Busy Weekend

[Ruben911]

This long weekend I plan to catch up on several maintenance and troubleshooting items I have put off for a while. Here is the list:

1. Valve adjustment and verification that I don't have any loose or broken head studs.

2. Oil/filter and fuel filter change

3. Rear ride height adjustment. One side is about 1/2 inch lower than the other.

4. Checking fuel system and control pressures with pressure tester I ordered and should be receiving today or tomorrow. Looking to troubleshoot a hesitation under load I have been experiencing for a long time.

5. Overall CIS checkout and troubleshooting, including looking for leaks.

I have a couple questions before I start:

1. Is it true that only exhaust side head studs break?
2. What are the system and control pressures for a 1976 911s. I found out that my 1976 911 is using a 1977 model fuel pump. Should I compare to the 1976 or 1977 model pressure specs.
3. Any specific tips for testing fuel pressures and what to look for.

Thanks

Ruben
1976 911 2.7L
http://users.adelphia.net/~rubensnr

[Ruben911]

Hey guys, any feedback?. Thanks

[sammyg2]

The only head studs I've ever heard of breaking were the lower or exhaust studs. With your engine I would be more concerned with pulled studs and not broken studs unless the case has inserts installed.

I don't have the system pressures handy so I can't give that info but the 77 vs. 76 fuel pump does not factor in at all. There's a primary fuel pressure regulator that sets the system pressure from the pump. Use the 76 specs.

[Jim Sims]

For 1976 CIS:

Cold control pressure readings: 20 psi at 50F, 32 psi at 75F and 49 psi at 100F; all readings are plus or minus 3 psi

System pressure readings: 65 to 75 psi

Warm control pressure readings: 39 to 45 psi

Rest pressure readings: 16 psi plus or minus 3 psi

Return line fuel flow minimum volume: 850 cc per 30 seconds ('77 is the same as '76).

From Watson's "How to Tune and Modify Bosch Fuel Injection":

Stumble or Sag on Acceleration:

Sticking or Binding Airflow Sensor Plate: If the airflow sensor plate binds on the way up, fuel flow will be limited and the engine will sag or stumble.

Sticking or Binding Control Plunger: If the control plunger binds on the way up, fuel flow will be limited and the engine will stumble or sag.

Incorrect System or Warm Control Pressure: If the system pressure is too high or if the control pressure is too high (high system pressure will usually cause high control pressure) the movement of the control plunger will be limited. The engine will begin to run lean as the airflow increases. A lean engine will sag or stumble on acceleration.

Unequal Injector Flow: Restricted injectors can limit the amount of fuel that can pass through them, limiting power. Flow volumes through injectors should not vary by more than 10 percent.

Watson's book is only $20; I recommend you pick up a copy. Cheers, Jim

[Ruben911]

Thanks for the replies, I will use this info to check the health of my fuel injection system this weekend. I also ordered a couple of Bosch fuel injection books and hope to receive them next week. As far as head studs, I'm hoping that when the engine was last opened up for a complete re-build by the previous owner that the inserts were installed (unfortunatelly, the guy did not keep any records of the re-build). I will check the torque readings of the stud bolts this weekend. Thanks again

[Ruben911]

Well, I just finished preping the car for the valve adjustment tomorrow. I raised the rear, drained the oil and removed the lower valve covers. Good news is that all exhaust side stud bolts and and nuts are intact. However, I noticed that they are loose because I tried to tighten the two on cylinder 5 and I was able to turn them fairly easy without applying too much pressure. Tomorrow morning I'm using the torque wrench to tighten them all to specs. Can someone confirm for me that the torque spec is 22 ft lbs (1976 911 2.7L). I'm hoping that this may explain the vacumn leak that I have suspected all along and which forced me to run a rich fuel mixture (8% CO) to keep the car from sputtering. Thanks

[Jim Sims]

21 to 23 ft-lbs is correct. Jim

[Ruben911]

Quick help needed. First the good news is that all my head studs are intact although I had to tighten them all because they were all loose. At least one full turn on each head bolt. Completed the valve adjustment with no incidents, car should be ready to go.

Now the bad. I hooked up the fuel pressure gauge I just received from JC Whitney and proceded to check system and control pressures. What I get is the following:

system pressure: 93 psi

control pressure: 93 psi

Obviously something is wrong. The system pressure is significantly higher than the 65-75 psi spec and thee is no change in pressure when I let the gas flow back to the WUR.

Two questions:

1. Why is my system pressure so high. Can it be that my car was fitted with a 1977 fuel pump instead of a 76. Are there enough shims in the FD to reduce the pressure this much.

2. Why no change in control pressure? Is it a faulty WUR or blocked return to gas tank

Quick responses are appreciated since I'm in the middle of troubleshooting right now.

Thanks

[GB83SC]

Boy there is a Porsche guy next door !
Ruben : I live in Madison Green in Royal Palm Beach, I would like to meet and check out your 911. Drop me a Email
gtburitica@cs.com

[Jim Sims]

Fuel pumps for '76 and '77 have the same characteristics so I doubt that is your problem.

Incorrect high control pressure has only three possible sources:
restriction in return line between fuel distributor and fuel tank; or a restriction in return line from WUR to the fuel distributor; or a bad WUR.

Hook up the CIS pessure tester with the valve open so the gas can flow to the WUR, jumper the fuel pump so it will run without the engine running; loosen slightly each of the fuel return lines (fire hazard and high pressure fuel!) and watch control pressure. If it drops it means there is a restriction in that line. If no change by opening lines then the WUR is defective and should be replaced.

Cheers, Jim

[Ruben911]

Jim, thanks for the reply. I just tested by disconnecting the return line from the WUR and when I turn the pump on, only drops of gas are coming out even though the gauge still shows 93 psi to the WUR. My question is, can I remove the WUR and open it up to see what the restriction may be. Thanks

[Jim Sims]

I've never opened one up so I can't give you any direct guidance. Others have opened them up and made repairs; do a search using WUR as the key word. If you're sure the problem is the WUR then you would have little to lose. If you can fix it you are ahead and if not you were going to have to replace it anyway. Also, visit the Jim Williams web pages on the CIS system; one of the threads under WUR will give you the address. Cheers, Jim

[Ruben911]

Thanks for the reply. I just took apart the WUR and removed a clogged screen that was preventing flow from the FD to pass to the return line. I re-installed the WUR and here are the new readings:

System Presure: 93 psi

Control Pressure: 48 psi

Looks like the screen was the culprit. I still don't know why my system pressure is so high. I may have to remove spacers from the FD pressure regulator. However, my understanding is that each spacer is worth 2-3 psi so I would have to remove 6 to 7 spacers to get down to 75 psi. Does the FD have that many spacers? Thanks

[Jim Sims]

I just noticed your system pressure is too high also. I should have written for you to check this first. This could also be causing your high control pressure as high system pressure also results in a high control pressure. I would check this before opening the WUR. With the engine shutoff run the fuel pump and loosen the return fuel line; if the system pressure doesn't drop remove the pressure regulator on the side of the fuel distributor, take it apart and clean it with solvent and reassemble; if pressure is still too high then it is likely a problem within the fuel distributor. Jim

[Ruben911]

Halleluyah, I just took the car out for a spin after having adjusted valves, tightening head studs and fixing a fuel pressure restriction in the fuel system and I must have picked up 20-25 HP compared to how it was running before. No hesitation under load either. I no longer have to feather the trottle in order to pick up speed. I can't wait to get it out on the highway tomorrow. I must say, the investment in the JC Whitney fuel pressure tester was definetely worth the money. Thanks for your help.

PS. I will work on figuring out why my system pressure is at 93 psi tomorrow. I plan to remove the pressure regulator and to clean it out.

Thanks again.

[Ruben911]

Is the pressure regulator accessible from outside the fuel distributor? I checked my fuel distributor and I don't dee anything in front or to the side (like shown in Hayne's manual) page 257 items 1 to 6).

[Eagledriver]

Sorry to be the first to mention this but you probably have the classic pulled head studs of the 2.7 engine. The reason the head studs needed to be tightened is because the studs have pulled when the engine was hot. As it cools the cylinders contract and the head studs are left loose. I don't know how long the studs will stay torqued but you may notice a exhaust leak in the future coming out from between the heads and the cylinders. Once this becomes bad enough it should be repaired so as not to destroy the mating surfaces on the heads and cylinders. Of course I could be wrong and the studs could've been under torqued in the first place, I hope this is the case for you.

[Jim Sims]

Hi Ruben, Received your e-mail but your return address doesn't work; glad you're working out your CIS problems. I'm an ME and I work at the Lab.

Items 1-6 per pg 257 in Haynes make up the fuel pressure regulator. The plug (item 1) has a hex wrenching feature. The plug is on the back of the fuel distributor with the hex pointing to the passenger side. Look near the two hoses on the back side of the fuel distributor; one of these hoses goes to the cold start valve and the other goes to a plastic "T" fitting.

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

Go to CIS components and scroll down to fuel distributor; one can see the hex of the pressure regulator plug at the top right of the first picture.

Take care when removing these parts as they are spring loaded and you don't want to lose them. I don't think Bosch will sell parts to the general public.

Cheers, Jim

[GB83SC]

Hey Ruben,
How did you make out this weekend?
I hope you where able to correct the problem. I asked my son if he had seen a blue 911 in the area,he said no but all his buds at RPB high have told him there is a twin to your dads car in blue running around here.
Can't wait to see it.

[Elombard]

Ruben, ya I think your bumming, I believe those are classic pulled head stud symptoms.