Jim_H

A couple of questions

1. Did this happen to pre SC, DR? I think the other guys only had this happen after SC. AFAIK this has only happened to GT's, post SC

2. I had this happen a while back on a trip to SF but a restart didn't help. With much help from Louis I bypassed it. I was told later I was a fool if I didn't reconnect it. But I have no cats, so, what other preventive purpose does this have. Can something catastophic happen if I don't have cats and limp home is bypassed? Does it also monitor head temp.?

3. Bypassing is somewhat of a bitch in the middle of a hail storm with a flashlight in one hand and a cellphone in the other. If you use Dave Bypass even once it will be than worth the cost.

DR

Hi Jim,

> Did this happen to pre SC, DR?

Yes, I have only heard first hand of it happening to stock 928s. I haven't heard of one personally on an SC'd 928. But if the senor is going bad it will not care if you are boosted or not.

HAPPY NEW YEAR TO EVERYONE!!!

mspiegle

I think that's primarilly what it does. If half of your fuel/ignition system isn't working, then you'll have a temperature difference in your heads.

Tony

..i think your right Shane.


Ahhh... Back from the Hoidays and the "Great White North" and dial up.



Any of you guys think about changing your fuel pumps out for somehting with more capacity?

stock delivery is 1250 cm^3/30sec. = .33gal/30sec =.66gal/min
= 39.6gal/hr = 238lb/hr
( i assume this is a "free flowing" figure?)
24...30lb injectors at 100% duty and the required pressures for your hP levels will not be kind to the stock pump.

I bought a Walbro pump but havent put it on yet. I noticed on a few of my Datalogs from the dyno that the fuel pressure on a few was slowly dropping off as the injectors hit 100%. Everyones pump is in a varying state of health, but for peace of mind im swapping mine out, even at the 400rwhp level im at.

Just another idea to toss into the ring

mspiegle

If he wasn't having enough fuel, I would expect that there would be other problems before finding out that your horsepower is mysteriously not going up. Unless.... you only put 100octane in and don't use a wideband sensor for tuning. I suppose that could mask some lean-ness.

DR

>Any of you guys think about changing your fuel pumps out for somehting with more capacity?

We have sold the Bosch Racing Fuel Pump to a few of the boosted 928ers. It is rated at 172L/hr @ 100PSI and I am told pretty much a direct replacement.

Tony

thats appx 45.5 gph or 273lbs/hr for those that dont use liters....thats at 100psi as well!
Whole lotta fuel. Which is a much better option than maxing out the stock pump. ...remember our pumps are 20yrs old in some cases!!
From what ive heard also, It does bolt right in as well

My stock unit started to make some ugly noises when i started to up the pressure.

A quick way to suck up your seat cushion is to have a fuel pump that craps out at 10psi..

all4woody

I will look at changing the fuel pump, after changing to braided hoses, but I have always run rich. I took me forever to adjust it so there wasn't black smoke pouring out WOT. This doesn't mean I am not hitting full capacity with the pump.
Is there any difference between the S4 and GT exhaust manifold? Just asking.
Happy New Year.
Woody

Carl Fausett

I'd be careful with that ... Sort of like dis-abling the knock sensor/igntion control mechanism. I wouldn't recommend it.

According to what I have read, there was a little flurry of Porsche 928 fires in 1985/86 and the factory lost a few cars before they figured it out. A lean condition (caused by any one of several reasons) could super-heat the catalytic converter to the point that the sound-deadening insulation would start on fire.

The dual-egt sensors and the limp-home 4 cylinder mode mode was added to the 928 in response to these car fires. Don't disable it. Get to a qualified mechanic and correct the root cause of the problem.

mspiegle

Isn't this caused by an overly rich condition?

eitherway, make sure the sensors are clean (As suggested earlier in the thread) and the ports that they go into are clean as well.

FlyingDog

With the cat that far back, it has to be rich. Mine lit from being very rich (only 4 cylinders ingniting). What do people do with the EGTs when they install headers?

BrianG

My EGT probes are at the back of the CAT's. I guess if there's a fire in the CAT's that's where the temp would rise fastest/soonest.

What I want to know is how to deal with the probe circuit(s) now that I have the X-pipe installed.

If it's a normally open circuit, then there's no issue, but if it's normally closed, I need to ground the leads.

If it's a typical EGT probe, it acutally produces a current signal of it's own.

Anyone KNOW what the circuit actually reads from these probes?

DR

Actually, Porsche's "immediate" solution to the cat induced fires was replacement of the original Heat Sheild as the original one was not insulated enough to prevent underbody fires.

RECALL: 8901 Date: July 10, 1989

This is to notify you of a voluntary Recall Campaign involving 6905 Porsche 928S and 928 S4 Model Years 1985 to 1987, within the following VIN ranges:

1985 Model 928S - from WP0JB092_FS860061 to WP0JBD92_FS862279
1986 Model 928S - from WP0JB092_GS860061 to WP0JBD92_GS863010
1987 Model 928 S4 - from WP0JB092_HS860061 to WP0JBO92_HS862481

It was determined that the heat shield above the catalytic converter is inadequate under certain circumstances involving engine malfunction. The problem arises where, due to, among other reasons, improper maintenance or repair, such as improperly secured ignition wires, the engine misfires resulting in overheating of the catalytic converter. If this condition is not detected, materials in the vicinity of the catalytic converter including the lines for the automatic transmission fluid could ignite and cause an underbody fire due to insufficiency of the heat shield.

Customer Notification

Porsche Cars North America will notify all known owners of vehicles within the Recall VIN ranges directly by first class mail during the week of July 24, 1989, or as soon as sufficient quantity of parts are at the dealerships. See the copy of customer notification letter that is included. A listing of all vehicles in your area will be sent to you shortly.

Parts Requirement

Parts required to perform this Recall will be shipped to you shortly. An automatic allocation will be shipped to you based on 70% of the vehicles in your area. Additional parts and kits, after the allocation, should be ordered as needed through normal parts channels using the part number or where applicable, the kit number.



The parts required to perform each Recall are, for:

Time Allowance

a) 120 TU for vehicles with manual transmission and vehicles with automatic transmission up to VIN WP0JB092_GS861000.

b) 190 TU for vehicles with automatic transmission from VIN WP0JB092_GS861001.

DR

Brian,

Check the bottom right of "Page 4 Instruments and Indicators" of the 87 Electrical Schematics in the shop manuals for the wiring of that system (Look for "M-193").

In looking at the schematic for your 87 and then 90 (that had the later system) they look to be almost identical. Although the part numbers for your existing temp probes and the later version are different there is a slim possibility they may work OK be relocating them to the EGT ports on your cylinders heads. If they physically fit those ports and you do not receive any errors you could be OK. If you get immediate errors I would guess the "temp range" is different from the later sensors and you would need to use the later sensors instead , Part # 928.606.155.02

BTW, Carl is correct with this statement "Don't disable it. Get to a qualified mechanic and correct the root cause of the problem."

BUT, it should be OK to disable it temporarily in an emergency to get you back on the road. Having one of the bypass relays in your glove box for emergencies could mean the difference between being stuck on the side of the road in the cold of winter, snapping a Torque tube (autos), or an expensive and unnecessary tow/repair bill.

Also of note, I have heard of dozens of failures of this system (89 and up) and every one of them was due to a dirty or faulty sensor, I don't ever recall there being a real issue with the engine that would cause a fire.

Tony

Heres a couple cool shots...