Could It Be Plugged Injectors?

[Lorenfb]

You definitely have a fuel problem, so don't mess with the CD
unit or you may have two problems.

You may have some fuel contamination which ends up at the
problem cylinders' injectors. You should check the fuel pressure
to be on the safe side.

You need to check the spray when the problem occurs as
many have noted in previous posts. Everyone is generally
right on, so focus on their suggestions.

Good luck
Lorenfb
Systemsc.com

[JTO]

Thanks Loren,

I agree. But, while I'm digging around, I will ensure I'm not getting arcing in the plug wires. I also will probably replace the cheap MotorMeister-supplied wires while I'm at it.

I drove the car last night, and it ran OK until I began to exceed 4000 RPM and more than half throttle. When I first started my drive, the car would accept full throttle and 6000 RPM through third gear maybe twice, then it acted like I had depleted a reserve of fuel somewhere. At this point, it would only accept light throttle applications and low revs. I think there may be some restriction in the fuel flow, maybe from the tank? I don't know yet. I'll fine out though!

Thanks again,
Troy

[masraum]

Hmm, could it be a fuel pressure thing? Could the fuel pump have problems once it heats up?

I agree, it sounds as if it is being starved for fuel when you experience the problem. Maybe you can get a fuel pressure guage on there?

[MotoSook]

Although the 2.7 is a different car...this thread is starting to sound like RazorRacer's thread a while back..but with a twist.

Do you have a vacum guage? Test the vaccum to the distributor/ignition retard when the car is cold, then when the car is warm. It might reveal something...It didn't help me with my ignition problem, but it's a simple test.

I still think this is an ignition problem. If you don't have a vacuum guage or just for grins, try disconnecting and plugging the vacuum line to the dizzy and run the car. I didn't fool around much with my 2.7 motor, so I'm guessing here.

[bigchillcar]

Points. Why hasn't anyone suggested them?! This sounds just like what happens when points start to close. First, the higher rpm driving begins to sputter. At lower rpms (only lightly on the gas) the car seems ok. Eventually, it will start backfiring and sputtering even with light throttle until finally, it won't start anymore. Points closed. See my point?
Ryan

[JTO]

You guys are great. I have received a lot of great ideas from the group on this problem.

The fuel pump might be the culprit. I think its original to the car (almost 30 years!) It is quiet when operating though.

The ignition advance idea is a good one. I will check this too. Thanks.

I know, Noah. I've had my troubles over the last year, especially with MM's tranny. They refunded my money on the tranny rebuild though, so I can't complain too much. The new plug wires are from MM and don't appear to be super great. I have had two people look at them and just say "replace 'em". To remind everyone, I did not know the board, or half of what I know now, when I had MM rebuild the motor. In general, the motor is very powerful (compared to stock) and doesn't leak a drop. Still, if I could do the rebuild over, I'd go with Racer's Group, Factory Tour, Caldwell, or someone else (maybe myself), but I can't go back now.

Lastly, I will look at the entire ignition system, including points, over the next two days, if the family will let me in the garage!

Thanks again everybody. Its like the Porche Collective (you know, the Borg) You guys help me be a better Porsche owner and more self reliant.

Troy

[bigchillcar]

Points, points, points, points, points...oh, ok...you can look at them last...if you have to!
Ryan

[JTO]

Ryan,

What a GREAT IDEA! I'll do it right away!

Thanks!

Troy!

(how's that, a little more enthusiasm!)

[bigchillcar]

Ryan

[RoninLB]

Originally posted by JTO
What a GREAT IDEA! I'll do it right away!

you gotta be kidding.. Why do I assume that people know how to put air in their tires?? .................Ron

[MotoSook]

Geez Ron, now I have to go check my tire pressures..I was wondering why my suspension felt like it was bottoming out! And I just ordered 32 and 45 MM torsion bars for front and rear! (JK)

[speedkillz]

Replace your plugs first. Ngk plugs are smaller than Bosch and don't fit the connector as tight. I had same type of problem. I changed the accum. filter, wires, cap, rotor. ohmed the wires, everything. I didn't change the plugs because they were only 3 weeks old. Changed them and the problem went away.

[Ruben911]

Troy, check my previous two postings titled "Car backfiring at spec CO level" and "Busy Weekend". For a long time I was having a significant engine hesitation, bucking above 3500 rpm. I was able to make the hesitation go away by setting the fuel/air mixture very rich (CO level above 8%). I knew that something else was wrong and that I was just buying time by setting a high CO level until I could find the root cause. Well, this weekend I used a fuel pressure gauge and determined that my WUR had a clogged filter and was not allowing the fuel pressure to drop (control pressure) to allow the fuel mixture to be enriched when I tried to accelerate. So under acceleration the mixture would be too lean and cause the hesitation. I took the WUR appart and removed the little filter and after re-installing it,and adjusting the CO mixture back to specs, the car now pulls great through all rpms with no hesitation or bucking. BTW you can check if your WUR filter is cloggged by disconnecting the return line from the WUR (not the line from the top of the FD to the WUR) and running the pump (engine off, cold, and disconnect WUR electrical plug) to see if gas comes out of the return line. If it does not, it means that the WUR filter or the return line itself is clogged. As always, one must be very careful with testing involving gasoline. Hope this helps.

Ruben
1976 911 s 2.7L

[JTO]

That's a new one Ruben. Thanks. I will do that test when I'm checking the system pressure, etc.

Craig, the plugs may indeed be the problem. I will replace them as part of this work.

Ronin, I was joking with Ryan. I didn't want him to feel like I was ignoring his suggestions!

Thanks all

Troy

[JTO]

Hi Gang,

Today I found that the WUR is not providing fuel pressure to spec. The pressure is about 1/3 it should be when cold. Then, if I jumper around the relay on the side of the engine compartment, I get a pressure of about 2.9 bar (still about half). So, I possibly have a couple of things going on, a bad or plugged WUR and a power issue.

Also, the system pressure bled to zero in about an hour. Either a bad fuel line check valve or a bad accumulator, right?

Ruben, you nailed it! At least part of my problem is the WUR!

Thanks,

Troy

[MotoSook]

Any other numbers for pressure? System pressure? Didn't you have a mechanic test those pressures already?

[Lorenfb]

Did someone mention MotorMeister? My whole evening was ruined.
Rebuilt SC motors for $3000. Barrel and piston sets are about $2500
alone.

Please, no more mention of MotorMeister.

Loren

[Ruben911]

JTO, when I performed the pressure test I looked at two readings. One was system pressure which I tested by using the JC Wittney fuel pressure gauge with the WUR valved off. The other is control pressure which is tested by opening the pressure tester valve and allowing fuel to pass through the WUR. In my case, the system pressure was 93 psi with the valve closed (WUR valved off) and 93 psi with the valve open (WUR in line). This told me that the WUR (or the return line out of the WUR) was clogged. I checked the WUR and that was the culprit with the clogged filter. After removing the filter, and re-testing with the valve open, the control pressure reading was 48 psi. Are you using a pressure gauge setup which allows you to valve off the WUR? If so you need to test for both system pressure and control pressure. Hope this helps.

[JTO]

Hi Ruben,

Where is this filter? I don't want to rip into the WUR with no idea what I'm in for!

Thanks,
Troy

[Ruben911]

Look at the following site and find the WUR under CIS Components:

http://members.rennlist.com/jimwms/CIS/CIShome.html

My WUR is the 76-77 Model shown. On top there should be two openings for fuel lines, one coming from the Fuel Distributor (FD) and one going back to the gas tank return line. The filter is inside the WUR just below the coupling for the line coming from the FD. I actually pulled the WUR appart and pushed the filter from the inside of the WUR by applying pressure with a thin metal rod through a small opening. I would not remove the filter unless you can verify first that it is clogged. I did this by taking the WUR appart and blowing through the opening which houses the filter. I could not get air to blow through it. Unless I'm wrong (and someone else please chime in) you should be able to test if the filter is clogged by disconnecting the return line leaving the WUR and running the fuel pump (engine off). If gas comes out the return line (need to have a container to collect the gas) then the filter is ok or partially clogged. If no gas comes out, then you have clogged filter. Hope this helps. Best way to check though is to use the pressure gauge and measuring the system and control pressures. Thanks