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boosted 89's Avatar
 
Join Date: Nov 2009
Location: Ontario Canada
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fuel cut??

I'm not sure if this really is happening but I seem to get fuel cut usually in fourth and fifth at 1.0 bar. It pulls hard in third, then starts pullling in forth then whamm...brick wall. I wonder if the wastegate is functioning properly or..the 0 degree celsius weather here is causing it to overboost? I don't recall it doing this in Arizona when I test drove it ....I guess I may have to get it tuned for the difference in altitude or baro pressure?...if there is actually any difference between here and there!
Any ideas would be greatly appreciated.

Chris
Old 12-11-2009, 04:18 PM
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Looks like you're in Canada so the air is probably alot cooler than it was in Arizona. This makes the air denser and boost pressure will be a little higher.

The "wham" is your overboost sensor is triggering the yellow safety relay in the engine compartment disconnecting the grounds to the two fuel pump relays in the front of the car shutting off the fuel pumps so the engine isn't damaged by too much boost and detonation.

The factory boost gauge doesn't go higher than 1 bar so you don't know if it's going higher because of a wastegate problem. You need a mechanical boost gauge that goes to 2 bar or 25-30 psi to accurately know.

It could be the wastegate isn't opening because of a leaking diaphram, rust on the valve guide, or the hose that goes to it from the intercooler is leaking, or blown off.

If the cream colored overboost sensor has become oversensitive from age and disconnects the ground to the wire attached to it at .95 - 1bar that will do it too.
Old 12-11-2009, 04:32 PM
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I don't understand how anyone responded before a picture of the car... normally there is a filter for new members = Pictures FIRST... anyway JF gave you a good advise there.
Old 12-11-2009, 06:03 PM
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Miguel, he's already posted a pix of it. And it's a beauty of a slant nose!

It might be the overboost sender on the pop off valve in addition to what JF mentions. The one with the white wire going to it.

Old 12-11-2009, 06:45 PM
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Hey Boosted89,

So as not to be confusing, the wire circled in the picture is the boost sender to the gauge in the tach. Just so happens that the sender as well as the overboost sensor both have white wires going to them, if memory serves me. Look behind the upper left hand corner of the popoff valve manifold thingy for the OB sensor. JF is correct, those things slowly wear out over time and start tripping earlier in the boost than they should. Still, you need to know accurately what your boost is actually doing. Could be it's spiking beyond 1.2 or so and the OB sensor is just doing what it's supposed to do and shutting down the pumps. "Face-in-the-dash" syndrom.
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Old 12-11-2009, 07:05 PM
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In the picture above the yellow box is around the factory boost gauge sending unit.

To help avoid confusion, the cream colored overboost sensor I mentioned before is on the back of the blow off valve manifold.
Using the same picture I drew a faint red arrow pointing at it and you can also see the brown sheathed wire harness leading to it.
The origonal wire has white insulation and it needs to be grounded for the fuel pumps to run.

If you're car has a long neck intercooler that BOV manifold is gone and the sensor(s) are on an end tank, usually in the back.
Old 12-11-2009, 07:07 PM
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OOPS my bad, I missed that one... the filter is definitely off, let it rip.
Old 12-11-2009, 07:17 PM
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Sorry guys. I got it backwards. Here's a better picture of it:

Old 12-11-2009, 07:35 PM
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Sounds like overboost to me too. Just an FYI, you can get an adjustable pressure switch from NAPA. On my old C2T the overboost safety switch kept kicking in at .8 bar. i tried 3 more factory switches with the varying results. I changed the NAPA piece and adjusted it to 1.2 bar and no more problems. Be careful though you do not want to allow any overboost to occur. You will ruin you engine in a nanosecond: broken rings, lands, melted pistons are all possibilities.
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Old 12-11-2009, 10:56 PM
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Thanks again guys for the information. I shall use it wisely and probably hook in a discrete boost guage to make sure of the actual boost level before making any changes. As for boost level..what is the safe range for a stock motor? I believe the compression ratio is rather low..like 7-7.5 to 1??? With that sort of C/R you would think it could handle loads of boost! I usually stuff 20-25 psi down the throat of the GLH with a 8.5 to 1 C/R without hesitation. Whats the difference with the H-6 motors? Like I said previously..I'm just learning about these things!

Chris

And I'll throw in another pic just to keep good.haha
Old 12-12-2009, 04:20 PM
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If you want a really long life, go with .8 bar. A long life would be 1 bar. After that, life gets shorter and expensive.
Old 12-12-2009, 05:24 PM
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