Strange 77' 911s 2.7L problem

pk 84 911 · 11-01-2006, 06:30 PM

Please help if you can.

I have just had my 2.7 rebuilt 3000 miles ago. Rebuilt heads, line bore, Rings, Clutch, Injectors +++

The problem is since the rebuild It seems to be clogging injectors. I have flushed the tank run Techron concentrate a few times, cleaned the injectors on a bench clean 3 times.
After the Inj clean it runs extremely smooth, not the slightes stumble on take off, after about 10 miles it starts to stumble then gets progressively worse until I clean the inj again. I use Chevron gas.

I know reason would say it is the injectors clogging up again but after this amount of miles and all the flushings you would think that it should have flushed anything out by now.

Has anyone else experiensed this. Does anyone have any other suggestions. It is really affecting my pleasure of driving this awsome car especially after I think of the $7,000.00 I just spent on it.

Thanks

PK
77' 911s
84' 911 Cab

Rouxzy · 11-01-2006, 07:30 PM

You may have rust in your tank. No matter how many times you flush it, you will still have rust coming out. You either need to replace the tank or take it out and seal the tank.
Tom

47silver · 47silver's Garage

I highly doubt that all of your injectors would go bad at the same time.

Since it runs ok at first I would think that it has something to do with the devices that are affected when the engine goes from cold then to warm so i would check in this order.

1. Cold start valve: this works to inject fuel to the system when cold, if it is sticking on then you have too much fuel going to the cylinders via the intake piping. this may be sticking on and flooding the engine. Ok at first not ok when running a bit. i think that you could remove the wire to the valve to test it. This does not supply fuel to the injectors though.

2.air mixture: do a search for dead recogning adjustment if you do not have a meter.

3. Check the pressures from your warm up regulator. This device maintains the proper pressures during warm-up and normal operation. Too high fuel pressure to the injectors means too much fuel for the amount of air this will certainly cause flooding.

4. Points and distributor timing.

If you do not have dirt in the injectors then it should be 1 one of the above
If it is not one of the above then i do not know what it is..

dougcl · 11-01-2006, 07:55 PM

Some shops have a neat device called a "Motor Vac" that does wonders to a dirty injection system.

DYI: You can pull the injectors out of the manifold, stick each one in a different baby bottle (six baby bottles), lift up on the sensor plate, and observe the flow and volume.

Sounds more like a warm/cold running issue. For example, you'll get similar symptoms if the electrical connection to the warm up regulator is not good.

Doug

Paulporsche · 11-02-2006, 07:37 AM

Control pressures/WUR ditto. Points, plugs, wires and dizzy OK?

pk 84 911 · 11-02-2006, 11:31 AM

I should clarify. After about 10 or so miles it gets continually worse all the time not only after it warms up. After a month the car just runs horribly hot or cold until I clean the Injectors again. There is a very noticable difference after the injectors have been cleaned. Hot or cold. I should also mention it also takes 6 to 8 cranks to start each time from cold but only 1 or 2 after the injectors have just been cleaned.

Thanks for your replies.

Paul

superqueso · 12-05-2006, 04:37 PM

I had the same problem with my 2.7, it turned out that there was in fact rust in my fuel tank. I bought a clean used tank, replaced the fuel filter and had the injectors blown out and it lived happily ever after.

CARRERIC · 12-05-2006, 05:19 PM

I bet it's a rusting tank. Send it to Tank Renu.

You can keep checking your fuel filter for rust particles. The rust particles can also clog the filter real good once car is heated up and pressure in the system. It will contaminate your complete fuel injection system.

"rust is the root of all evil for CIS"

PK 77 911 · PK 77 911's Garage

I just cut the fuel filter apart. Spotless. It has to be a build up in the Fuel Distributor. After reading a very good post on the Fuel Distributor I have decided to take it apart and have a go at cleaning it.

Will keep ypu posted.

PK

M.D. Holloway · 12-11-2006, 01:43 PM

PK,
Techron concentrate is a detergent utilizing a primary/seconadry amines (a quatnary cleaner) and they have free radical polymers in them. The problem is, at high concentrations you can get some really nice deposit formation to occur. It would not surprise me that deposits formed. A hot engine would promote faster formations as well. Throw in some yellow metal and a little water and you would have your self one heck of a mess.

I wrote a pretty comprehensive paper on this topic a few years ago. I'll be glad to send it to you if you would like.

911quest · 12-11-2006, 03:09 PM

Have you checked any of the ignition parts caps and wires can do the same thing I would suspect they were new on the rebuild but if not. My did the same thing run like crap etc. I could go back to the engine and wiggle the plug wires and it would start running better just an idea

T77911S · 12-11-2006, 05:46 PM

did u have the problem before the rebuild?
have u checked the spray before and after cleaning to compare?
what are u cleaning them with?
are they new injectors or did u send them off and have them cleaned?
are u seeing anything come out when u clean them?
if u have that much rust in the fuel dist, i would think it would run bad ALL the time no matter what.

CARRERIC · 12-11-2006, 06:29 PM

Just a thought but have you checked your fuel return line to the tank. Make sure it is clear and clean?

CARRERIC · 12-11-2006, 06:31 PM

You may as well spend the money on new injectors. I never thought it was possible to really clean them without the professional equipment.

PK 77 911 · PK 77 911's Garage

I have had the injectors cleaned 3 times since the rebuild which now has 5000km on it. Each time after the injectors have been cleaned it runs perfectly, smooth without a stumble or a miss right from time I let the clutch out. Within about 15 to 20 minutes it starts to stumble, most noticeably off the line. Passengers even notice it.

It did not do this before the rebuild but it needed A rebuild so it did not run that great anyways. The car sat for a wile prior to the rebuild in moisture so the tank could have rusted. I have since had the tank completely cleaned resulting in a clean fuel filter.

It runs okay when driving, just okay, not great. I notice because I am in tune with how the car feels when it is running well. It progressively gets worse until I clean the injectors again.

My mechanic cleans the injectors. It is a preassurised fluid tool. It seems to work for a while.

It is frustrating and thank you all for your comments and advice so far.

Paul