This would be a good scenario to be able to watch live data when the idle starts slowing down and it dies. Pretty much all the bidirectional scanners out through these days have that ability. (As well as reading trouble codes and clearing them of course) Cheaper in the long run than to keep throwing parts at it. You can select several parameters for it to display and track.... Drive around with it plugged into the OBD2 port..... Either look at it when the symptoms show up or replay the live data afterwards. It should point you exactly to the component that's causing the issue.
2007 Yukon Denali Intermittent Crank No Start
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Maxpower_454
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Whats the most common scanner that has that capability? Where do I start?
Just look on Amazon for bidirectional scanners, and read the description to make sure it has live data capability. Autel make some pretty popular ones. Generally, the more you pay the more features it has. Doing a crankshaft or Cam relearn is a good one, as well as the ABS bleeding and being able to send commands to different modules to test them. There are some inexpensive ones on the market now that do all that and more. It pays the shop around and look at the features and make sure you read the reviews. It's hard to beat a Tech 2, the actual tool GM uses for diagnostics... but finding a genuine one tends to be rather expensive. There are Chinese clones out there that seem to work fairly well. Any of the above are really a necessity these days. They usually pay for themselves the first one or two times you use it.... When you look at what the dealer or shops charge for a simple diagnostic.
in general, if you don't need to use it across different platforms. the clone tech 2 is the cheapest easiest to use.
I don't believe I've seen anyone show how to graph out can bus stuff with them. but for 200$ it's pretty hard to beat. I keep mine in the truck during any road trip.
I don't believe I've seen anyone show how to graph out can bus stuff with them. but for 200$ it's pretty hard to beat. I keep mine in the truck during any road trip.
Jarhead123
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I had the same issue. Drove me nuts for weeks. Turns out it was a bad ground cable running to the alternator. I replaced it a few years ago and never had a problem since. Doesn't make any sense to me but it worked.
Bad ground connections on these vehicles create all sorts of havoc. I suspect it has to do with the electricity searching through other modules looking for the ground. Sets off all sorts of warnings.... And many times it's just the battery terminals, ground cable, the strap to the firewall...
Charlie207
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Don't forget the ground connection down below/behind the PS pump & bracket, on the block. The cam position sensor is grounded there, and that's a prime spot for rust and corrosion.
Maxpower_454
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Thanks - I'll check that one
Maxpower_454
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So yours would stall and then not start after coming to a stop?
Maxpower_454
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UPDATE!!!! - I had some time to troubleshoot this today. I was actually able to replicate the stalling and I made it stall right at my house so it worked out great.
I had my HP Tuners logging when it stalled, when I unsuccessfully tried cranking, and then when I tried cranking successfully.
I tried starting fluid - no change
I tried disconnecting the battery - no change
I tried disconnecting the MAF - no change
I finally tried holding my foot to the floor on the gas pedal and it fired up. It acted like it was flooded.
I logged:
TPS compared to absolute TPS - track and look good
******MAF frequency - Seems to be higher than normal right before it stalled
See attached Pictures of my log. Higher MAF freq correlates to more fuel output. Inj duty cycle was a flat 1.5% when idling good but when idling rough right before stalling it was bouncing around and even went up to 3.0% so double the fuel it was using to idle before.
I have a new MAF. Could this be my issue? Anything else I should look at before replacing the MAF?
I had my HP Tuners logging when it stalled, when I unsuccessfully tried cranking, and then when I tried cranking successfully.
I tried starting fluid - no change
I tried disconnecting the battery - no change
I tried disconnecting the MAF - no change
I finally tried holding my foot to the floor on the gas pedal and it fired up. It acted like it was flooded.
I logged:
TPS compared to absolute TPS - track and look good
******MAF frequency - Seems to be higher than normal right before it stalled
See attached Pictures of my log. Higher MAF freq correlates to more fuel output. Inj duty cycle was a flat 1.5% when idling good but when idling rough right before stalling it was bouncing around and even went up to 3.0% so double the fuel it was using to idle before.
I have a new MAF. Could this be my issue? Anything else I should look at before replacing the MAF?
Attachments
You should look for the MAF reading in g/sec at hot idle. It should be very close to the engine displacement in liters.
You may also want to look at the intake air temp (IAT) and the engine coolant temp (ECT) to see if the readings make sense. Either one of those being incorrect can cause over-fuelling.
You could also have a leaky injector or a purge valve that's stuck open (or intermittent) causing excess fuel.
You may also want to look at the intake air temp (IAT) and the engine coolant temp (ECT) to see if the readings make sense. Either one of those being incorrect can cause over-fuelling.
You could also have a leaky injector or a purge valve that's stuck open (or intermittent) causing excess fuel.
Although it's normal to not notice any issues after changing either the cam or crank sensor - or both -- sometimes the relationship between the two can get skewed. The CASE relearn is quick and easy and will rule out any issue with the cam-crank correlation. That's why it's a suggested procedure.
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Maxpower_454
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ECT and IAT are both on the attachments I posted... They're good.
The MAF reading on the graph is a frequency. Can you correlate that MAF frequency into g/sec (that's grams per second) which is an easily understood and relatable value?
Maxpower_454
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Higher the frequency, higher the mass flow. Really no need to convert. It will just be a calculated value anyway.
new maf you say? what brand.
so the point of looking at the maf in g/sec is because you can tell if it's actually reading the correct amount of air flow. at warm idle it will read about what the engine size is. kinda wild, but it works. it's a good way to check if the maf is reading correctly.
it's not as simple as just reading a freq for airflow. these gen 4 ecm's do everything ofd airmass. timing and everything is off the maf signal blended with other stuff. I have a log before and after cleaning the maf and it's running in a different part of the timing map based off the airmass reading change just from some maf cleaner in a q tip.
but yes, 3ms injector as idle sounds high and having to use clear flood mode to get it to start is classic flooded with fuel..
did you check the alcohol %? I don't remember.
so the point of looking at the maf in g/sec is because you can tell if it's actually reading the correct amount of air flow. at warm idle it will read about what the engine size is. kinda wild, but it works. it's a good way to check if the maf is reading correctly.
it's not as simple as just reading a freq for airflow. these gen 4 ecm's do everything ofd airmass. timing and everything is off the maf signal blended with other stuff. I have a log before and after cleaning the maf and it's running in a different part of the timing map based off the airmass reading change just from some maf cleaner in a q tip.
but yes, 3ms injector as idle sounds high and having to use clear flood mode to get it to start is classic flooded with fuel..
did you check the alcohol %? I don't remember.
Maxpower_454
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I ended up biting the bullet on a new Acdelco TB and a Delphi MAF. Starts easier and idles smother. I tried to get it to shut off like I did last time but idle held steady like it's supposed to. inj duty cycle is 1.4 to 1.5, TPS % is lower, STFT are near zero and responding normally.
I will report back if the symptoms return but the TB and MAF seem to have resolved the issues I was having.
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