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Discussion Starter · #1 · (Edited)
I'm trying to analyze my HPT logs to diagnose a weird-ass problem causing insanely rich AFR at idle once the car has been running for 10-15 minutes. I'm seeing AFR values in the 10-12 range, and vacuum drops from ~25mmHg to ~10. When this happens, the car sounds like a Diesel that's about to explode.

Looking over the logs, I see my MAF staying at or around 0.5lb/min, with occasional spikes when under hard acceleration. On the HPT graph, this is near the floor. The graph follows the MAP *somewhat*, but somewhat inconsistently.

Suggestions? Is there a convenient way to test the MAF or do I need to just eat the cost and get a new one in the hope that it solves the problem? (I hate doing that. As an engineer, I frown heavily upon the shotgun approach to problem solving.)

One test idea: Turn the car on (not started), fire up HPT, remove the MAF from the intake pipe and hit it with my air compressor. I foresee this being entertaining, but perhaps less useful than one might desire. Also, without an idea of what the readings are supposed to be, the resulting data would be difficult to interpret.
 

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Discussion Starter · #3 · (Edited)
What are your stft readings before/after this happens?
This is sitting at a stop light for a few seconds:

JUST before,

LTFT = 15.6
STFT= -14.8%

Just after the problem starts (pretty sharp delta on the graph)

LTFT = 14.8
STFT = -1.6%

Spark hits the floor and spikes a bit while it's doing this, as well.

The fuel trims do a sort of saw tooth pattern until I started moving again.


Funny thing:both O2 sensors (B1S1) sort of flattened out while it was happening... Fun fun fun.

In this image, the white line / sample point is right in the middle of the incident while I was stopped at the light. You can see the FTs saw-toothing and the O2 flattening out. MAF is, in fact, on the graph, it's just on the floor and thus nearly invisible.



**Update**

For comparison, here's a section from earlier in the same log, also stopped at a light (I think) where I didn't have the problem. The FTs and O2 patterns are very different:









Thanks
 

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I know that it probably isn't this simple, but I would clean all the connections on things like your MAF, MAPs and HPFP. I'm not a tuner, but the first thing that comes to mind when I see all the inconsistincies in your graphs is either your MAF is bad or you have a bad HPFP/regulator or a bad O2 sensor (although this does seem to stay stable during even pressure).... I would start by cleaning off the connections and plugs even though you've had then off multiple times. If you are a clean freak and clean your motor consistently, this can cause corrosion on those plugs very quickly as I found out!!
 

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Discussion Starter · #5 ·
It appears one of my new cam actuators is bad. (Probably shouldn't have started two threads.) Score one for buying real Delco parts instead of Dorman crap.
 

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How did you determine that?

If your interested watch this video. It'll clear up a lot of confusion and make you hella smarter! :)

 

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Discussion Starter · #7 ·
How did you determine that?
(See the other thread)

Before all of this started, I had a few DTCs, one of which referred to a cam actuator. I replaced them both, and this whole debacle started shortly thereafter. (I did some other stuff at the same time, and it wasn't obvious to me that this was the issue.)

After running out of ideas, I pulled the new actuators and put the old ones back in. (Really, dug them out of the trash, cleaned them up, and THEN put them back in.)

One of the new actuators was broken.



Awesome videos, BTW - thanks for taking the time. We should start a wiki with an interactive diagnostic flowchart. Could even generate it based on a crazy heuristric analysis of forum contents and service manual troubleshooting procedures.
 

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(See the other thread)

Before all of this started, I had a few DTCs, one of which referred to a cam actuator. I replaced them both, and this whole debacle started shortly thereafter. (I did some other stuff at the same time, and it wasn't obvious to me that this was the issue.)

After running out of ideas, I pulled the new actuators and put the old ones back in. (Really, dug them out of the trash, cleaned them up, and THEN put them back in.)

One of the new actuators was broken.



Awesome videos, BTW - thanks for taking the time. We should start a wiki with an interactive diagnostic flowchart. Could even generate it based on a crazy heuristric analysis of forum contents and service manual troubleshooting procedures.
By broken do you mean the ports were not drilled? If we were to play spot-the-difference, that is one thing I see.
 

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By broken do you mean the ports were not drilled? If we were to play spot-the-difference, that is one thing I see.
Ahem, I think he's referring to the giant piece of screen off to the left, that's unwrapped from the left solenoid :lol:
 

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Discussion Starter · #10 ·
Ahem, I think he's referring to the giant piece of screen off to the left, that's unwrapped from the left solenoid :lol:
Yes, that would be the problem.
 

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Discussion Starter · #12 ·
Yes.

On the up side, I have to give Amazon kudos. I went through the return procedure on the website, and they shipped me a new one at no cost (1 day shipping). I just have to return the broken part within 30 days to avoid being charged.

Awefully convenient!
 

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Yes.

On the up side, I have to give Amazon kudos. I went through the return procedure on the website, and they shipped me a new one at no cost (1 day shipping). I just have to return the broken part within 30 days to avoid being charged.

Awefully convenient!
If you purchase from Amazon the service is great. If you purchase from a vendor through Amazon, they can't help much.
 

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Discussion Starter · #14 ·
Of course, I've now received TWO bad exhaust cam actuators.

The first one broke after about 20 minutes (see picture above). The second isn't visibly damaged, but made the car run horribly. Surging, low AFR, backfiring. Not fun. Once again I put the "old" exhaust solenoid back in and most of the problems immediately disappeared.

It struck me as unlikely that I'd receive two bad solenoids. I've reset the computer (to get FT relearn), checked all connections, to no avail. Now heading over to good ol' Reliable Chevrolet to get a real GM part for a ridiculous $50. Hopefully that one will work!
 

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Of course, I've now received TWO bad exhaust cam actuators.

The first one broke after about 20 minutes (see picture above). The second isn't visibly damaged, but made the car run horribly. Surging, low AFR, backfiring. Not fun. Once again I put the "old" exhaust solenoid back in and most of the problems immediately disappeared.

It struck me as unlikely that I'd receive two bad solenoids. I've reset the computer (to get FT relearn), checked all connections, to no avail. Now heading over to good ol' Reliable Chevrolet to get a real GM part for a ridiculous $50. Hopefully that one will work!
I got cursed after participating in this thread, P0014 exhaust cam position code came up this weekend, I'll for sure get an OEM solenoid and hopefully this fixes it.
 

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Of course, I've now received TWO bad exhaust cam actuators.

The first one broke after about 20 minutes (see picture above). The second isn't visibly damaged, but made the car run horribly. Surging, low AFR, backfiring. Not fun. Once again I put the "old" exhaust solenoid back in and most of the problems immediately disappeared.

It struck me as unlikely that I'd receive two bad solenoids. I've reset the computer (to get FT relearn), checked all connections, to no avail. Now heading over to good ol' Reliable Chevrolet to get a real GM part for a ridiculous $50. Hopefully that one will work!
First off, my buddy and I have a saying, "you get what you pay for". And I have lived by that rule for my entire life. Sometimes I get away with it, sometimes I don't. Next, make sure the part numbers are right and you got the right part....
 

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Discussion Starter · #17 · (Edited)
First off, my buddy and I have a saying, "you get what you pay for". And I have lived by that rule for my entire life. Sometimes I get away with it, sometimes I don't. Next, make sure the part numbers are right and you got the right part....
I tell people that all the time. So much for trying to save money. It took over a week to work out the part debacle for the sake of about $13.00. Totally not worth it.

Part numbers matched on the first one (that broke), didn't check on the second but the (keyed) harness connectors matched. (Which is not a guarantee that it's the correct part, but...)
 
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