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1984 944 Rough Idle and Smoke at Cold Start

 
Old 01-06-2019, 08:40 PM
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guytranspo
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Default 1984 944 Rough Idle and Smoke at Cold Start

So, I'm hoping someone can help with this issue.

Our 1984 944 is having the issue of a crazy rough idle and smoke at start up after sitting for a day or more. The rough idle can be overcome by increasing throttle, but it dies once the throttle is released. After it dies, the car won't start unless the throttle is held to the floor. It will eventually fire and run. Once the car is running, it seems fine. I can shut it down and go back hours later and everything is fine. It starts, idles and runs as it should.

The last time I had the issue, I shut it down and pulled the spark plugs. All four were black and wet with fuel.

I know that this all points to a flooded and/or rich environment. I have read other posts that point to leaking injectors flooding the cylinders while the car is sitting for a time. This all makes perfect sense to me, but I pulled the fuel rail and pressurized the system and didn't see any leaks. I also pulled the injectors and cleaned them. They all seemed to function properly. I would seem strange that all four could be leaking.
We've also changed the fuel pressure valve and done fuel pressure and leak down test that show acceptable results.

We've also changed the DME Temp Sensor.

Additionally, there is no sign of a head gasket problem.

I'm baffled and getting frustrated. The car runs great except for this occasional issue.

What do you think? I'd really appreciate any input.

Thank you.
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Old 01-06-2019, 08:58 PM
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Originally Posted by guytranspo View Post
So, I'm hoping someone can help with this issue.

Our 1984 944 is having the issue of a crazy rough idle and smoke at start up after sitting for a day or more. The rough idle can be overcome by increasing throttle, but it dies once the throttle is released. After it dies, the car won't start unless the throttle is held to the floor. It will eventually fire and run. Once the car is running, it seems fine. I can shut it down and go back hours later and everything is fine. It starts, idles and runs as it should.

The last time I had the issue, I shut it down and pulled the spark plugs. All four were black and wet with fuel.

I know that this all points to a flooded and/or rich environment. I have read other posts that point to leaking injectors flooding the cylinders while the car is sitting for a time. This all makes perfect sense to me, but I pulled the fuel rail and pressurized the system and didn't see any leaks. I also pulled the injectors and cleaned them. They all seemed to function properly. I would seem strange that all four could be leaking.
We've also changed the fuel pressure valve and done fuel pressure and leak down test that show acceptable results.

We've also changed the DME Temp Sensor.

Additionally, there is no sign of a head gasket problem.

I'm baffled and getting frustrated. The car runs great except for this occasional issue.

What do you think? I'd really appreciate any input.

Thank you.
Go to Clark Garage on the web. First test is to determine fuel pressure at the rail. Without data, my first guess is the fuel pressure regulator failed closed, high fuel pressure above spec You can do tests per Clark or change parts at random
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Old 01-06-2019, 10:27 PM
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Originally Posted by T&T Racing View Post
Go to Clark Garage on the web. First test is to determine fuel pressure at the rail. Without data, my first guess is the fuel pressure regulator failed closed, high fuel pressure above spec You can do tests per Clark or change parts at random
Thanks for the reply.

I have been using Clark's Garage for years.

The car has a new Fuel Pressure Regulator and the pressure tests check out fine.

That is why I am here looking for help. I've done extensive research and testing, but I've reached an impasse.
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Old 01-07-2019, 01:30 PM
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Originally Posted by guytranspo View Post
Thanks for the reply.

I have been using Clark's Garage for years.

The car has a new Fuel Pressure Regulator and the pressure tests check out fine.

That is why I am here looking for help. I've done extensive research and testing, but I've reached an impasse.
When you say cleaned the injectors, please provide clarification on who and how cleaned.
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Old 01-07-2019, 08:27 PM
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Originally Posted by T&T Racing View Post
When you say cleaned the injectors, please provide clarification on who and how cleaned.
Thanks again for going over this with me.

I cleaned the injectors using pressurized carb cleaner and pulsing the injectors. I flushed them in both directions.
Also, when I put the injectors back on the fuel rail, I pressurized the fuel system and looked for any leaks before I mounted them in the head.
There were no leaks.

Another development with the car happened this morning. It fired up with no issues this morning, so I decided to drive it to work.
I got about 5 miles, and it just died. I coasted to a parking lot and tried to restart it. No go. I could smell plenty of fuel, but nothing. I also felt the DME relay as I turned the key on and as the engine cranked.
There was clicking in the relay in both instances.
We towed the car home, and when I got home a little while ago, I tried the car again. It fired up and did the rough idle and smoke act. I decided to hold the throttle up for a little while to see what would happen.
After about 3 or 4 minutes, the idle instantly calmed and everything seemed fine.

I'm baffled. I'm wondering if it is a DME issue.
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Old 01-07-2019, 08:56 PM
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Originally Posted by guytranspo View Post
Thanks again for going over this with me.

I cleaned the injectors using pressurized carb cleaner and pulsing the injectors. I flushed them in both directions.
Also, when I put the injectors back on the fuel rail, I pressurized the fuel system and looked for any leaks before I mounted them in the head.
There were no leaks.

Another development with the car happened this morning. It fired up with no issues this morning, so I decided to drive it to work.
I got about 5 miles, and it just died. I coasted to a parking lot and tried to restart it. No go. I could smell plenty of fuel, but nothing. I also felt the DME relay as I turned the key on and as the engine cranked.
There was clicking in the relay in both instances.
We towed the car home, and when I got home a little while ago, I tried the car again. It fired up and did the rough idle and smoke act. I decided to hold the throttle up for a little while to see what would happen.
After about 3 or 4 minutes, the idle instantly calmed and everything seemed fine.

I'm baffled. I'm wondering if it is a DME issue.
From my experience, the fuel injectors need to be disassembled, ultrasonically cleaned, and then reassembled. Southbay Fuel Injector Service tested my fuel injectors prior to cleaning for a benchmark, disassembled and ultrasonically cleaned, reassembled, and tested with a before and after report. The cost was less than $100 including shipping. Southbay has a website and their customer service is excellent.
If it was my call, Southbay cleaning and testing is going to remove one big frustration.
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Old 01-07-2019, 09:05 PM
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Originally Posted by T&T Racing View Post
From my experience, the fuel injectors need to be disassembled, ultrasonically cleaned, and then reassembled. Southbay Fuel Injector Service tested my fuel injectors prior to cleaning for a benchmark, disassembled and ultrasonically cleaned, reassembled, and tested with a before and after report. The cost was less than $100 including shipping. Southbay has a website and their customer service is excellent.
If it was my call, Southbay cleaning and testing is going to remove one big frustration.

I appreciate the input. I'll look into Southbay.

Thanks
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Old 01-10-2019, 01:07 PM
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guytranspo,

Sorry, but I don't have any useful suggestions for you at the moment... however, I am having a similar issue and am very interested to know if you find a fix for your problem.

My 944 was doing fine.. then suddenly, it started acting up with a very rough idle..which would resolve on faster throttle settings. Sometime, Often, it will start and run normally, with no issues. Occasionally, it will
Start running rough, and then smooth out after 5- 10 minutes. Once I drove to a store about 4 miles away, and it was running rough... then, when I came out, after about 10 minutes, it started and ran fine. This is a very puzzling problem because it's very unpredictable so far.

I haven't really spent time on trying to solve this problem but hope to in a few weeks when it warms up in Chicago (my garage is unheated), so I am very interested in the resolution you come up with.

Of course I'm wishing you good luck in getting a solution.

Best

WC944
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Old 01-10-2019, 05:39 PM
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guytranspo
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Originally Posted by WC944 View Post
guytranspo,

Sorry, but I don't have any useful suggestions for you at the moment... however, I am having a similar issue and am very interested to know if you find a fix for your problem.

My 944 was doing fine.. then suddenly, it started acting up with a very rough idle..which would resolve on faster throttle settings. Sometime, Often, it will start and run normally, with no issues. Occasionally, it will
Start running rough, and then smooth out after 5- 10 minutes. Once I drove to a store about 4 miles away, and it was running rough... then, when I came out, after about 10 minutes, it started and ran fine. This is a very puzzling problem because it's very unpredictable so far.

I haven't really spent time on trying to solve this problem but hope to in a few weeks when it warms up in Chicago (my garage is unheated), so I am very interested in the resolution you come up with.

Of course I'm wishing you good luck in getting a solution.

Best

WC944
Hopefully, you don’t have to go through everything that I have with the car.
Im happy to share with hope that it helps others.
The problem is that the intermittent nature of my issues make it very hard to diagnose and repair.

My latest attempt to address the issue was to remove and open the DME / ECU. I thought that I boiled it down to the point where it had to be the DME.
Upon inspection, the only negative thing that I found was some white, powdery corrosion (like you’d see on old batteries) in a small area of the board. I cleaned the area very well and closed it up.
I put it back in the car and the car fired right up and ran fine. Not being confident, I waited another day and the car fired right up and sounded fine. I let it idle until it reached full temperature and, still, no issues.
I waited about an hour, fired it up, and went for a 30 minute drive. The car ran great!
I am still not confident that it is solved. I will take another long drive today to see what happens. It seems unlikely, but maybe that corrosion had enough effect to create the intermittent issue.
We shall see.

I’ll report back later.
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Old 01-10-2019, 06:11 PM
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Thanks for the update... I . certainly hope that is the fix for you.. ... ... fingers crossed for you.
Cheers!
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Old 01-12-2019, 12:30 PM
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You might also want to check the throttle air bypass valve. It is supposed to be open at the start, then close off after engine warms up..about 5 minutes. If it's stuck shut or only partially open that could result in arough idle and rich running. It has two connections, one is positive, the other, ground. remove the valve, apply 12 volts to it with some jumpers and peer down inside with a flashlight...watch the valve open and close slowly. It may just need cleaning also. Glad to hear that the cleaning of the DME made some improvement! Good to know!! Thanks for the additional option!
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