Tremaine

am driving a ROW 1990 C4 Cab with 115 000 KM on the clock and have the following problems. Unfortunately I stay 1 200 km away from my nearest Porsche Centre and therefore need to do quite a bit of repairs myself.

ALWAYS ON REAR BLOWER FAN
When I turn the ignition to the 1st position (No warning lights on) I can hear the brake pressure pump humming. I normally wait for this to complete before turning the ignition to position 2. As soon as I do this the rear blower fan will come on for 5 seconds, stop for 1 second and then start again. The fan will continue to run when I start the car and will stay on until I switch the car of.

This happens regardless of outside temperature, cold start, hot start or the position of the temperature **** (Blue dot or red dot). I have removed the fan relay and replaced with R04 and R14. No change. I have checked all fuses and still no change. I stay in South Africa and our temperature is normally in the region of 25 degrees.

HUMMING FUEL PUMP
I can hear the fuel pump humming only when I start the car and it keeps humming till I switch off. This seems like an intermittent problem that will sometimes last for weeks and then it will just miraculously stop. I find that whenever the humming noise stops - that the car will have more power and will even idle smoother. I have made a jumper and shorted Pins 3 and 7 of the DME Fuel Pump relay (R41). As soon as I short the pins I can hear the fuel pump working but the car won't start. I suppose a new relay will do no harm.

ERRATIC IDLING / GULPING FOR AIR / BACK FIRING
I notice that the car will idle erratic (more when the engine is hot than cold). If I push the accelerator in fast from idle (in neutral) the car will stall 7 out of 10 times. It sounds like it is gulping for air. (I have drilled the Air box)
I have checked the distributor belt by removing the coil wire from the primary distributor and starting the car. I also did this vice versa and it still starts. I have the "vacuum kit" installed on the distributor.

If I drive in any gear but more specifically in second gear, taking the car slowly to 4000 rpm punching the accelerator but do a slow gear change on 6000 rpm the car will backfire - I can do this at will and would like to know if backfiring is part of the whole experience. Bit annoying at times though.

I have an aftermarket chip installed which is a piggyback chip with its own mappings. I would like to reset the DME by disconnecting the battery but I am not sure how it will influence the aftermarket chip. I will not recommend any aftermarket chips as my fuel consumption is HIGH - 3.8 kilometers per liter traveling long distance (1 200 km) at an average speed of 200 km/h.

I had the car placed on a Dyno and I got the following figures back:
Power 167 kW @ 5788 rpm
Torque 309 Nm @ 4557 rpm

Are these figures in line with what other owners are getting?

I use 98 Octane fuel and stay at the coast.
I also use BP Visco 3000 Premium oil (SAE 20W-50)

I had a compression test done and the following figures came back:
Cylinder 1 - 8.4 bar
Cylinder 2 - 8.4 bar
Cylinder 3 - 8.8 bar
Cylinder 4 - 8.6 bar
Cylinder 5 - 8.1 bar
Cylinder 6 - 8.1 bar

Should I be worried that cylinders 5 and 6 is much less than all the other cylinders.


TIC TIC NOISE
I here a tic-tic noise from the motor when idling or driving - I think this could be tappets - It now sounds just like a VW Beetle (Only looks a lot better).

I would appreciate any help!


Sunny Regards

Steven Terblanche
964 C4 Cab
Jeffreys Bay
South Africa

Arjan B.

First of all.....REMOVE THE DAMN CHIP!!!!!!!!!!

Arjan B.

Now we are talking.

Please do not play with such dangerous chips, get the original one and reset the dme.
I think your ticking noice will be a knock in you cilinders by overheating or bad timing which is performed by the chip.

The need for air is a lack of fuel, which is reckoned by the chip. We don''t know such problems by a stock DME, other then bad ignition coil cables and a possible broken air flow meter. I would guess that by intstalling a stock DME or chip will solve most of the problems. The blower is probable the temp. sender in the blower pipe. They will brake now and then. Mostly the large one is the one who will strike. he small on on top of the pipe is also for your rear blower. By disconnecting the connector, the fan will start running at full speed.

joey bagadonuts

Just to make things a bit easier for fellow readers (and me), let's do the conversion. Your numbers:

Power = 224 hp
Torque = 227 lb ft

I'm assuming these results were obtained from an AWD dyno (two rollers) and measured at the wheels.

Since transmission lost is an inexact science and we're not comparing before and after results, it's hard to say exactly how much over stock your cars is running. But given the Factory flywheel specs (250 bhp and 228 lb ft), I'd say your car shows an improvement vs stock of maybe 15 hp and 30 lb ft of torque.

Good numbers but that 8.9 mpg (3.8 km/liter) figure is a little troubling. It seems you may be running a bit rich. As for the compression numbers, they should be within 15% of each other. Your largest delta is 8.8 vs 8.1, or 8%, which suggests all is well here. If you really want to get a handle on cylinder pressure, have a leak down test performed. Healthy numbers fall in the 3-5% range.

I would have to agree with Arjan on the chip issue. Something doesn't seem right with the air/fuel mix and that's one place to start. Perhaps reinstalling the stock chip will solve the mileage and backfire issues but at the very least, it would eliminate one variable. If problems persists, it seems you'll need to examine all components of the engine management system.
Oh, have you bought Adrian's book? That's probably another good step to take.

JasonAndreas

I've never met a Porsche Fuel pump that didn't hum (just a tiny bit). I've replaced mine twice in 10 years and listened to at least 10 others when I tried to convince the Porsche Regional Rep to replace mine under warranty. You need to check the delivery rate of the pump. On the left side of the engine behind the hot-air blower is the fuel return line. It has a metal/brass colored connector, runs horizontally and will be below all the other lines and next to the oxygen sensor connector (the o2 wire is the only one that runs vertically) It is a LOT easier if you remove the blower. Hook up a longer hose (the thread is M16 x 1.5) to it (when you pull the line, fuel will come out so have something to catch it) and short DME relay pins 3 & 7 (like your already doing) and measure the amount of fuel coming out. In 30 seconds you should have a minimum of 850cm3. Another thing to check for is fuel pressure. (search the archives, i've never done it)

This is could be your fuel pump or your DME relay, etc.

The first thing you should do is replace the aftermarket chip with the stock EPROM if you DO NOT have a MAF. Your problems could all be related to a bad fuel pump, the problem is you don't have a baseline with the aftermarket chip. Who knows how far it advances the timing? Did the chip creator change the timing correction by temperature table in the eprom? etc. etc. You should start with the easiest thing first and that is the custom chip. Theoretically the car should run problem free with the stock chip. If the problems still persist than look at your fuel pump.


Your valves need adjusting. Its not that big a deal if you have a few hours spare time. Most people seem to get hung up on what .1mm feels like with a feeler blade. Living out in the middle of nowhere it would be a good idea to pickup the technical workshop manuals AND Adrian's book. There are also some good web pages floating around with step by step instructions. HERE and HERE

Tremaine

Arjan, Joey and Jason

Thank you for your prompt replies. I have done the following so far:

A - Removed the Aftermarket Chip (Dastek Unichip) by phoning the manufacturer and telephonically bridging out the connector. I then took the car for a drive and noticed that I had quite a bit MORE power in the lower RPM ranges but a bit LESS power over 4000 RPM. I prefer it this way as I use my car as a daily runner. I still noticed the backfire on slow gearchanges and the idling is still not as stable.

B - I did a DME Reset. I started by taking it for a 20 minute drive, returned and disconnected the negative terminal from the battery. I waited 20 minutes (although I do not have an airbag) reconnected and went for a very spirited drive. I live close to a very quite stretch of road and I used all the gears with the entire rpm range. I could not get to the rev limiter in fifth gear but did get a speed of 260 Km/h with the help of a downhill stretch of road. I returned driving "normally". My temperature never got close to the 9 o'clock mark and just went over the 8 o'clock mark. Outside temperature was 24 degrees Celsius.

I restarted the car and still the idling was not very stable - it did get stable after letting the car idle for about a minute. It still backfires and I now smell some (fuel/exhast gasses) in the car. It also still gulps for air if I depress the accelerator fast.

I am going to check the Air Flow Meter and then the delivery rate of the fuel pump.I have also ordered a new DME/Fuel Pump Relay.

I have checked the Temperature Sender (The bottom one with 2 wires connected) in the Rear Blower pipe for resistance and could find no resistance. I unplugged the wires and the fan still runs constantly. I disconnected the top Temperature sender and the fan still runs - I could also find no resistance (I am not sure how to test this one)


Regarding the valve adjustment - I will do that once all the above goes away (I hope?!)


Any feedback would be highly appreciated.

Sunny Regards

Steven Terblanche
964 C4 Cab
Jeffreys Bay
South Africa

Arjan B.

May be you should do the valve adjustment before all the difficult work. Valves of a 911 tend to tight, so the chance of a loss in combustion is there.
A well adjusted valve train and a set of fresh spark plugs is a good start. Then you know your base is ok, and you can continue your logical search.

A DME reset you did is wrong........

Disconnect the battery and wait 10 minutes. Connect the battery, start the car and let it IDLE for 20 minutes! No drives within these time, just after the 20 minutes.
A reset with a absolute nonsens top speed makes no sense.

The fumes of unburned fuel is a high % of unburned HC's and is caused by a bad mixture of fuel, by leaking valves [valve adjstment required] or vacuum leak [s]

Please check your air flow meter as well, as you mentioned by your self. May be someone has on for you to test [15 minutes replace]

# a other thing I have to ask you,: When was you last fill up of your fuel tank? Did the gas station sold you fuel with a too high water % in it or a bad quality of fuel?