CIS Rookie Questions

[OldTee]

New to CIS. Situation: Was running OK after injector checks and work by a (otherwise) qualified shop. Then after stopping for a few hours It started and ran rough. Only run smoothly above 2500 RPM. Next day engine cold, would fire and run for 3 or 4 seconds then quit. Pumping throttle did nothing.

It is getting fuel to the cold start system so I presume the pump is operating so what is the most logical fault.

Note: Qualifed shop adjusted the valves and checked out the system after this complaint. Cold natured beast that pops for 5 or so minutes. The mechanic suggested it might be the O2 sensor but does a 79SC have one? Said something about a relay but the mechanic mumbled and my old ears missed what he said. Plugs are recent so are the plug wires.

It is going into a different shop on Tuesday and would like to not be hood winked too much!!

[Par911]

My suggestion would be to get the CO checked, it may be off and need tuning. My CO was way off and after it was adjusted smoothened out the idle. John, if you hear a low humming when you turn the key to the first position, then your fuel pump is working. However, I would check the fuel accumulator, and fuel pump just because you never know how old these parts are.

Said something about a relay but the mechanic mumbled and my old ears missed what he said.

The relay that he was talking about was most likely the fuel pump relay in the fuse box under the front hood, it is the red relay in the slot all the way on the left, closest to the windshield. I have a lot of spare ones lying around. Let me know if you want one. Another thing, how old is the battery and what kind is it? I had a battery that wasn't meant for european cars and was too big for my 911. This meant that there was no battery brace holding the battery down to my SC, so when I would go over a bump, the battery would jump around. I replaced the battery with an optima red top, used a battery plate sold by AJ USA and I don't have any more start problems. I will give you a call and stop by some time this week. BTW, do you have a Bentley manual for the SC's, if not I would highly recommend making this purchase. You can check mine out when we meet up. How did the appraisal of the SC go, hopefully he didn't tell you that he needed to keep it overnight.

[MotoSook]

A wrench who suggests a problem with the O2 sensor on a 79SC is not a qualified wrench! Not one for a CIS 911! Go to the other shop. It sounds like the fuel pump is turning, but suggest the shop check the fuel pressures (system, cold, and warm control pressure).

To check the cold pressure, you'll have to leave the car overnight, but if they are not busy, they should be able to check the system, residual and warm control pressure in less than an hour.

Before you go into the shop, you can check your ignition over yourself! Do the obvious. The ignition is not hard to check.

Good luck.

[OldTee]

Pari, That is Tuesday it goes in for the apprasial. I have been doing some debugging. Fuel pump works great. I pulled the air cleaner and pumped the do higgie inside the box, the one under the fuel distributor. Pump came on. Then I tried to start it. It ran for a few more seconds, probably from the fule I heard squishing in the lines. Then dead. I know there is someone out there that can read these notes and say, "hey, its the alti-pen-umbulum thingie located on the third rock from the sun by the green tree!"

[MotoSook]

If the ignition is fine and yuou really want to dig into the world of CIS, turn the idle adjustment screw counter clockwaise. I have a hunch it may be running rich...although, you haven't given much details of the symptoms.

[OldTee]

Souk, thanks. I would bet a Bud and a Blonde that the ignitation is OK. Where is the fuel filter? In fact, I hear the pump but don't know exactly where it is?

[MotoSook]

Go here and read a little. Search this forum also. It will tell you most of what you need to know.

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

The fuel pump is hidden behind a skid plate under the steering rack. I would not go there yet. To adjust the idle mixture, you'll need a long 3mm allen wrench. I have a "L" shaped on from Sears that works better than the T-handle ones recommended by the factory. How to get to it has been discussed, search.

When it's fixed. send the blonde with a Guinness, not Bud.

[Hladun]

I'd start by looking for a vacuum leak, then I'd do a WUR pressure test. Popping suggests lean running (cracked airbox?). Obviously the guy who worked on your car doesn’t have a clue.

[OldTee]

Thanks for the advice.

I am not ready to begin tweeking things just yet. This problem came on suddenly after some high performance stops to burn the rust off the disks. A repeat of symtoms thought fixed. A knowledgable me plus a knowledgable professional mechanic will solve the problem. Don't like the try this, try that method of repair without a through understanding of what "try" means and is intended to do. Also, a physcial examination indicates some worn hoses and perhaps an exhaust leak. Since I don't fully understand the various boxes, attachments, etc I want to wait a while. Some boxes may require replacement, some just (R&R) cleaning. Time is on my side, but when I am finished it will run like a Swiss watch. Engine has a recent top but nothing done to the injection system.

Thanks again.

[Hladun]

Old Tree,

If you didn’t want an answer, why did you waste our time by asking us the question? With the vague and general nature of your problem, all that you could have reasonably expected was what you got.

[nostatic]

any mechanic that mentions O2 sensor around a '79 isn't qualifed. Well, maybe to flip burgers.

My cold blooded problems were fuel pressure issues.

Here's some good info: http://www.pelicanparts.com/911/technical_specs/911_cis_troubleshoot.htm

The Bentley manual is worthwhile too.

[OldTee]

hladun,
Your observations might have been a waste of your time but they were not a waste of mine. It is a learning experience. I am sorry if you felt slighted in some way, I did not mean it so. Thank you for your, and others, for the help. I will report the results of what happens tomorrow and as the project moves forward.
Happy New Year

[stlrj]

You may want to look into your ignition for solutions. It could be something as simple as a bad plug or a plug connector that came loose.

A wise wrench would make sure your ignition was not the problem before getting into complicated and expensive CIS repairs.

How would you feel if you spent hundreds of $s on your CIS, only to find out it was a bad plug?

Joe

[William Miller]

I just noticed that youre local.
I have a few Bosch CIS books you can read. If you really want to learn how it works. The 79 k-basic system is really not that complicated after you understand what parts do what and why.
I also have pressure gauges you can try when your ready.

[Par911]

I hear the pump but don't know exactly where it is?

Hi John, the fuel pump is located underneath the front of the 911(between the front two wheels), behind the fuel tank. To gain access to it, the SC should be jacked up and then you need to get underneath to remove the stone guard by undoing the four mounting bolts. To check the fuel pump you will need an ammeter. One end will connect to the fuel pump and the other will connect between the black disconnected wire and the fuel pump terminal. Fuel pump range is normally in the 4 to 6 amps range. For the CO, with the idle at 900+/- 50rpm the idle mixture(%CO) should be from 1.5 to 3.5%. But to properly adjust the CO, a gas analyzer test equip. must be used so I advise taking the SC to a shop that has the tools to do it. I know a few local places that have the tools. So, how did the appraisal go? Do you think you will buy the SC?

[Par911]

If you didn't want an answer, why did you waste our time by asking us the question? With the vague and general nature of your problem, all that you could have reasonably expected was what you got.

Go easy on the guy, he is a newcomer to the CIS and is just trying to learn more about it. Not everyone who visits this board are experts.

[William Miller]

John I forgot to mention that Matt has a gas anylizer as well and can set it.
Ed, Milk containers? I thought Beck's bottles were the only approved container?

[OldTee]

Follow up. The mechanic had a fight on his hands. After several tries at locating the problem we went back to ground "o". A previous mechanic had cleaned the injectors and adjusted the valves. We checked injectors and found that the spray pattern was ok for a short period after the key was turned on then it started to dribble. Pulled the fuel filter and found a light rust colored mud like residue. We put on a new filter. Same problem. Then we pulled the accumulator and replaced it with a new one. This got us running, albiet rough. We found a air leak on one of the injectors. Reseating fixed that. New spark plugs too.

Now it starts and runs but spits and fires back when cold. Warm begins to run ok. But idle is not steady. There is a sinewave like curve change of 200 rpm. Up and down, up and down. This I think is caused by the rust still in the system blocking a port somewhere.

Intend to test for more intake leaks add injector cleaner and drive it for a while. Some hoses look bad. Also there is a fuel line leak at the tank. Small one, slow but it may be sucking air. Also intend to check pump check valve. Will do as soon as it warms up here a little. Temp is in the 20sF. (left coast don't say anything)

I admit I don't quite know what I am looking at yet, documenatation on order. Observations gratefully accepted.

[Par911]

John I would take my 911 to Matt over at Stuttgart to get my CO level adjusted if I were you. Like Bill said he has a gas analyzer, and it's always good to get a second opinion. He can always help you in locating potential air leaks as he has a wide array of tools.

[Lorenfb]

As has been mentioned in a number of posts above:

CHECK THE FUEL PRESSURES - SYSTEM PRESSURE & CONTROL PRESSURE!

These are VERY critical to a good starting and running CIS car. Your
wrench should have started here.

Good Luck
Loren
'88 3.2