Cough, sputter, cough. Dead fuel pump??

mr.bch · 07-19-2003, 11:07 PM

81 SC 3.0L. Went to start it up to drive to a wedding today and it started fine, but wouldn't rev and wouldn't accept throttle imputs without slight backfiring in the airbox and a general sound of lack of fuel. (Had to drive the VW to the wedding, not nearly as much fun)

Last week my fuel pump started making a real loud whine when ran below 1/2 tank. So, of course, I have kept it above that level since and it has ran fine. After the wedding, I came home and started tring to see what is up. Filled the tank, no change. I can get it to rev up but only after feathering the throttle past it's dead, dry spot of 1000-3500 rpm and with lots of airbox popping. After that, it revs freely in the upper ranges with small throttle openings.

Anyone recognize this symptom? Is my fuel pump not providing fuel? I would think that if it would die, it would die altogether and not provide any fuel. The car is less than 1000 miles off of a valve adjustment and full checkout my the Porsche shop.

If the pump is going to be replaced, what shoudl I replace it with? The $400 Bosch OEM P - pump? The $260 Murray's liftime Carter pump?

k9handler · 07-19-2003, 11:30 PM

rust!

This may not be the case, but it sounds like something is clogging up your fuel filter and possibly the accumulator. In my case the fuel tank was rusted on the inside and rust would clogg up the filter and cause the symptoms you described. Pull your fuel filter and drain it's contents into a container and examine the fuel for foreign matter.

mr.bch · 07-21-2003, 05:59 PM

OK, going off of k9handler's advice and MY83SC's advice also, I am proceeding down the path suggested. Referring to old threads, I know that the old filter is a Bosch 450 905 016, and there are a lot of places who are going to try to sell me a 450 905 079. However, I have a Mahle in there now and it doesn't have a part #. I guess I will go up to my P parts supply place and cross ref some numbers to get what I have now.

So the fuel that came out of the filter is a slight brown color and cloudy. Fine sediment settles when left undisturbed in the jar. So I guess dirty gas has sidelined me. This really clean 911 hasn't been driven much off the person that I recently bought it from out in L.A. There is a (date?) stamp of 22 10 98 on the Mahle! So I will clean the whole fuel system and hope the tank doesn't spit too much rust out.

Question #1: Anyone know how to ID this Mahle filter I have?

Question #2: Is the filter supposed to hook into anything for stability? There is a black semi-circular bracket bolted to my wheel well that also has my ground strap on it. Is the filter supposed to just rest inside that semi-circle? What is this supposed to look like when complete?

Thank you for the help!!

mr.bch · 07-26-2003, 10:45 AM

New fuel pump in and functioning. Screen clean. Inside of tank looks about as clean as it could possibly be. New filter. No leaks anywhere.
And the same symptom persists. Grrr... What now? Start checking every vacuum line in the engine bay? As a precautionary measure, I am going to order up a new relay (red). Maybe pull all injectors and clean? I already took apart the airbox real quick and checked the pop-off valve and everything looked normal.

greglepore · 07-27-2003, 11:01 AM

Have you checked the fuse and holder? I had a recent intermittent starvation problem that acted like a bad pump or filter-the fuse itself turned out the be the problem-one of the "bullet" ends appeared to be making irregular contact. Replaced the fuse, cleaned the contact, and problem solved.

But, not after I drained and flushed the tank and replaced the filter. Check the simple stuff first.

mr.bch · 08-04-2003, 06:52 PM

OK. Update time. (bumpidie bump)

Fuse box connection terminal was (located) and cleaned.

Injectors cleaned, soaked them in carb and choke cleaner over the weekend. New O rings. Reinstalled.

Injectors hum when airbox flapper is moved.

Problem still persists. It almost seems like I have a whole bunch of fouled plugs. Sounds and reacts like a snowmobile after you pipe it and jet it wrong, or trailer a race bike without shutting the fuel off. Sputters when you give it gas, but once it makes it past idle, it revs, albeit, not so cleanly.

Too late tonight to chop the plugs, I guess that falls under the 'simple stuff'. We'll see tomorrow. Car has ran perfectly for 10,000 miles since I bought it

This sux.

Bill Douglas · 08-04-2003, 07:49 PM

Opps

mr.bch · 08-05-2003, 05:22 PM

OK, after a trip to the auto store for correct length sockets and such (grrrr...) and thread searches on best practices on plug chops, here are my pics of the driver's side plugs, both sides. #3 looks really dark and the other 2 are really dark on one side, but the flip side looks decent. How even of a burn does eveyone usually get? Why so dark on one side, because of the offset to the valves?
The plugs in the picture are Bosch Super W5DC's with maybe 1500 miles on them. They replaced NGK BP7ES with unknown mileage. I drove the NGKs from LA to Detroit and then put another 4000 on them. The fuel filter was dated from 98, so I am sure the NGKs weren't new.
Any one with input? I am going to swap in new NGK's tomorrow nite and hook everything back up and start her up and hope. Other than this, I am stumped. Is a visit to the shop to let someone other than me have their way with my baby in my future?

stomachmonkey · 08-05-2003, 06:35 PM

wires

gsxrken · gsxrken's Garage

Make sure the cap and rotor are not too gnarly inside. There can be an ozone tracking build up inside. Could also be a intake leak of some sort, cracked air box or the like. Try spraying propane or ether around the top of the engine and see if the idle picks up any... that is if it will idle. Feel for 'ya, we've all heard the siren call of the shop at the low points of porsche ownership.

mr.bch · 08-08-2003, 05:05 PM

Update:

Cap and rotor are super clean on the inside. Makes a fat spark, too. Wires appear to not be 'leaking' any charge, checked this at night with the lights out.

Changed all plugs to NGK's.

Put in my new red chinese-made fuel pump relay.

Problem persists. I kept the car running till it finally warmed up and once the oil temp dropped closer to '1' at idle, it stopped making the airbox pop and backfires. I was able to take it for a short ride and it seems down on power by 25% everywhere, especially the lower rpms. Once it cleans out and gets over 4000 it revs and pulls, but feels like it is real weak.

Again, I just had the valves done and an inspection <1000 miles ago. Replaced the fuel pump which, by the noises it was making, thought it would be it. New fuel filter. Clean tank screen, clean tank. Clean fuse terminals. Clean the injectors with new O rings. Pop off valve has good seal. No cracks in any intake joints that I can see. Airbox looks like it always does.

What do I check next? Should I replace the fuel accum.? Maybe do something with the cold start injector assembly?
Any suggestions would be GREATLY appreciated. I feel like I am taking stabd in the dark and my short MIchigan summer is dwindling away (sob).

gsxrken · gsxrken's Garage

These things are ignition 9/10ths of the time: CDI, DME, or cap/wires. But let's rule out the fule side of the equation. I know the fuel pump is new but I'd check your fuel pressures. If you had a clogged lines like some on this board who have had to blow out there fuel lines with compressed air, you might have the issues you describe. (Could be the reason your old pump started to fail.) The cold start inj is only on very briefly to get the car started. If it runs better warm than cold, you are lean. If it's running weakly throughout the range, you're probably lean there too.

mr.bch · 08-20-2003, 07:10 PM

bump.

I took her in today.

Couldn't figure it out.

We'll see what happens hopefully tomorrow. PLEASE be easy on my pocketbook.

mr.bch · 08-26-2003, 03:48 PM

I can't believe it.

$400

After checking fuel pressure and vacuum leaks all the stuff I told them I already did, plus a bunch of other stuff.... They noticed the voltage from the OXS sensor wasn't making it to the computer. Long story short...

A new fuse and corrosion cleaned off of the 'interior light, etc, OXS' fuse slot and she runs like a champ.

They did set the mixture correctly and timing, something I couln't do cuz of lack of tools. Also cleaned a bunch of other fuse terminals. Also found out that my alternator isn't charging at idle, but does charge over 1200 rpm. Amazing what $400 gets you.

So moral of this thread is: When checking your fuses, do a THOROUGH job, not a quick 'yup they are there and look good'.

Stay tuned for another thread update that I have going. I am making a complete kit for replacing these fuse blocks with ATC blade fuses and it will look stock and fit under stock cover and be cheap.

Thanks to all for help! I appreciate it. I am going out and driving my baby, now!!!!!!

ruf-porsche · ruf-porsche's Garage

That's is why they get pay the big bucks. Sometime it's just better to bite the bullet and let a professional repair it rather than do the part swap.

Hey I think Souk is having the same problem. Better point him to this thread.

MotoSook · 08-26-2003, 04:24 PM

Checked fuses and wiggled them in case bad cotnacts, but did not clean any yet, but I will. I don't have an O2 sensor tho...thanks.

mr.bch · 08-26-2003, 05:12 PM

One fuse had not blown, and still had both end caps on (so if you did a continuity test it would check out), however, it had burned a ring exactly where it would contact the post that it snaps into. Very deceiving. You couldn't tell unless you pulled it out or tested at the screws.

Until I get my new fuse box kit done, I am going to swap new fuses in and clean all terminals tomorrow.