Wastegate Fault with Turbomaster

[89SWB]

Now that I've got the truck running good and have bypassed the wastegate solenoid with a homebuilt turbomaster, I'm getting code 78 (wastegate solenoid fault) flashing on occasion. Any way to fool the ECM so a code doesn't flash?

 

[JiFaire]

Do you have gauges? How much boost are you running with your homebuilt TM?

Fooling the ECM is done by adding a potentiometer to the MAP sensor circuit, but I'm not sure we should be telling you how to do that unless you know how much pressure you have... right now, excess boost pressure is being compensated for when your ECM sees that code and pulls back on the fuel.

Don't get me wrong, I'll give you the schematic for it gladly, but I do want to make sure you know not to damage your engine by using it improperly (cranking your TM down too much and popping your head gaskets out)

 

[89SWB]

Don't have gauges, but run GMTD ScanTech regularly to check all readings. My boost has always been low, no higher than 2 psi when heading uphill under throttle. Don't typically haul or tow any big loads. Running stock airbox and exhaust, so figured 2 psi on light duty wasn't a big deal. Should it be higher running empty like this?

 

[mfgguru]

There can be variances between gauges and scanners. If the computer is setting off codes, my thought is you are higher than 2 psi. The scanner bases its psi on different readings than a guage, IIRC.

 

[Goldsburg]

I am not 100% sure, but I think that the ECM can throw a code 78 for a low boost condition as well. I am sure that the ECM is looking for boost in a "X to Y" range under certain conditions and when it doesn't read boost in that range, it only "knows" how to throw the code 78. I say this because both ebay purchased 6.5 trucks that I have bought had non-functioning wastegate systems and would occasionally illuminate the CEL with a code 78 resident in the ECM. After the installation of the Turbomaster set to 8psi (and removal of the vacuum pump), everyone was happy!!!:hurray:

With that being said, couldn't a bad Baro or Map sensor also do the same thing?

Regards,

 

[89SWB]

To the best of my understanding, ScanTech calculated boost pressure as the difference between barometric pressure and pressure inside the intake manifold. Both readings are taken by the MAP sensor, barometric reading taken as soon as the ECM gets power from the key in the "on" position and kept in memory, then the dynamic readings inside the intake manifold upper plenum as the engine is running.

Goldsburg - is your truck running 8psi at idle?

 

[Acesneights1]

I think Goldsburg meant WOT. GMTDScan reads pretty accuratlely. As was said I think you may be experiencing too low a boost. According to Bill Heath , inventor of the turbomaster, they can run upto 14 pSI WOT. I personally am running mine 10-12. At Idle you won't see much of anything and loaded(towing) and unloaded(not towing) will also give different readings. Buy a boost gauge. 35$ is alot cheaper than new headgaskets and it's very easy to install.
2 PSI under load uphill is way too low.

 

[JiFaire]

Golds was correct, your code 78 is "boost out of range" which could be either high or low. (in your case, 2 psi is 'way low). Without a chip or reflash, you cannot run sustained boost over about 11-12 psi without coding. I'd aim for a sustained boost around 8-9 psi. Crank it up a bit and see what happens.

It appears you know not to blow things up, so here's the diagram for the boost-fooler circuit. I doubt that your GMTDscan will work right after you install this, because it 'fools' the sensor that GMTDscan uses to read manifold absolute pressure.

So, you'll need to buy and install a boost gauge.

Have fun!

 

[Slim Shady]

Golds was correct, your code 78 is "boost out of range" which could be either high or low. (in your case, 2 psi is 'way low). Without a chip or reflash, you cannot run sustained boost over about 11-12 psi without coding. I'd aim for a sustained boost around 8-9 psi. Crank it up a bit and see what happens.

It appears you know not to blow things up, so here's the diagram for the boost-fooler circuit. I doubt that your GMTDscan will work right after you install this, because it 'fools' the sensor that GMTDscan uses to read manifold absolute pressure.

So, you'll need to buy and install a boost gauge.

Have fun!

You could also just run a forward biased zeiner diode of 3.5 volts and then a 1000 ohm resistor to the ground circuit. It will clip maximum signal voltage when the diode hits 3.5 volts. The zeiner diode will open and keep sig return line voltage at 3.5 volts until the forward bias voltage drops below the zeiner diode forward bias voltage. Then revert back to normal operation. :crazy:

 

[JiFaire]

Slim, there's a reason I let you and BA build turbos in your garage...

... it's because i don't understand a word you say. That last explanation went whizzing overhead at about mach II. I need small words

Zeiner Diode? Is that the same as a Feldercarb gasket?

89, do what Slim says.:rofl: I would.

 

[RadioMan]

Feldercarb gasket??? Not on a diesel... Well maybe a hybrid diesel?

Google is your friend - Try "zener diode". A simple device - Just 2 wires. Getting fairly expensive though - some go for as much as 32 cents! Used to be a dime, or less, each!!

[$.32 is from Mouser Electronics - May be even more at Radio Shack]

 

[JiFaire]

So, if I'm reading this circuit right, using a zener diode in this fashion will put a 3.5v 'MAX' value on return to the PCM (the lt green wire)? Below 3.5v, everything will operate normally?

GMTDscan then would read boost just fine up to a maximum value and then just stay there until the boost came back into range? Cool... kind of like a peg in an old speedometer... when you're on the peg, you know you're going faster than that, but you don't know how much?

 

[RadioMan]

Cool... kind of like a peg in an old speedometer... when you're on the peg, you know you're going faster than that, but you don't know how much?

But in this case you, not the PCM, will know how much boost you're running because of the gauge you've installed.
You do have a boost gauge - Right? (Not seeing one in your sig) Otherwise you're taking a real chance of blowing the motor with these mods! (Well...At least the head gaskets).

 

[JiFaire]

Didn't list gauges... they're like mandatory equipment!

Thanks guys, for the explanations on the Zener diodes... I like it! (Something about an old bear learning new tricks)