Engine Dies when given gas WILL START
12-12-2003, 02:40 PM
#1
7th Gear
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Engine Dies when given gas WILL START
I posted on the forum not too long ago about my problem with the car starting with a bad idle and then slowing dieing out or dieing rapidly when given any throttle. The problem started suddenly with no previous symptoms other than a brief hesitation/stumble when gas was tromped. I came out of a store after shopping and it wouldn't run. This is a 1986 N/A 944. The shop I took it to thought it was the fuel pump. The fuel pump and fuel filter were replaced with no change.
I brought it home and have been checking stuff out on it. I disconnected the fuel line coming to the fuel rail and it was pumping fine. I checked all the vacuum lines on the fuel pressure regulator and dampener. One line was melted so I replaced it with no appreciable change. If I spray a lot of starting fluid into the air filter box it will run fine, but as soon as it runs out of starting fluid and is just running from the gas it acts like it is not getting enough. As I said before as soon as you give it any throttle it will sputter and die. It tends to run on a very low idle around 700- and it wont run longer then 30 seconds before it dies out.
From spraying the starting fluid into the air box I get the impression that the air supply is fine. I also checked the distributor and it is working fine. So the only things I can figure are a senser supplying the computer with information or the fuel pressure regulator/dampener or the computer itself is going.
One other thing to throw in the mix... Everytime I start it it will run for a shorter time before dieing. It won't start at all right now. It wouldn't start at all at the shop before bringing it home, but when I got it home it started up fine although it still had the bad idle and progessively got worse again.
I know this is a lot of information. I'm just throwing it all out for you to process. Hope you guys have some ideas.
I brought it home and have been checking stuff out on it. I disconnected the fuel line coming to the fuel rail and it was pumping fine. I checked all the vacuum lines on the fuel pressure regulator and dampener. One line was melted so I replaced it with no appreciable change. If I spray a lot of starting fluid into the air filter box it will run fine, but as soon as it runs out of starting fluid and is just running from the gas it acts like it is not getting enough. As I said before as soon as you give it any throttle it will sputter and die. It tends to run on a very low idle around 700- and it wont run longer then 30 seconds before it dies out.
From spraying the starting fluid into the air box I get the impression that the air supply is fine. I also checked the distributor and it is working fine. So the only things I can figure are a senser supplying the computer with information or the fuel pressure regulator/dampener or the computer itself is going.
One other thing to throw in the mix... Everytime I start it it will run for a shorter time before dieing. It won't start at all right now. It wouldn't start at all at the shop before bringing it home, but when I got it home it started up fine although it still had the bad idle and progessively got worse again.
I know this is a lot of information. I'm just throwing it all out for you to process. Hope you guys have some ideas.
12-12-2003, 03:06 PM
#2
Burning Brakes
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Well, if it runs on starting fluid, then you have pretty much narrowed the problem down to the fuel system.
I wonder if you have a torn diaphragm in your fuel pressure regulator, and therefore have very low fuel pressure.
What I suspect is happening is that when you first start up on a cold engine, the wider injector pulses deliver enough fuel to let the engine start and run, although not too well. As the engine warms up and the pulses get shorter, the low fuel pressure means not enough fuel gets delivered to the engine. So it quits. Now the engine is partially warm, so the injector pulses shorten much sooner on restart, and the engine then runs for a shorter period before quitting. And so forth - every time you restart, the engine is warmer so it runs for less time. And eventually won't start at all.
When you hit the gas pedal, the drop in manifold vacuum is supposed to "close off" the fuel pressure regulator and make the fuel pressure jump up proportionally to feed the increased fuel demand of the engine. If this doesn't happen because the diaphragm is ruptured, the engine will stall instantly when you hit the gas pedal.
This would also explain why the problem happend gradually. First the diaphram tore a little, so the regulator sorta worked but not that well. Then it tore the rest of the way and is now shot.
If you can, check the fuel pressure and verify that it's low. Or just take a shot and replace the fuel pressure regulator.
Bryan
I wonder if you have a torn diaphragm in your fuel pressure regulator, and therefore have very low fuel pressure.
What I suspect is happening is that when you first start up on a cold engine, the wider injector pulses deliver enough fuel to let the engine start and run, although not too well. As the engine warms up and the pulses get shorter, the low fuel pressure means not enough fuel gets delivered to the engine. So it quits. Now the engine is partially warm, so the injector pulses shorten much sooner on restart, and the engine then runs for a shorter period before quitting. And so forth - every time you restart, the engine is warmer so it runs for less time. And eventually won't start at all.
When you hit the gas pedal, the drop in manifold vacuum is supposed to "close off" the fuel pressure regulator and make the fuel pressure jump up proportionally to feed the increased fuel demand of the engine. If this doesn't happen because the diaphragm is ruptured, the engine will stall instantly when you hit the gas pedal.
This would also explain why the problem happend gradually. First the diaphram tore a little, so the regulator sorta worked but not that well. Then it tore the rest of the way and is now shot.
If you can, check the fuel pressure and verify that it's low. Or just take a shot and replace the fuel pressure regulator.
Bryan
12-12-2003, 03:12 PM
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Race Car
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Check the AFS. When you open the throttle the flap in the AFS has to follow the air flow so the DME will increase the time the injectors open.
If it will idle at all and die when given throttle it's either low fuel pressure or the AFS. Could be the large rubber tube between the throttle and the AFS is split or off. Same as a bad AFS.
Note: You can clean and repossition the wipers inside the AFS. See http://frwilk.com/944dme/afm.htm
If it will idle at all and die when given throttle it's either low fuel pressure or the AFS. Could be the large rubber tube between the throttle and the AFS is split or off. Same as a bad AFS.
Note: You can clean and repossition the wipers inside the AFS. See http://frwilk.com/944dme/afm.htm
12-12-2003, 08:12 PM
#5
Burning Brakes
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check that the barn door in the air flow sensor isn't stuck in the closed position. It's kind of a longshot but I have seen it before. Try unplugging the air flow sensor and see what happens.
12-13-2003, 04:17 PM
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Originally posted by Legoland951
I have plenty of AFS and AFMs. If you are local, come and pick up one of each and buy lunch.
I have plenty of AFS and AFMs. If you are local, come and pick up one of each and buy lunch.
Trending Topics
12-14-2003, 11:07 PM
#10
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Don't count out a vacuum leak. You may have a vacuum line that has finally rotted through or been doing some work under the hood and knocked one adrift.
Neil
90 944S2
Neil
90 944S2
12-14-2003, 11:13 PM
#11
Three Wheelin'
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my vote is for the dme, test one in your car if you can, a freind of mine had the exact same problem, thought it was a cold start issue, starting flid solved it, but it was a pain in the ***. replace that dme, hopefully it will work out.
