fixed resistor to fool boost

[norm]

Ok, now, I am going to install boost gauge and turbo-master that I currently have on the work bench.

I do not plan on running crazy-boost, but with concern about setting codes at slightly above threshold, am considering installing a resistor in MAP green wire (instead of pot).

Any disadvantage to putting a 10K ohm resistor in, or should I get a 5K?? If boost is fooled "too much", will it code for low boost?

Any advice or experience would be greatly appreciated!

[rjschoolcraft]

I've never seen a code for low boost...

[norm]

The only times I have seen the low boost code is when the WG solenoid has given me trouble and when a vac line cracked and could not pull the WG actuator into action.(DTC 62)
(with stock setup)

[rjschoolcraft]

I've had complete loss of boost several times in the past due to various failures. Never once set a code.

[Kennedy]

Ron,

That's a function of my high perf chip. Rather than having the PCM get crabby and dump vacuum, it's been neutered altogether. We did this because we know that low boost is worse than high boost and the wastegates just don't stick in high boost mode...

[rjschoolcraft]

That's interesting...

One of the failures I refer to was prior to installing your chip. Running with the stock chip, coming up from Pensacola, FL in April 2003, the Wastegate Solenoid failed. My boost gage read zero, black smoke rolled, power was non-existent... no code at all. I limped to a Chevy dealer in Montgomery, AL, bought a solenoid, installed it and was on my way.

[JohnC]

Originally posted by ronniejoe:
My boost gage read zero, black smoke rolled, power was non-existent... no code at all.Agreed. When my vacuum pump failed there were no codes set either. DTC 62 refers to the circuit voltage being "low" as in less than the minimum reading for the sensor, not the manifold pressure being low.

[HANK1948]

I have a 236 code I cant get rid of ,I have a turbo master and a adjustable pot on the boost sensor(green wire) Ive replaced the boost sensor and wastegate solenoid still get the code. Ive turned down the boost controler to stock setting 8lbs. Still get the code, I have a snap-on scanner and I notice when it sets the code the fuel output drops to 50mm from 65mm , do I need a electronic boost fooler?

[norm]

1. Seems like maybe my code 62 (along with 31, and 19 occasionally) is a different problem. Anyone know why 31 and 62 would come up? Can't say it's running poorly, just uses too much gas and oil, but...

2. On original question, I suppose the resistor (10K ohms, 1/2 watt) will hold off a code if the turbo-master is adjusted just a bit up, do you think? (yes, gauges). (Can not afford chip at this time)

[Turbine Doc]

RJ,
In OBDII codes you don't get a hi or lo boost you get a boost out of range, I had one fail Hi, when shifting to Heath reflash between 3rd & 4th shift, boost would clip to 0 then back to 15 after the shift and I would get intermittent SES lite P0236 IIRC, anyway checking with scanner was seeing what converted to 42 psi boost, a tad bit high for a GM-8's output. swapped to a new MAP sensor and it was fixed.

Hank since you are running a TM you most probably will need a fooler or a fixed resistor, since PCM wants to clip boost to match it's GM programed curves for boost vs rpm/load, with TM it can't control the WG actuator any more; so only thing it can do is defuel to correct, IIRC TM no chip reflash is supposed to peak 7 psi cruise 5 maybe you can lower some more and clear code, also could be defueling on high IAT, what does your scanner show for IAT when this is happening.

As JK indicated above rechip fixes the curve so you don't have to "fool" the PCM into not knowing you are running with higher boost levels I'm pretty sure your 96 is an OBDII which requires a reflash PCM, I'm running Bill Heath's reflash and highly recommend it,I think I saw where Matt-Max is running a Westers reflash he reports good result as well.

[ 11-02-2004, 06:44 AM: Message edited by: tbogemirep ]

[Spindrift]

Why would Hank need an adjustable pot on the boost sensor? Without the additional fuel that a reprogrammed ECM would provide, any boost above 7 psi isn't providing much, if any, additional power. Remove the pot. Right...wrong?

[rjschoolcraft]

Increased boost can increase power even without increasing fuel...

Especially on the 6.5. Increased boost seems to increase the overall volumetric efficiency of the engine. You can make more power for the same heat input.

[gmctd]

Factory fuel curves allow 20psi Boost easy - was limited to 7-8psi with no charge-air cooling, coolant upgrades and factory exhaust.

'nother words - restrictions to prevent overheating.

Enforcement of those restrictions are -

High Boost @ ~15psi - after ~20 seconds, PCM will reduce WG Duty Cycle to reduce Boost.
If WG is stuck, or otherwise prevented from opening, PCM will reduce fuel rate, going into 'limp home' mode, resettable with power-down cycle.

High Intake Air Temps @ 237deg - PCM will reduce WG Duty Cycle to reduce Boost.
If WG is stuck, or otherwise prevented from opening, PCM will reduce fuel, go into 'limp home' mode, resettable with power-down cycle.

Same for high Engine Coolant Temps.

Adding a resistor to MAP output offsets Boost value the PCM 'sees', allowing more actual Boost without setting the DTC.

If you have 15psi Boost, but PCM 'sees' only 10psi, PCM is happy, engine is happy, you're happy - until you look at the EGT gage (which you should already have installed by now), and Engine Coolant Temp gage, which high reading is indicative that you should have already installed the engine coolant upgrades, and the exhaust upgrades, and the PCM goes into 'limp home' mode beacuse IAT's went outta sight without the required charge-air cooling.

All part of a required package - don't leave home without it, if you plan on running over ~10psi Boost.

[Spindrift]

There's always an education just waitin' to happen. Half the time you don't even have to ask. Gotta' love it.

[HANK1948]

My EGT's have never been higher than 1000 deg. (post) my IAT have been as high as 225 deg. but it seems to set the the code at any time ,it seems to set it less when towing, it strange my boost isnt any higher the factory (8lbs) so why the code?

[gmctd]

Is the TurboMaster controlling the Wastegate, or the PCM\vacuum system?

The pot on the MAP offsets the Boost values the PCM reads, so the scanner reads and displays those offset values as well.

In your OBD-II, PCM reads Baro on the MAP during the Wait To Start interval, so the offset also effects the baseline reference the PCM uses for controlling Boost, and setting the DTC.

Map output is ~2.4v at Atmospheric pressure - adjust the pot for ~14.7psia at idle, kill the engine, restart, go for a spin to see what actual pressure the TM is adjusted for.

This will give you a base reference to work from.

Also check vacuum for ~25"hg at the pump, ~15"hg at the WG Servo at idle if still using that system.

[HANK1948]

GMCTD, thanks for your help. To answer your question, yes the turbo master is running the wastegate, when watching the scanner I have noticed that the boost value is around 100-140 kpa. I dont know what this means but the value doesnt move while driving. the baro usally is the same as the boost value. When you say adjust the pot for 14.7 I not sure what you mean?

[gmctd]

kPa is Euro Units of Measurement for pressure - can be converted using Metric-English charts.

Not familiar with Snap-On Mt2500 scanner, but seems as tho the Units of Measurement should be selectable from a menu - DP member tbogemirep has more info on that.

The value you're seeing should change with the Boost sensor (MAP) output, representing varying Boost levels - PCM uses that input for Boost control.

To get a baseline reference, the pot must be adjusted for full output from the MAP - no offset - where 14.7psia is 14.7psia.

Then, you can see if DTC-236 is set under normal condition with the TurboMaster adjusted to the current setting.

[Turbine Doc]

Using MT2500 even if English units are selected for some reason boost is still displayed as kPa kilo Pascals (metric) when logging data I write down metric unit then convert using an web based conversion program http://www.onlineconversion.com/

[gmctd]

101.33 kPa is 14.7psia