code 78

[mobilevet]

Hi,
I'm getting a code 78 (turbo wategate solenoid). It is intermittent at the moment. I was wondering what the implications of this were (besides the obvious possiblity that the solenoid is bad)...

should I jump on the solenoid or are more diagnostics in order?

Don't know if it's related, but I also have a belt chirp that seem to be coming from the area of the vacuum pump.

Thanks.

[Robyn]

Make sure the vacuum is good. 26"HG and steady at the pump.

Remove the belt and spin the pump. It should rotate easily with a slight bit more pressure needed to turn it past the diaphram spring.
The pulley can actually bounce back and forth as you go past the point at which the diaphram is compressed.
Make sure the bearings are not gone and such.

The 78 can also be due to poor vacuum. Be sure you have vacuum at the wastegate too.

If the vacuum readings are low or the needle on the gauge wobbles a lot the pump is junk.


Best

Robyn

[mobilevet]

Hmm... seems that when I had the belt off a while back and spun the pump it was a bit difficult - like, you couldn't just give it a shove and it go around even one time, but then again you could manually turn it all the way around... in other words it had a pretty big "hump" in the turn

Every since then (and with the belt chirp) I've been meaning to check my vac pressures but have not been able to find a vacuum gauge at my local parts shops. I found one in mail order but it was part of a combination package with other stuff that I didn't need... also was about $100... any leads on a cheaper and just as good vac/pressure gauge would be appreciated.

[chickenhunterbob]

. any leads on a cheaper and just as good vac/pressure gauge would be appreciated.

Well, I don't know where you are at, but in Canada, Canadian Tire has a vac gauge for about 20 bucks, if you are in the US, I suspect one can be had for about half that, at least that's the way the price of tools usually works out...

[mobilevet]

I think I've found a vacuum gauge now.... any ideas if I'm in danger of damaging anything if I keep on driving the truck until I get this figured out?
thanks

[Robyn]

The "Hump" in the turn is normal. Its not supposed to spin like a top.
This thing has a cam in it that works a little diaphram and that is what creates the SUCK :)

If the 78 is intermitent easy driving will not hurt just keep an eye out for clouds of black smoke.

Smoke means too much fuel and higher EGT.

Best

Robyn

[mobilevet]

Yes, I understand the "hump" just wanted to be sure that I was evaluating it correctly. Have a vacuum/pressure gauge on the way...

Where do I plug into the vacuum line to check it? T in right at where it exits the vac pump? Other places? Is the procedure to check at an idle, or do I need to run a long hose so that I can check it while running??

I've also been doing a lot of reading about turbos and waste gates, etc. What is the best way to check the "boost pressure" and the exhaust pressure?

Also, how concerned should I be about exhaust temps with a stock set up? I really don't do any towing, mainly just highway use (which makes me wish I didn't have the 4.10s and had a bit higher gear ratio).

thanks

[Robyn]

The T at the pump will work fine. Just be sure you dont have any leaks in the line betwwen the pump and the gauge.
Idle speed is fine.
Pump should be able to pull 26" HG with a steady needle. If the needle readys low as in 15" or lower or the needle wobbles then the pump is junk.

A wobbly needle indicates a failed valve and a low reading is usually a diaphram on its way down the toilet.

Let us know

Robyn

[mobilevet]

Well.... finally got time to check that vacuum and either I did something wrong or there is no vacuum. Best I can see, there is a very short rubber hose coming off of the round part of the vacuum pump (diaphram?) and then another hose coming off and going to the switch/sensor located at the rear right of the motor where from there another hose goes to the turbo. I put a T about 8 inches from the vacuum pump in the hose that goes to the switch/sensor, about where it dives under the thermostat crossover. Since I got nothing (no reading and the gauge does work if I suck on it) I hooked the gauge directly into the previously mentioned hose and still got a goose egg reading.

So, either I've done something wrong or the pump is not working at all.

On a brighter note, (in reference to a previous post "voltage drop") I took both my batteries by and had them checked. They both checked "bad" - but were under warranty so now with two brand new batteries I've got 14.0 V at the hot post on the firewall at idle with no load, and 13.5 V with lights on high beam, blinker, front and rear AC on and the fan going full blast. That's still with my #4 cable connecting the hot posts on the batteries (instead of a "0" size).

The needle on the voltmeter in the truck still drops down two ticks/lines under a load, but I guess what counts is the reading at the post - if that's not right I'll need a little more schooling.

Thanks to all that helped with that little problem, now to figure out what to do about the vacuum....