Looking at a GXP, codes...

[SkiBonne]

Been hunting around for a GXP, this one is pretty cheap, but I'm sure it has a head gasket issue. I am attaching the code list I pulled, let me know what you think.
http://www.pontiacbonnevilleclub.com/ga ... fullsize=1

[RJolly87]

How cheap is pretty cheap? Are you ready/equipped to pull an engine?

The list of codes is pretty disgusting and covering multiple systems.

I don't like it so far, but I am curious to hear more...

[CMNTMXR57]

P0121 - The PCM detects that the TP sensor voltage is not within the calibrated limit of the estimated value for more than 1 second.

P0136 - The powertrain control module (PCM) detects that the HO2S 2 did not transition below 299 mV or above 721 mV during the passive test.

P0137 - The PCM detects that the HO2S 2 voltage is less than 25 mV for more than 80 seconds.

P0171/174 - The average long term fuel trim value is above 19 percent. All of the above conditions are present for 90 seconds.

P0300 - Self expanatory. Probably caused by the lean issue.

P0455 - The EVAP system is not able to achieve or maintain vacuum during the diagnostic test.

P0442 - The EVAP system can achieve a vacuum, but a vacuum decay is detected during the diagnostic test.

The actual engine speed is 100 RPM more than the desired engine speed.

• The PCM detects the IAC test failed 3 consecutive times per ignition cycle.

• The vehicle must enter the above criteria and leave the criteria for 1 second in order to complete one test.

So arm chair QB'ing here, what it sounds like to me is that you have an HO2S issue or wiring issue in those circuits, causing a lean issue, causing the PCM to compensate the idle (expecting certain parameters which aren't happening), which is outside of the expected parameters of the TPS and IAC and you have an EVAP issue (could be or could not be related). While P0136 is susceptible to potential "water" intrusion causing it to flag, doesn't mean that it's necessarily a head gasket. It could simply be water in the fuel. I really wish people would stop going to the worst case scenario right away. There are other indications of headgasket failure that would need to be seen to corroborate with the issues listed above.

[ddalder]

I really wish people would stop going to the worst case scenario right away. There are other indications of headgasket failure that would need to be seen to corroborate with the issues listed above.

I couldn't agree more. Everybody always wants to blame the head gaskets. By this vintage, as we all know (or should know), this isn't nearly as common a problem as it once was. Unlike the Cadillac cars of the 2004 model year in which some did and some didn't, EVERY Bonneville LD8 had revised head bolt threads which helped.

[CMNTMXR57]

Really. Troubleshooting always has you start small and work out those smaller/cheaper items first as process of elimination before going to that level of a problem.

[SkiBonne]

Honestly, I came to that conclusion after a quick test drive and inspect. It's leaking both oil and coolant, coolant level was low, and it ran pretty horribly obviously. The general condition of the car led me to believe that it has been neglected for a while. It needs tires, brakes, alignment, drivability diag and misc interior/exterior cosmetic issues. Currently he offered it to me for $1k to get it out of his sight, either due to lack of use or problems...

[CMNTMXR57]

For $1k, I'd be seriously looking.

Coolant does leak on these LD8's too. Freeze plugs (where mine was), etc... If it's leaking it from the head area, you see a milkshake in the oil, if you see any telltale white smoke, then different story.

So if lack of maintenance is a common theme here, it could just be that it needs some lovin'

[crash93ssei]

For $1,000 if the money was not an issue it would be in my driveway if I was there.

[havoc1482]

The Northstar in these cars isn't as scary as people think. If you are willing to give the car some love after the 1K price then you should absolutely buy it.

[SkiBonne]

Y'all are a bad influence...

[CMNTMXR57]

This isn't the first time anyone has told me this. If you're looking for someone to talk you out of whatever you're interested in... I'm not that person.

[havoc1482]

Y'all are a bad influence...