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Vacuum solenoid woes (boost control)

T

thedrip

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Location
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I have a bad feeling the answer is get a new solenoid. It doesnt work when installed on the truck. No switching of vacuum at all. Good vacuum pump, no vacuum to the waste gate actuator at idle. I replaced all the cracked plastic hoses, and all the normal troubleshooting steps, to discover the solenoid itself wasn't working. I've had it bypassed for a couple months, but I'd like to get the system working again, so I decided to do a little trouble shooting on the bench. Heres the behavior:

18in vacuum source, solenoid works perfect.
20in vacuum source, solenoid does not work at all.

Since my vacuum pump is quite healthy and makes well over 20in of vacuum, this is the problem. I guess this means the solenoid isn't strong enough to overcome the vacuum, and I need a new solenoid.

I'm doing all this because my truck misbehaves on the interstate. Around town, having the wastegate actuator run straight to the vacuum pump is great. Nice and responsive at low throttle positions, maxes out at 11psi at full throttle up a hill. However, it runs 7-8psi at 65mph down the freeway. Not ideal, and sets code 78 every few minutes.

Unless someone informs me theres some way of supercharging the boost solenoid, I'll order a new one up, and then my truck will work just fine.
 
Sometimes grime gets in and covers the check ball,try spraying some wd40 in each port of the solenoid and give it another chance once it gets rinsed off some.

It may take a couple of try's,cheaper to do that than replace but it may come down to replacement as the best option?

My new solenoid is acting up and I intend to give it a squirt tomorrow.
 
I decided to try my hand at taking apart the solenoid. Its bad, so what did I have to lose? You pry back the 4 metal tables from the mounting bracket, and pull the bracket off. theres a 1/4" steel nub protruding from the back side. give it a yank, and all the internals come out quite easily. Its actually not a ball inside, its a 1/4" diameter needle and seat. I cleaned everything in brake cleaner, greased with a light oil, reassembled.

Outcome? The solenoid works reliably up to 22in of vacuum, and works with 28in of vacuum with a quick tap. I'll have one more go at it, but its as ideal as I could hope at the moment. I just need to buck up and order a new one.
 
Pulled it all apart again, did an even better job cleaning. relubed. exact same, reliable at 22in, needs tapped at 25-28in of vacuum. I ordered a new one, should be here in a couple days.
 
I've been driving for a month and a half with the vacuum pump hooked directly to the wastegate actuator. Its far from ideal, but it gets me back and forth to work. I think it will make it another couple days.
 
That is why some of us have gotten rid of that pesky vacuum system.

You know that there is an alternative to fix it properly.
 
And that solution will be implemented around the time I swap on a different turbo (like an hx40). I just drive 5 miles back and forth to work 99% of the time. I live in Florida, so there are not even hills on the way. Stock control, with a boost fooler to up everything about 2.5 psi will be just fine for now.
 
thedrip said:
And that solution will be implemented around the time I swap on a different turbo (like an hx40). I just drive 5 miles back and forth to work 99% of the time. I live in Florida, so there are not even hills on the way. Stock control, with a boost fooler to up everything about 2.5 psi will be just fine for now.
Click to expand...

Not if it is not working? LOL!!! Don't ask me how I know.
 
Some of us don't want the alternative. Some of us have the air police overlords and don't want any issues with them. Hence must make the stock setup work the best we can.



I changed my boost solenoid. It had been performing poorly until it finally threw a code. When monitoring boost levels, it would not produce any more than 4psi.

After changing it, no more black smoke on acceleration, a full range of boost levels were seen and the mileage went up a little.
 
Got my new solenoid in the mail today. Installed it, and what do ya know, the pcm correctly controls boost. I still have the 10k resistor inline with the MAP, so it makes about 2.5psi more everywhere than it should, but thats ok. Means an absolute peak of 9.5psi, 3rd gear WOT at 2500rpm. after 3300rpm or so, boost drops off dramatically. As it is programmed to do. boost at 70mph cruise is now a sane 3.5-4psi, instead of 7+ psi it was before.

I will fill it up tomorrow, and will see how the fuel mileage changes when I fill up again, in 4 weeks (short commute, and 4 day work week).
 
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