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Blitzkrieg
 
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Join Date: Jan 2008
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Super rich!

Not $, but fuel! I went on a local BMW drive and it was about 20-35 degrees out and the car was extremly rich. I have no AFR guage but I used a little over 3/4 tank going maybe 150 miles.

Normal driving it felt fine, but once you tried to get on it at all it felt like it was choking on fuel. I know it's probably a WUR issue, but maybe some one can help narrow it down for me, or point me in the right direction.
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77' 930
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Old 10-12-2009, 10:31 AM
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Unwiredtools.com for a utcis-pt. You will never look back
Old 10-12-2009, 11:13 AM
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WUR may be the issue. Hope you have the gauge to test the control pressures.

One other possibility could be a bad intercooler O-ring causing an air leak. It would be most noticable on boost, as some of the boosted air would escape resulting in very running. Spray some carb cleaner around all sealing junctions (turbo pipe rubber hose couplings as well as IC O-rings) to see if the engine idle changes.

This, all presuming you have an intercooler (sorry, I can't remember which year Porsche started puting an IC on the 930's).
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Mark H. 1987 930, GP White, Wevo shifter, Borla exhaust, stock everything else. The result of a massive Pelicanite good will fire recovery effort. Truely an open book, ready for the slippery slopes to modification.
Old 10-12-2009, 11:52 AM
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Quote:
Originally Posted by 964 T #304 View Post
Unwiredtools.com for a utcis-pt. You will never look back
Definately on the wish list!

Mark it's not intercooled 77', seemed to run out fine when the weather was warm, but once it got cold it went way rich. I would have figured it would run better in the cold weather as the air is denser.

I guess i'll do some checking of the pressures, but I see a digital WUR in my future. Kinda sucked not being able to keep up with the M3's.
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Old 10-12-2009, 12:00 PM
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Originally Posted by jly535 View Post
Mark it's not intercooled 77', seemed to run out fine when the weather was warm, but once it got cold it went way rich. I would have figured it would run better in the cold weather as the air is denser.

I guess i'll do some checking of the pressures, but I see a digital WUR in my future. Kinda sucked not being able to keep up with the M3's.
Probably just a coincidence that it started running rich when it got cold ouside. Something else is obviously haywire.

Do you have power to the electrical plug-in to the WUR (I think the fuel pumps have to be running in order to read any voltage there). Start her up, unplug the connector and check the voltage. Loss of voltage would not allow the WUR to heat up properly and it would stay in a richer cold start mode with lower control pressures. I would definitely start your diagnostics at the WUR. If control pressures check out, then look at the cold start thermotime switch and injector. The 77's don't have any emmissions crap (like a Lambda O2 sensor system) do they?

Ran my '87 up the canyon Saturday morning, probably 35 degrees out max. Crammed a lot of cold air in there and just went like a bat out of hades.
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Mark H. 1987 930, GP White, Wevo shifter, Borla exhaust, stock everything else. The result of a massive Pelicanite good will fire recovery effort. Truely an open book, ready for the slippery slopes to modification.
Old 10-12-2009, 12:47 PM
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Quote:
Originally Posted by mark houghton View Post
Probably just a coincidence that it started running rich when it got cold ouside. Something else is obviously haywire.

Do you have power to the electrical plug-in to the WUR (I think the fuel pumps have to be running in order to read any voltage there). Start her up, unplug the connector and check the voltage. Loss of voltage would not allow the WUR to heat up properly and it would stay in a richer cold start mode with lower control pressures. I would definitely start your diagnostics at the WUR. If control pressures check out, then look at the cold start thermotime switch and injector. The 77's don't have any emmissions crap (like a Lambda O2 sensor system) do they?

Ran my '87 up the canyon Saturday morning, probably 35 degrees out max. Crammed a lot of cold air in there and just went like a bat out of hades.
Well I started and checked voltage and it was .033 volts, I assume it should have 12 volts?
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Old 10-12-2009, 01:33 PM
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Yep, 12 volts would be nice. Hmmm...now to trace back to the source. If you feel industrious, rig up a temporary power source to keep that WUR heated up, take a drive and see how she performs.
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Mark H. 1987 930, GP White, Wevo shifter, Borla exhaust, stock everything else. The result of a massive Pelicanite good will fire recovery effort. Truely an open book, ready for the slippery slopes to modification.
Old 10-12-2009, 01:50 PM
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CIS components are on a daisy chain. If you have a bad wire you can tap into any other device that operated when the key is on.
Another problem could be a leaky WUR diaphragm which will allow fuel pressure drop = rich.
Do you run greater than stock boost?
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Old 10-12-2009, 02:21 PM
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Originally Posted by RarlyL8 View Post
Do you run greater than stock boost?
1 bar, I did get it running right though. I played with the fuel pump relays and swapped fuel relay II, and checked voltage and and got 12 volts. Not sure if this was just a coincendence or not, but it's running right for now.

Thanks, guys.

Now if I could just re-do that BMW drive!
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Old 10-13-2009, 12:26 PM
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Quote:
Originally Posted by jly535 View Post
1 bar, I did get it running right though. I played with the fuel pump relays and swapped fuel relay II, and checked voltage and and got 12 volts. Not sure if this was just a coincendence or not, but it's running right for now.

Thanks, guys.

Now if I could just re-do that BMW drive!
Hmmm....sounds like maybe you had just one fuel pump running due to relay problems, which might also explain why there was no power to the WUR (that's a long shot on my part without tracing schematics). And if you had only one pump running, even intermittently, it could result in lower than normal fuel system pressure, which would in turn throw off your WUR control pressures to be too low...thus too rich.

Or, there is still a German speaking gremlin lurking around the engine bay just waiting to cause havoc again when least expected.

Glad she's running. Get out an enjoy before it starts snowing again...and hopefully not like you Spokanites went through last year.
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Mark H. 1987 930, GP White, Wevo shifter, Borla exhaust, stock everything else. The result of a massive Pelicanite good will fire recovery effort. Truely an open book, ready for the slippery slopes to modification.
Old 10-13-2009, 01:21 PM
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If only one fuel pump is running I really don't think it's going to make the car run richer.
If that was true the flowtech modified fuel heads wouldn't have their system fuel pressure regulators shimmed to raise fuel pressure and people would be lowering their system fuel pressure to get more fuel out of CIS.
Old 10-13-2009, 01:52 PM
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Quote:
Originally Posted by JFairman View Post
If only one fuel pump is running I really don't think it's going to make the car run richer.
If that was true the flowtech modified fuel heads wouldn't have their system fuel pressure regulators shimmed to raise fuel pressure and people would be lowering their system fuel pressure to get more fuel out of CIS.
Good point! Sometimes my logic is illogical. Here's another shot to consider, be it right or wrong:

Maybe the required two pumps has more to do with fuel volume delivery, vs. fuel pressure. Proper system pressure is needed to assure the right control pressures ultimately, which in turn controls how much the metering plate/arm deflects. One pump may provide adequate pressure...but maybe not enough volume? And thus the injectors wouldn't deliver enough fuel due to lower volume????

Just thinking aloud. The Question: Why two pumps in the first place?
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Old 10-13-2009, 02:27 PM
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Crotchety Old Bastard
 
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If the rear fuel pump was not working you would be down on power on boost.
If the WUR was also not energized (all CIS components are daisy chained to the run sequence) then you would also be rich when not on boost. The car would run very badly. Rich off boost and insufficient pressure on boost.

Two fuel pumps are not mandatory for these cars. The fuel delivery system can support twice the stock power level (can you say homologation racing advantage?). The problem with single pump failure is that the failed pump then becomes a drain on the remaining pump. The front pump cannot push enough fuel through the dead rear pump and a dead rear pump cannot pull enough fuel through a dead front pump.
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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
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Old 10-13-2009, 08:33 PM
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Quote:
Originally Posted by RarlyL8 View Post
If the rear fuel pump was not working you would be down on power on boost.
If the WUR was also not energized (all CIS components are daisy chained to the run sequence) then you would also be rich when not on boost. The car would run very badly. Rich off boost and insufficient pressure on boost.

Two fuel pumps are not mandatory for these cars. The fuel delivery system can support twice the stock power level (can you say homologation racing advantage?). The problem with single pump failure is that the failed pump then becomes a drain on the remaining pump. The front pump cannot push enough fuel through the dead rear pump and a dead rear pump cannot pull enough fuel through a dead front pump.
Good explanation. The solution: Plumb a valved shunt around each of the two pumps, so if either one dies you can shunt around it. Or better yet, take the rear pump out and run with just the front (or vice versa) and save the extra one for a spare.
Do both pumps output the same? Doesn't one of them (the front?) have a check valve in it?
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Last edited by mark houghton; 10-14-2009 at 12:50 PM..
Old 10-14-2009, 11:53 AM
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If you can only use one pump it should be the front.
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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
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Old 10-14-2009, 03:10 PM
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