Turbo Wastegate Solenoid Fault Code.

[JeepRocks86]

DTC 78 -Turbo Wastegate Solenoid Fault

It happened under hard acceleration. Is this something I should be worried about? I haven't installed my gauges yet. Is this something I should be worried about?

[More Power]

Probably either a vacuum problem or a wastegate solenoid problem. There's been quite a bit of discussion here about checking vacuum and for how to replace the solenoid... (easy).

Jim

[Artworks]

Check all vacumn lines, especially the connectors, wiggle them and look for cracked and broke tips. Selonoid is about $35 cnd. I had both cracked lines and broken connectors as well as bad solnoid .

[Robyn]

The 78 code is a common fault that can happen with these systems.

The solenoid (Located near the rear of the LH Valve cover has an electrical connection plugged into one side and the vacuum lines plugged into the other.

The solenoid can fail electrically and casue the code to set or a leaky vacuum line or faulty vacuum pump can result in alow boost condition
that can also cause the code to set.

Check vacuum at the pump (Front RH side of the engine blow the AC Pump) you should see a steady 26" HG with engine at idle.

If the needle on the gauge is wobbling all over or reading low then the pump is junk.


Vacuum OK then pump is fine

Check lines runing from the pump to the solenoid (should have 26" HG at the solenoid)

Line to solenoid OK

Check line running to waste gate actuator

Gauge reading should be around 20" or so if very low with engine running then line may be cracked or solenoid is bad.

If the lines check out ok and there is vacuum present to the solenoid but not beyond, then the solenoid is the culprit.

If there is vacuum present at the waste gate actuator but the rod on the turbo can be moved freely then the actuator is likely bad.

The code 78 can be tripped in a couple ways. The solenoid can fail internally and the resultant electrical fault can cause the issue or, low boost under power (heavy throttle) can cause the ECM to complain.

The OBD 1 systems are not very specific as to what the exact cause of the issue is but will get you in the ball park.


Low boost due to a waste gate system failure is the root cause.

Electrical failure in the solenoid
Vacuum line failure between the pump and the solenoid
Vacuum line failure between the solenoid and the actuator
Waste gate actuator failure
Vacuum pump failure
Electrical connection failure at the solenoid or ????


Under high power demand the ECM does not see the level of manifold pressure it expects to see so the fault code sets.

To sort this out should not take more than a few minutes.
The Solenoid is a MA General item.

Many of us have scrapped the vacuum system and installed the Turbo master system from Heath Diesel.

This is a spring device that replaces the vacuum actuator and controls boost manually with an adjustable spring.

This system works best when used with a power chip from Heath too.

The exhaust system needs to be free flowing (larger than stock) to gain the most from the turbo master and the chip.

You can set a turbo master to allow the boost to go to about 5-7 PSI max and do fine with it.

Anything over 8 PSI will likely trip an overboost code and cause the thing to defuel. :confused:

If it defuels it will run in limp mode until to shut it off and restart.


The vacuum system is another case of "The more they overthink the plumbing, the easier it is to plug up the drain" :eek:

It works fine while it lasts. :rolleyes:

NOW all this said, yessssss you need to worry a little bit, but instead FIX IT
Low boost causes High exhaust gas temperatures and is not good for things.


Keep us posted


Missy