AutoTap Users - Ever encounter DTC# P0234 - Boost Limit Exceeded?

[TopRacer]

I dont have the autotap in the car all the time because i need to buy a bracket for it, so on my way to Atco last saturday for autox i brought it for some comparison on my runs...

I plug it in before i go and notice that i have DTC# P0234 - Boost Limit Exceeded in the history...

I only have K&N 9" filter and cat back and sometimes might see the boost gauge hit just before the line on the stock gauge... i used to see it hide the line without the catback...

Does this mean that the PCM can tell if we have exceeded the factory set boost? If so, this would suck for those demodding and needing to go to the dealership and not knowing that this DTC can be stored in the PCM.

I had this once before about 3 months ago and didnt post because i lost the number and cleared the DTC...


I have tried using "Intake Manifold Absolute Pressure" to read boost, but no luck... anyone else have an idea on how to read boost with AutoTap?


Can anyone else with an autotap confirm that they have had this before?

 

[DD2000GT]

Never seen that one before. When I had just a densecharger and stock exhaust, my boost gauge pegged BEHIND 10, when I opened up the exhaust it dropped back to around 8.5 or 9. I never got that code... What run Cobra do you have? Maybe it is something Ford built into the later runs because of the pervasiveness of people putting smaller pulleys on... :shrug: My car was built Sept 13, 02.

 

[TopRacer]

I have one of the first runs... Built in June of 02 so whatever that computer code is that is what i have...

I dunno... its odd becuase i tried to make it happen for the passed couple of days and it wouldnt happen again...

 

[NorCalRedfire]

Intake Manifold Absolute Pressure and subtract 14.7 gives you the boost. Don't know anything about the error message. I run the Palm autotap all the time and I've never seen that message.

 

[TopRacer]

thanks...

 

[Smrgol]

That DTC is potentially more than a simple "high boost" condition. The following is from the Ford Powertrain Control/Emissions Diagnostic manual for 2003:

P0234 - Supercharger Overboost Condition

Description

The PCM disables (bypasses) the supercharger boost and sets a diagnostic trouble code (DTC) to keep from damaging the powertrain (engine or transmission) during potential harmful operating conditions.

Possible Causes

-Brake torque (brake on and throttle at wide open)

-Transmission oil temperature (TOT) exceeds calibrated threshold

-Engine over temperature

-Ignition misfire exceeds calibrated threshold

-Knock sensor (KS) failure or knock detected

-Low speed fuel pump relay not switching

Diagnostic Aids

Check for other diagnostic trouble codes accompanying the P0234 or check appropriate and available PIDs related to above possible causes.

 

[Dana]

I think you can knock out a couple of the possible causes:
No knock sensor on this motor.
No trans temp sensor.
Brake torque - tough to do on manual trans, but not impossible I guess...

Did you try the boost reading again yet?

Dana

 

[DD2000GT]

Monitor misfires with the autotap and see if this could possibly be your problem. Just get it out on the highway and do a few high RPM pulls (use a lower gear than usual). Have you replaced your spark plugs from the factory set?

 

[TopRacer]

Originally posted by dwtalso

Diagnostic Aids
Check for other diagnostic trouble codes accompanying the P0234 or check appropriate and available PIDs related to above possible causes.

Thanks... There were no other DTC's with the P0234. It was in history. Could the boost dump valve trigger this?

Originally posted by Dana
Did you try the boost reading again yet?

Do you mean with the Abs. Intake Man. Press.? If so, yes and it works well... I used -14.5 as that is what shows on the AutoTap with the ignition on and engine off... I hit a max of 8.3psi...

Originally posted by DD2000GT
Monitor misfires with the autotap and see if this could possibly be your problem. Just get it out on the highway and do a few high RPM pulls (use a lower gear than usual).
Have you replaced your spark plugs from the factory set?

Which are the best parameters to read to determain misfire?
No, I have not replaced the factory spark plugs... 16k miles...


Thanks for the help and keep it coming... you guys got me a little worried...

 

[Smrgol]

Originally posted by TopRacer
Thanks... There were no other DTC's with the P0234. It was in history. Could the boost dump valve trigger this?

Reading the description it sounds like the PCM opens the boost bypass valve as a result of whatever caused P0234. In other words, something happened to cause the PCM to store P0234, at the same time the PCM opened the bypass to "save" the drivetrain.

I would suspect that a transient wouldn't cause P0234, like hitting the rev limiter, especially since I do that all the time and I've never seen this code. I would also not believe that boost pressure as measured at the manifold is the issue since folks have pumped as much as 30 psi through the system and they didn't mention this code being thrown.

As well as monitoring misfires I would also get a fuel pressure gauge on there and take a look at it. Maybe meter the fuel pump as well and make sure it's healthy. I don't even know if this car has a low speed fuel pump relay but maybe that's a hint. Also, a couple of folks had issues with a fuel pressure sensor. Might be worth checking on too.

And a *real* reach here but could a brake be dragging on you? That might fool the PCM into thinking that there's a high brake torque condition.