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niner11's Avatar
 
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1983 SC CIS issue




I haven't posted in forever but I still lurk a lot. Been doing some reading and testing so I would like to try to confirm a diagnosis. (Got to have at least one pic of the car..).

I put the gauges on my 1983 SC the other day:

sytem pressure and control pressures check per the book both hot and cold. The leak down pressures are better than 25psi after 30 minutes too.

Problem I have been having the last year or so is hot summer restarts. Seems like when it does start I have a few dead cylinders until it runs for about 10seconds. To me it is a classic case of vapor lock.

Here is the question: If all pressures and leak down numbers check out would the only thing left be the injectors themselves? If I'm motivated enough its possible to put the CIS gauge on each individual injector and see if one or more is leaking down. I'm just wondering if after 35 years and an engine rebuild if its just time to put new injectors in the car.

Has anyone been down this road lately? Thanks, Chuck

Old 03-15-2017, 02:29 PM
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When or was the fuel pump replaced? Was the original rebuilt or was a new aftermarket fuel pump put in? The reason I ask is because sometimes hot start issues and vapor lock can be attributed to a check valve on the fuel pump.
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Old 03-15-2017, 02:53 PM
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Not sure but if it is only hot starts I would bet it is the fuel accumulator.

I should know because I'm a certified CIS technician (warning I'm not a certified CIS technician).

There is diaphragm inside there when it goes bad the fuel vaporizes and is too hot when it hits the engine, after awhile the fuel pump pumps enough that fuel cools down and can run properly.

My car would barely start when hot, ran like a top cold.
Old 03-15-2017, 03:03 PM
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Thanks for the responses so far. The system pressure checks. Thats just the fuel pump running. It maintains pressure of somewhere around 5 bar on the check.

The control pressure does not bleed down below 25psi or so even after 30 mins so that should prove the accumulator and CIS fuel distributor are not the issue. I opened up the valve on my gauges and even with the line back to the WUR it still holds leak down pressure above 20 psi for 30 mins.

These values should mean that the check valve is good and that the fuel accumulator is as well. I think.

Chuck

Last edited by niner11; 03-15-2017 at 08:39 PM..
Old 03-15-2017, 03:30 PM
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Run some Techron thru it.....may have some balky injectors. I do it twice between oil changes.
Old 03-15-2017, 05:58 PM
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Usual symptoms of a bad fuel accumulator.

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Old 03-15-2017, 07:08 PM
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I read lots of forums and take notes to prep for my eventual projects, but don't comment much. I couldn't help myself, your wheels look stunning particularly with contrasting dark colored car. They appear annodized and who did them?

Well done, that's classic 911! You nailed it!

Good luck resolving hot start issue!

Regards,

Jeff
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Old 03-15-2017, 07:12 PM
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First, thanks for the replies. Techron is a heluva good idea. I'm no expert but if a fuel accumulator is bad then the car shouldn't pass the leak down 20 minute test. Mine did.

Jeff, thanks! I did the wheels myself. You can look up the Bob Tilton technique somewhere on here but it's basically getting the wheels completely polished and then taking a very fine scotch brite pad to dull the aluminum. Just clean with glass cleaner or brake cleaner.
Old 03-15-2017, 07:20 PM
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Old 03-15-2017, 08:15 PM
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As your fuel pressure tests are coming up normal...Search for Lambda hot start problems due to temp sender on passenger side chain case.
I remember reading about it a long time ago.
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Old 03-15-2017, 09:19 PM
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The fuel accumulator and the check valve in the fuel pump are the reason the pressure is normal with the gauges on. A leak in the check valve or a damaged diaphragm would fail the pressure leak down test. As far as your injectors, use the plastic baby bottle rig setup to verify the injectors are good. There is a post I did on using the baby bottles. The idea of using baby bottles came from another poster. It was cheap to buy and easy to setup. Found that most of my injectors leaked and several spray patterns were not good. Replaced all the injectors, I guess after 35 years there reached their end of life.
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Old 03-16-2017, 04:08 AM
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Thanks for the replies.
Old 03-16-2017, 06:34 AM
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check valve at fuel pump.

accumulator is bad if fuel comes out of bottom port.

plugs
old?
take a look at them. look for wet or oily ones.
you could have a leaky injector fouling a plug.

I would verify mixture setting
make sure there are no air leaks.
THEN new injectors might be a good option.
personally I would try testing them myself to see what they are doing, leaky, compare fuel volume. I would try to get them from someone that can test them first. saw a thread where a guy got some injectors that may of had some flow issues.
try flowcontrol (tech).

air leaks is a big one, injector seals, sleeves, manifold leak, rubber boots on manifold. they can make a cylinder run bad.
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Old 03-16-2017, 06:59 AM
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CIS troubleshooting.........

Quote:
Originally Posted by niner11 View Post



I haven't posted in forever but I still lurk a lot. Been doing some reading and testing so I would like to try to confirm a diagnosis. (Got to have at least one pic of the car..).

I put the gauges on my 1983 SC the other day:

sytem pressure and control pressures check per the book both hot and cold. The leak down pressures are better than 25psi after 30 minutes too.

Problem I have been having the last year or so is hot summer restarts. Seems like when it does start I have a few dead cylinders until it runs for about 10seconds. To me it is a classic case of vapor lock.

Here is the question: If all pressures and leak down numbers check out would the only thing left be the injectors themselves? If I'm motivated enough its possible to put the CIS gauge on each individual injector and see if one or more is leaking down. I'm just wondering if after 35 years and an engine rebuild if its just time to put new injectors in the car.

Has anyone been down this road lately? Thanks, Chuck


Chuck,

There are several things that could cause your warm start problem/s. What I did not find in your post were the control (cold and warm) fuel pressures, fuel injector leak/spray pattern test, FD leak test, ignition test, and unmetered air detection. The last one is the most common over-looked problem in CIS troubleshooting. The residual fuel pressure looks good.

CIS does not suffer from vapor lock. This is a myth because gasoline is an incompressible liquid and with a system pressure of 75 psi.or higher (turbo has 95 psi.) Vapor lock problem is a common occurrence in carb system because of the low fuel pressure (5 psi. or less).

Tony
Old 03-16-2017, 09:58 AM
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Tony,

All good points. I'm away this week so I don't have the numbers in front of me right now but the Bentley/CIS Primer numbers for both hot and cold control pressures were spot on when I tested the system with my gauges a few days ago. Completed an FD leak test too. I will check the spark when I get back.

Good info about vapor lock. My thoughts were that if several injectors are leaking down they would not be under high pressure and the fuel in the line would or could turn vapor. Engine runs great cold or hot but this problem presents itself only on a hot day after sitting for 30-45 minutes.

I will also get a vacuum reading and check for unmetered air before testing the injectors themselves.

Thanks everyone for the thoughts
Old 03-16-2017, 12:12 PM
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Techron (the more potent "fuel system cleaner", NOT "injector cleaner") is a good idea, but if you really want to clean the fuel system internals use a can of BG 44k. It's the gold standard for clean up. Just do a search on it and you'll see many great results. It's what most pros use. May not fix your problem but will sure clean it out! Not available
at your local FLAPS but can be found at many pro mechanic shops or on Ebay.
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Old 03-16-2017, 01:27 PM
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Just as a follow up to my original post I wanted to add that it was my fuel injectors causing the problem. ****ty spray pattern from what I saw and I suspected that some were bleeding down before I even took the car apart.

I guess its worth mentioning that all of the CIS components are expensive enough that its important to test everything before buying any parts. My gauges made things reasonably easy. Wound up changing the fuel filter and making the WUR adjustable just in case the 35 year old injectors weren't the problem and I was wrong.

Thanks for all of the suggestions!

Old 04-23-2017, 11:01 AM
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