other through the pcm. I've also learned that there is a lot more to learn!!
I will do a lot of checking with the MAF first since that is what is now indicated. I can see how a simple loose wire or connection could be the root cause of this problem. Proving it might be a little harder.
I try the disconnected maf after taking a good look at the connector.
Thanks again and wish me well
Rex

[rcweston]

Originally Posted by Blue Bowtie

One possible way to determine this is to disconnect the MAF entirely and run without it. ... But if the engine does not stumble or stall any longer, the MAF circuit should be investigated in depth. New MAF sensors are not inexpensive, so diagnosis of the circuit is going to be better than just throwing parts at it indiscriminately.

Today I ran the car with the MAF disconnected, It seems that the hesitation and stumbling came to and end. I reconnected it and it stumbled 3 times in less than 2 miles.
I have a meter with a frequency counter. If this is connected to the signal wire out of the MAF, should I see a change in frequency when the hesitation occurs? (car would be idling)
Rex

[Blue Bowtie]

There should be a relatively constant frequency output at a given RPM and throttle opening. If the signal goes to zero Hz (or nearly zero) would indicate an open circuit. The MAF is reasonably easy to remove and inspect, but is not an inexpensive replacement item. Unfortunately, you may be discovering that the hard way. Many of us have been there.

It might also be helpful to monitor the reference voltage at the MAF sensor to determine whether that falls off as well. That could indicate a wiring problem.

[rcweston]

Originally Posted by Blue Bowtie

There should be a relatively constant frequency output at a given RPM and throttle opening. If the signal goes to zero Hz (or nearly zero) would indicate an open circuit. The MAF is reasonably easy to remove and inspect, but is not an inexpensive replacement item. Unfortunately, you may be discovering that the hard way. Many of us have been there.

It might also be helpful to monitor the reference voltage at the MAF sensor to determine whether that falls off as well. That could indicate a wiring problem.

This morning I took some good reading. I found 13.8 v on the (a) + lead, 0.05 on the (b) - lead, and a frequency on the (c) lead. I would have suspected a -5.0 V on the (b)- lead..
After hooking up the frequency counter o the fluke meter, I get about 2.5k hz at idle. It rises as the engine is revved up. But I couldn't get it to hesitate or fail during a 10 min.test.
I then connected a remote wire into the cab and reconnected the frequency meter on the dash in easy sight. After about 8 miles of driving, it hesitated. the frequency dropped from 4.2k hz to 2.0k hz and then right back to 4.2k hz. It hesitated a second time, this time the frequency rose to 7.1k hz the back to normal. A 3rd and 4th time it dropped to 0.138 k then back to normal.
I'll try it again with 2 meters, one one the supply voltage and one on the frequency output.
But I am wondering if the (b) - lead should be ground reference or -5.0 volt reference?
Thanks for the help, any other suggestions would be greatly appreciated.
rex

[rcweston]

Originally Posted by Blue Bowtie

It might also be helpful to monitor the reference voltage at the MAF sensor to determine whether that falls off as well. That could indicate a wiring problem.

Making checks at the MAF connector, it appears that one lead is a supply voltage lead, a second lead is a ground lead (not a -5v supply), and the third lead is for delivering the generated frequency back to the PCM to be used to control the engine. I found the supply lead and the ground lead to be constant and not having periods of sudden changes as I previously found with the frequency lead (even when the frequency goes hay wire).
I am confident now that the MAF is the problem, since I took these reading right at the connector of the MAF.
After checking around, The MAF was quite expensive at the parts store, from $100 to $160. At rock auto they had one for under $60. I tried to get a used one at the salvage yard ($5) other yards up to ($60), but they didn't have the correct one. Might as well buy a new one if your going to pay $60 for a salvaged one! I found one on Ebay for under $20 and thought it would be worth it to give it a try. IT WORKED, but was cracked. They sent me a second one to replace it and the car runs beautiful! Then this week I got a recall from Chevy to replace the manifold leaking oil . It has also been done. This car hasn't been so good in a long time! Too bad the car looks horrible from the pealing GM paint job!!
Thanks everyone for taking a few minuets to share your knowledge and your help.
Rex

[Blue Bowtie]

Good news - And good procedures, too.

I hesitated suggesting simply replacing the MAF without performing diagnosis because the MAF is so expensive. You did your homework and basically eliminated anything else, so replacement was a good call. I know that far too many people have replaced $150 MAF sensors due to a failing connection, and have had to go back later and repair the problem with the $5 connector.

Peeling paint on a Lumina? I'm guessing that it is white, since there were problems getting the white water process paint to stick to the gray primer for several years at GM. The good news is that repainting with real, solvent-based paints (like PPG DBU) will solve the problem so long as all the poorly bonded original paint is scuffed down to primer.

[Tech II]

Do you have a Bluetooth smartphone, tablet, or laptop? How would you like a scan tool for under 20 bucks?

Go to Amazon.com, and look up Bluetooth OBD II interface.....there are many for under $20.....I have an expensive scan tool, but this little baby does practically everything my scan tool does......I downloaded Torque Pro for $5 from the google store to my smartphone, and my smartphone is my scan tool......you can also connect to tablets/pc's for a bigger screen....

Read/clear codes, see live data, even plot/graph data from sensors......these things will put scan tools out of business for the price...

[Blue Bowtie]

...Except for my Venture issue with PK3 faluts.

[rcweston]

Originally Posted by Tech II

Do you have a Bluetooth smartphone, tablet, or laptop? How would you like a scan tool for under 20 bucks?

Go to Amazon.com, and look up Bluetooth OBD II interface.....there are many for under $20.....I have an expensive scan tool, but this little baby does practically everything my scan tool does......I downloaded Torque Pro for $5 from the google store to my smartphone, and my smartphone is my scan tool......you can also connect to tablets/pc's for a bigger screen....

Read/clear codes, see live data, even plot/graph data from sensors......these things will put scan tools out of business for the price...

Tech II, Where were you a couple of weeks ago?? This little device is great!!
It appears that it is a two part system; part one is the app or program on a phone or a pc device and part 2 is the plug in module used to transmit the data to the device in part one.
This looks like something I could really use.
As for the apps, some seem pretty simple such as the code reader I have and others seem to have lots of options such as sensor reading and real time graphing of a lot of components.
You mentioned you use the Torque Pro app, but what do you use for the plug in device?
Thanks for opening up a whole new world of info with a device I had no idea even existed!
Thanks for the info
Rex