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Smart quod bastardus
 
fredmeister's Avatar
 
Join Date: Oct 2002
Location: Baltimore, MD, USA
Posts: 2,235
Garage
very hot fuse holder for fuel pumps

How hot should the fuse and fuse holder inside the front truck get with the fuel pumps running?

I was taking pressure readings with the CIS gage kit and running the fuel pumps with the electrical connector on the metering plate disconnected and the front fuel pump is very loud. I dont remember hearing it run much last season when i was driving before i started my rebuild.

I felt the fuel pump relays and they are pretty hot but the fuse and the copper holder that they fit into is too hot to touch, it burns my fingers.

This does not seem normal to be so hot, but am looking for advice whether to replace the front pump or not.

The car will not run at idle anymore, but I was attributing this to a bad MSD program since i also installed a prgrammable 6AL2 at the same time and am in the throws of aginy trying to program it. But now I have emulated the stock ignition timing curves and the car runs for about 2 minutes at idle and then it starts to run rough and my AF ratio reading start bouncing all over.

Is this the front pump failing?

Fred

__________________
1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
---"When you're racing it's life! Anything else either before or after, is just waiting"
Old 05-03-2013, 03:58 PM
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Richard930's Avatar
 
Join Date: Feb 2010
Location: Toronto
Posts: 342
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Well, mine almost caught fire last year so that would be too hot! If you haven't already, I would suggest the wiring mod that splits the power supply for the two pumps. There's a very good write up by Paul (shadetree930) "930 fuel pump overload - the solution". After doing this mod my relays are cool, the new fuses are cool, and everything works well, so I'd do this before troubleshooting the pump itself. Costs about $10 for a couple of fuse holders and a half hour of your time. If you've already done this then look at the pumps.
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Richard
1982 930, K27-7200, Ruf wheels, Leask WUR, Tial WG, WEGO IV AFR, RarlyL8 headers & single out muffler, TK I/C
2011 R350 winter beater
2004 BMW R1100S
Old 05-03-2013, 04:26 PM
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Smart quod bastardus
 
fredmeister's Avatar
 
Join Date: Oct 2002
Location: Baltimore, MD, USA
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I wanted to update my original post with more details.

I have installed a Leask modded WUR and also the MSD programmable unit at the same time.

So far I have concentrated on getting a good timing curve programmed and I have been assuming the bad running right off idle is due to the timing not being right.

I have checked the rotor and all wires and they are good. I am running the non resistor rotor and the timing curve I have programmed is exactly the same as from the stock USA distributor curves from the factory manual. Idle timing is 2 degrees BTDC and the MSD unit is retarding total timing from 32 degrees BTDC 30 degrees at idle. Vacuum is 7 psi absolute and 1000rpm.

With the WUR set to 6.4 bar SP and warm control pressure at 3.4bar the idle AF ratio is 13.0 to 1 or so for the first minute or 2 of running. Then it starts to miss and idle speed fluctuates. As soon as I apply any throttle to rev the engine it starts to misfire and stall and backfire while the AF ratio bounces all over going very lean. Eventually the idle drops and the car stalls.

My theory is the front fuel pump is overheating as it runs so the first minute of operation it is fine cause its cool then it starts to heatup and the issue starts. Like I said the wiring in the fuse panel is stock and is very hot to the touch and the front pump seems noisier than I remember last season before it went in storage. I think I can rule out if the MSD unit is at fault now because it appears to be retarding timing according to the programmed curves and I monitor it on my laptop watching the manifold pressure, rpm, and amount of retard real time during this testing.

I have tested the system with the CIS gages installed and noticed the system pressure bounces every so often between 6.0 and 6.4 bar but it never drops to zero or anywhere close to indicate the front pump shutting down. Also the warm control pressure is rock steady during the time when the car is stalling and idle speed fluctuating. I would have suspected the warm control pressure to be fluctuating during this time to explain the AF ratio changes when this is happening. But dont see this.

Question: Can the MSD be misfiring within the distributor cap at idle because of the huge amount of retard at idle 30 degrees that has to be there for vacuum advance and low rpm operation? I read this on the MSD site somewhere and people mention filing the rotor tip to a point to prevent the spark from jumping to the next plug terminal over inside the cap which would fire the wrong cylinder during high retard. I think this is called spark lead or soemthing. Right now the rotor tip is stock and about 1/4 inch in circumference.

Or am I in need of a new front pump?.....I dont like the heat in the fuses and I am going to take voltage drops at the pump terminals today and look into modifying the wiring to the relays to break up the single power source thru fuse #6 into separate lines by adding another fuse block. Like Richard mentioned above. I hate this electrical crap. More mess in the trunk and more confusion.

I really want to rule out the MSD and isolate this to someting else. I dont think the WUR is at fault either but that was modded as well when this whole thing started. I think this might be coincidence as warm control pressure is in the ball park as mentioned and rock steady at 3.4bar.

Thanks for your ideas,
Fred
__________________
1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
---"When you're racing it's life! Anything else either before or after, is just waiting"
Old 05-04-2013, 08:48 AM
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Smart quod bastardus
 
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Join Date: Oct 2002
Location: Baltimore, MD, USA
Posts: 2,235
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Took voltage readings at the front pump terminals after rewiring the front pump relay by separating it from the rear relay and adding an inline fuse. I left the rear relay wired to the fuse panel as it is since this fuse should be capable of supporting one fuel pump now. Wiring runs alot cooler now....in fact it does not even get the fuse holder warm at all. Relays feel cooler as well.

Battery voltage 12.1 volts with car not running. Measured 10.6 volts at the pump terminals. Doesn't seem too badly out of order, did not measure at terminals with car running and alternator charging at 14 volts though.
The front pump body does not feel warm and it doesn't vibrate much, just is very noisy. The rear pump by contrast is so quiet you cannot hear it. Its running cause I felt it vibrating but did not get voltages off this pump.
Car runs for 1-2 minutes after intial start up fine. Then AF ratio meter goes off scale and it eventually stalls.
Am now in the process of draining over 10 gallons of fuel from the tank so I can replace the front pump.....this is fun.

Ordered a new Bosch 044 unit as per other post advice on increasing fuel flow, so maybe this is a good thing in the end considering the engine mods I have made.
This issue better be the front pump cause I am tapped out of ideas.

Any thoughts?

Fred

__________________
1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
---"When you're racing it's life! Anything else either before or after, is just waiting"
Old 05-06-2013, 07:11 AM
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