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Old 02-08-2001, 10:25 AM   #1
kastle
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Post more turbo problems

OK, this is a continuation from my last topic, seen <a href="http://www.i-club.com/ubb-files/Forum24/HTML/001082.html" target="new">here</a>. The problem was @ 5000rpm's boost would drop from 5psi to 2psi. We upgraded the turbo on the SVX-T from a T3 to a T4. Same problem occured. We replaced the MAS and the car was fine.

About an hour later, under WOT, the car would bog down and backfire. It almost seemed like the intake was closed. We turned the boost down from 5psi to 2psi. Same thing. We turned off the boost, same problem.

We changed the MAS again, removed the intake totally and nothing changes.

Any thoughts?
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Old 02-08-2001, 11:00 AM   #2
efoo
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the backfiring and bogging sounds like you could be running extremely rich to the point that the engine is almost flooded. are you still on stock injectors? maybe they are maxed out and only fuel pressure is filling the engine, resulting in pooling of fuel behind the valves and uneven distribution - the fuel isn't being sprayed into the cylinder any more, but more like pouring in.

maybe you should pull your injectors and take a look at their condition?

-Edwin
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Old 02-08-2001, 11:13 AM   #3
SteveS
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I think Edwin is on to something.

One other thought, though. Check and make sure none of your intake tract is collapsing upstream of the turbo. Heard of some people having problems along those lines.

Steve
http://www.lagging.com/
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Old 02-08-2001, 11:14 AM   #4
kastle
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Cool

It is a SVX, keep that in mind, but the points are excellent. I was wondering if the injectors might be clogged / hosed, or if I needed to go the route of a RRFPR or S-AFC.
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Old 02-08-2001, 11:35 AM   #5
efoo
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wait, you don't have a RRFPR?

then i'm reversing my position - you're likely just running out of fuel!

i bet that at higher rpms, the fuel demands of the engine simply outstrip whatever the stock injectors can handle

check your fuel pump too. if you haven't upgraded that yet then you probably should.

-Edwin
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Old 02-08-2001, 11:39 AM   #6
kastle
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No rrfpr, stock fuel system.
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Old 02-08-2001, 11:44 AM   #7
Tony
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You do understand the concept of needing to add fuel with the extra air you're putting into the engine right? This goes for superchargers and nitrous too. More oxygen needs more fuel or your aren't doing anything but running your engine dangerously lean.

Tony

Edit: Cnat spel

[This message has been edited by Tony (edited February 08, 2001).]
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Old 02-08-2001, 11:48 AM   #8
svxtrem
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Kastle- I am betting that you are suffering detonation. I believe the first turbo was way too small, probably on both the compressor and turbine side. Now that you have fixed that problem, even though you are seeing the same 7 psi, you are actually seeing a much greater air mass. That backfiring is a symptom of detonation. The fuel pump in the SVX is rated at over 210 lbs/hour. So the pump is NOT the problem. However, those injectors are 275cc JECS jobs that are actually only 260 cc since the SVX regulator is at 38 psi, not 43. Unplug the battery for 3-4 hours to let the ECU reset. You have to get some type of pressure regulator. My calculations are that a true 5 psi of boost will result in 274 hp, which is well over the 258 those injectors will support at 80% duty cycle. Get yourself a good fuel pressure regulator- 5 psi should need about around 50 psi- that will be safe. If you go to 7 psi you will need 60 psi of fuel pressure. However, I would NOT go over 5 psi without an intercooler.

svxtrem
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Old 02-08-2001, 12:54 PM   #9
kastle
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I will be looking to add a RRFPR, like the Bell or Vortech here relatively soon.
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Old 02-08-2001, 08:48 PM   #10
kastle
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Thanks everyone for all of the results. The end game of this is that I will be having the turbo removed from the SVX and ending that endeavor.

Thanks again.
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Old 02-09-2001, 01:32 AM   #11
Tony
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An EGT or A/F ratio gauge would be a good idea so you can tune the RRFPR to the correct mixture.

Tony
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Old 02-09-2001, 01:45 AM   #12
svxtrem
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You need to remember that the ECU timing is NOT setup for the turbo. That means you need an extremely rich mixture to avoid detonation. However, if you have a very good mechanic, here's a trick you can use. The SVX has a line (wire) between the TCU and ECU called the torque sensor switch. In between shifts at less that WOT, the TCU triggers this line. The ECU will then retard timing 10 degrees. This is used to give a smooth shift.

Get yourself one of those electrical boost switches and tie it into that wire. (I can't remember whether it's normally open or normally closed- check it at idle). Then when the car hits the desired switch boost psi, you can trigger the same behavior. The ECU will think you are shifting, retard the spark, and you will be better off.

Oh, in case you're wondering, I've done this before, and when I ignored that backfiring under WOT, I managed to pound out the rod bearing on #5. Detonation is the enemy. Fuel pressure and timing is the cure.

svxtrem
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Old 02-09-2001, 10:25 AM   #13
Tony
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Just giving up? You were 95% of the way there.

Tony
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Old 02-09-2001, 10:34 AM   #14
kastle
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Unhappy

I found that having to replace all emmissions components and the ECU, plus most of the fuel system to be too much for me.
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