85 Carrera fuel starvation

[Andy Minihan]

Hi folks, my 911 won't start, it cranks over perfectly, but doesn't fire.I plugged in my spare dme relay, I then plugged in a friends relay and his dme, from a running 911, still no joy.I pulled out the fuse, looked good, I sprayed the lot with contact cleaner.I then tried to crank it on starting fluid, it fired up for a second and then died.I removed the belly pan and had a pal crank it over while I felt and listened to the pump.it felt as though something was happening, having said that, I don't really know what it should sound like. It never suffered any starting issues before, nor did the pump seem to make any scary noises or clicking noises.what other things should I check before I buy a new pump?.Also I have noticed that bosch pumps range in price from 85 bucks up to 200, even on rock auto,2 seemingly identical parts are wildly different prices, anyone know the reason for the different prices? .I would prefer to buy from our host when ever possible, but I like to research the products a bit first. Thanks

[Adrian M]

Hey Andy,

Don't hesitate, get a new pump and make it a good one.. Price differences may be due to core charge versus no core charge.. Bosche is OEM.. If you have checked the DME and the fuse then one more thing you can do to check for fuel pressure is to remove the black plastic elbow tube between the top of the heat exchanger feed and the blower (the big black tube with flash glare my finger is pointing at in the pic) and then find the cap at the back of the fuel rail (under the elbow tube right where my finger is pointing and I have included a picture of the cap as well). CAREFULLY remove that cap and be aware that there may be fuel pressure and for sure will be a ball bearing in there. Use a rag to catch any fuel and the ball bearing. Put the cap and bearing aside and using a rag to cover, turn the ignition on. There should be considerable fuel pressure. If none or only a dribble or low pressure, you need a pump!

[Adrian M]

Sorry Andy, my message got cut off. It should have ended..

"If none (fuel pressure) or only a dribble or low pressure, you need a pump!"

Cheers,

A.

[Andy Minihan]

ThanKS Adrian, I'll try that tomorrow, and let you know how it went.

[bh912e]

Make sure that you clean the in tank fuel filter before replacing the pump. If your gas tank has corrosion than it will just ruin your new pump.

[DRACO A5OG]

Also when did you replace the fuel filter?

[Scooter]

I had almost the identical problem. Replaced pump and filter together. All was good after.

[scarceller]

Put a fuel pressure gauge at that test port on the LHS fuel rail. Then jumper power directly to the FP fuse up front to force the pump on.

With engine stopped pump running you should have about 3.0bar of pressure.

Don't just change parts, I suggest you verify fuel pressure first.

[Adrian M]

Good advice from all above Andy.. I neglected to tell you that the picture I supplied of the cap with my post is the Fuel pressure test port. My bad. If you have a fuel pressure tester, scarceller's post is good advice. That said, you will know pretty quickly if you have no pressure or just a dribble.

[scarceller]

If you remove that nut on the port be aware it has a steel ball in it that will fall out. Be very careful so the ball does not drop out.

[Andy Minihan]

I loosened the nut and cranked it over, I did not get a pressure gauge yet, there was loads of fuel coming out though.

[Andy Minihan]

I haven't replaced the filter in the past 2 years since I bought it.

[scarceller]

You don't need the exact FP gauge to fit the port as those are expensive. Get any FP gauge and a length of rubber fuel hose and a hose clamp or 2. Just find a hose large enough to slip over the threaded port and use the clamp to keep it tight and in place. The FP in this system is not that high, it's 3.0bar with pump running engine stopped. That's about 42 PSI.

[Andy Minihan]

I checked the fuel pressure at the fuel rail by jumpering the relay,it has 36psi as per the bentleys specs.I guess it must be the crank reference sensor?

[scarceller]

Test the resistance of both sensors, they should read between 900-1100 ohms. The connectors for these are on the bracket on intake runner for cyl #3. On that bracket it will have 3 connectors:
- White one is CHT sensor
- The other 2 are black and are same exact type of sensor, one is ref sensor other is speed sensor. Do NOT mix them up! Test one at a time. They have 3 pins and you are measuring between terminals 1 & 2 for 900-1100 ohms. The terminals are numbered 1,2,3 from bottom to top as they sit in the bracket, so you are measuring from the center to bottom terminal. Any other combo should read infinite resistance. So like this:
- term 1to2 = 900-1100 ohms
- term 1to3 = >100,000 ohms
- term 2to3 = >100,000 ohms

After resistance check you can get a LED 12volt test light (must be LED type) and place the test light across term 1and2 and have someone crank the engine and the light should flicker. The speed sensor will flick plenty since it counts 129 teeth on the flywheel. But the ref sensor only fires 1 time per crank rev so that one may be harder to see.

The other indicator that something is wrong is if the tach needle does not bounce slightly while cranking.

One last test is to be sure the DME is actually alive and running. Do this by turning key to 'RUN' then in the engine bay be sure the IdleControlValve is vibrating and humming. If it's not then the DME is not running program code or has no power. The ICV is right in front of the throttle body, round metal cylinder with 2 hoses attached.

[Andy Minihan]

Ok, I tested them both.The one in the middle of the mounting plate in the engine compartment,which I believe is the speed sensor,did not measure any resistance.I took the icv out and cleaned it,it seems to be humming correctly when I crank her over.

[Discseven]

Originally Posted by Scooter

I had almost the identical problem. Replaced pump and filter together. All was good after.

Slightly different path that you Scott. I replaced fuel & air filter. Good running after that.

[Andy Minihan]

I believe the bmw sensors are cheaper?

[kodioneill]

Originally Posted by Andy Minihan

I believe the bmw sensors are cheaper?

Yes they are, same sensor different name= less expensive.

[scarceller]

If a sensor measured open ckt you need to replace it. Use these from the BMW catalog they work just fine at 1/2 the cost.
Pelican Parts - Product Information: 12-14-1-708-619-M14

Or look around for Bosch #0261210002

I recommend you replace them both while your at it.

I use the BMW sensors all the time, have used them in several 84-89 cars.