Vac/Boost Gauge questions

[iRealty24]

My 95' C3500 smokes really bad when I mash the gas or under load. I towed about 5000lbs with it and it really struggled on upgrades and black smoke poured out under the load. I think it may have been defueling. I do get the DTC 78 - Turbo Wastegate Solenoid Fault and SES light at 55-60MPH but I tried running with a "temporary" manual wastegate closing device and the boost did not increase on my gauges. I'm getting about 3PSI boost at full throttle - 3500 RPM - 75+MPH.

As I am trouble shooting my turbo//air fuel issues, I am wondering if the placement of my gauge sending unit is adequate for my Boost/Vac gauge? I'm not sure which sensor I relocated (please feel free to tell me)? but I used that port on the intake manifold and installed a T in lieu of drilling a hole in the intake manifold. I was trying to avoid doing that If I could? I have uploaded the pictures of everything and want to know if the location of my gauge line is the problem or if I really have barely 1" of Vac and 3PSI of boost? I hooked a vac pump to the end of my connection and was able to get 28" of vac on the gauge so I think the gauge and the lines are good.

I have not checked the crossover pipe just yet because I wanted to see if the gauge location was adequate prior to continuing the troubleshooting process.

Any help/advice is greatly appreciated,

Ellwood

95' GMC C3500 6.5L Dually 5" Stack Exhaust 4" Aero Exh Turbine 185k miles

[grancito]

My 95' C3500 smokes really bad when I mash the gas or under load. I towed about 5000lbs with it and it really struggled on upgrades and black smoke poured out under the load. I think it may have been defueling. I do get the DTC 78 - Turbo Wastegate Solenoid Fault and SES light at 55-60MPH but I tried running with a "temporary" manual wastegate closing device and the boost did not increase on my gauges. I'm getting about 3PSI boost at full throttle - 3500 RPM - 75+MPH.

As I am trouble shooting my turbo//air fuel issues, I am wondering if the placement of my gauge sending unit is adequate for my Boost/Vac gauge? I'm not sure which sensor I relocated (please feel free to tell me)? but I used that port on the intake manifold and installed a T in lieu of drilling a hole in the intake manifold. I was trying to avoid doing that If I could? I have uploaded the pictures of everything and want to know if the location of my gauge line is the problem or if I really have barely 1" of Vac and 3PSI of boost? I hooked a vac pump to the end of my connection and was able to get 28" of vac on the gauge so I think the gauge and the lines are good.

I have not checked the crossover pipe just yet because I wanted to see if the gauge location was adequate prior to continuing the troubleshooting process.

Any help/advice is greatly appreciated,

Ellwood

95' GMC C3500 6.5L Dually 5" Stack Exhaust 4" Aero Exh Turbine 185k miles

You have tee-d the intake temp sensor, the boost gauge will work fine but not the temp sensor, not a real problem. Vacuum pump tests for leaks, but test the vacuum at the waste gate while the engine is running, needs to be 15".

[grancito]

Can't add to the last post. "Temporary waste gate control" has to be a very strong spring. Are you getting fluctuating boost pressure above 2500 rpm and a drop in pressure?

[iRealty24]

Thanks for you reply...How/where do you specifically test vacuum at the wastegate?

The answer to your question is yes, the slight boost pressure that I am getting does fluctuate and goes back to zero after the gears shift and the RPM's drop back down. The boost pressure seems to be zero unless I'm really mashing the gas.

Also, I will try one of the manual wastegate configurations that I have seen on the site and see if any of those work for me.

Thanks,

[grancito]

Pull the tube off the waste gate canister, and connect it to a vacuum gauge. Check the vacuum at idle. Then check the vacuum on the other side of the waste gate solenoid, it should be 20" there, and 15 at the waste gate.

[iRealty24]

I know that the solenoid is bad but I was going to install a mechanical wastegate to eliminate the need for the vacuum pump and the solenoid. My understanding is that the vacuum pump is only used to actuate the wastegate?

[grancito]

Yes, better to have a mechanical waste gate control, it does drop the MPG a bit, but less problems.

[JD_countryboy]

I agree with a grant on the mechanical wastegate being better (more dependable, less parts) However In my own personal testing i have found no evidence of lower mpgs due to mechanical wastegate control, but i havent pushed them to extreme high boost either. I have also found you need a strong spring, but not super super stiff spring. deerfanatic posted good pics with instuctions. if you dont have a welder though, just use a piece of 5/16 allthreadwith a 90* bend on the end to hook to wastegate lever.

[iRealty24]

Thanks guys! I installed a mechanical wastegate control and the boost is now maxing out around 10PSI (that's definitely more like it :)

I haven't towed yet but I'm optimistic that will be better and the black smoke only lasts a short time now ( right at, and shortly after, take off)

Just to clarify, the manual wastegate closes the turbo bypass piping that dumps air into the exhaust and pushes that air into the intake manifold, right?

I assume that's why my engine temperature has slightly increased as well?

Thanks again,

[grancito]

Thanks guys! I installed a mechanical wastegate control and the boost is now maxing out around 10PSI (that's definitely more like it :)

I haven't towed yet but I'm optimistic that will be better and the black smoke only lasts a short time now ( right at, and shortly after, take off)

Just to clarify, the manual wastegate closes the turbo bypass piping that dumps air into the exhaust and pushes that air into the intake manifold, right?

I assume that's why my engine temperature has slightly increased as well?

Thanks again,

A puff of black smoke is normal when you boot it. The waste gate when closed, passes all of the exhaust gas through the turbo, when it opens, the gas goes directly to the exhaust pipe. The increase in temperature is a result of the engine producing more power.

[iRealty24]

I hate to be redundant but i want to ensure i understand what you are saying. Are you saying that the flow is exhaust gasses turning the exhaust turbine when the wastegate is closed (like I have it now) and simply bypassing the turbo all together and going straight out of the exhaust piping when its open (thus "wasting" the exhaust gasses instead of using them to turn the exhaust turbine)?

By the way, I do understand that the exhaust turbine is keyed to the intake side of the turbo which forces air into the intake. I just want to ensure that I am understanding the wastegate function properly as it pertains to this engine.

Thanks,

Ellwood

[trukdoc]

...is a flapper valve in the exh. side of turbo, ALL exhaust spins the turbo and goes out the tail pipe. the impeller{intake side} is on the other end of shaft from turbine{exh. side} impeller pulls in air from filter and pushes it into intake in a volume to match the fuel delivery for power with no smoke...the black smoke you see is caused by "lag" while exh. is spinning turbo up to speed..."lag" time is caused by restrications in the intake and exh. systems..less restriction = les "lag"...ok wastegate is held shut by controller to a preset boost pressure on 94-up with a solinoid controled by ecm.when ecm senses max. boost it trips solinoid and opens to "dump"exh. pressure and there-by slowing turbo and dropping boost by governed engine speed...jd

[grancito]

I hate to be redundant but i want to ensure i understand what you are saying. Are you saying that the flow is exhaust gasses turning the exhaust turbine when the wastegate is closed (like I have it now) and simply bypassing the turbo all together and going straight out of the exhaust piping when its open (thus "wasting" the exhaust gasses instead of using them to turn the exhaust turbine)?

By the way, I do understand that the exhaust turbine is keyed to the intake side of the turbo which forces air into the intake. I just want to ensure that I am understanding the wastegate function properly as it pertains to this engine.

Thanks,

Ellwood

Yes you've got the right idea.

[iRealty24]

Sorry for the long delay in getting back to the thread.

Now that I installed my manual wastegate device, I (thankfully--I thought the turbo was gone) might have too much boost.

Everything was fine until I started towing. There was much more power and much less smoke this time around :). However, when I get to 10 psi boost, going up a hill, and I keep the pedal to the metal :). I think it defuels (not sure but suspected because it felt like something broke and there was a noticeable power drop---maybe it was me because I definitely took my foot off of the gas). Either way, the SES light comes on and stays on when that happens. I checked and it's the exact same code DTC 78 - Turbo Wastegate Solenoid Fault.

I'm thinking this is an overboost issue that I can correct by loosening my manual wastegate device??

Thanks,

[grancito]

Yes it de-fueled from over boost, although it should have got to 13 psi before that happened. You could have a worn valve train pulse, giving the sensor a false reading. I cut a circle of rubber, and stuffed it the hole for the sensor and put the sensor back in. With the sensor blocked, the SES light flashes on for a few seconds once a month, 78 code, as it sees no boost.

[flattire]

hey can u tell me how high the boost should be thanks 4 info.

[grancito]

hey can u tell me how high the boost should be thanks 4 info.

About 11 psi unless the boost sensor hole is blocked off, or a "boost fooler" is fitted.

[iRealty24]

Yes it de-fueled from over boost, although it should have got to 13 psi before that happened. You could have a worn valve train pulse, giving the sensor a false reading. I cut a circle of rubber, and stuffed it the hole for the sensor and put the sensor back in. With the sensor blocked, the SES light flashes on for a few seconds once a month, 78 code, as it sees no boost.

Can you tell me where that sensor is so that I can give that a Shot?

Thanks,

[grancito]

It's a black box, mounted on the intake extension, has two bolts holding it down, the hole is under it. I put a round piece of rubber in the hole and put the sensor back. Wires need to be connected to prevent a sensor code.