Help!
Thread Starter
Intermediate
Joined: Jul 2005
Posts: 31
Likes: 0
From: 86 911 M491,Taunton,som,uk
Help!
My 86 911 has been off the road now for 3 weeks and summer has nearly passed.
The car developed a missfire when put under load I have checked out the AFM and the ECU has been checked ,new coil, plugs, HT leads, distributor cap and rotor arm, two new flywheel sensors, new cylinder head temp sensor and DME relay. I took the car to my local motorsport garage but they seamed to be getting nowhere and at fifty pounds an hour I decided to take it home and sort it myself. I have checked all the ground connections in case off an earth fault, i have also checked the fuel pump pressure and current draw all ok. However one thing seams strange is that with the fuel level sender removed from the tank and looking inside with the engine running air bubbles are coming from the swirl pot type unit on the fuel return. Surely this is not normal! I have changed the small length of suction hose to the fuel pump feed but this has made no difference. I am now running at off possible options any advice please!!!!!!!
The car developed a missfire when put under load I have checked out the AFM and the ECU has been checked ,new coil, plugs, HT leads, distributor cap and rotor arm, two new flywheel sensors, new cylinder head temp sensor and DME relay. I took the car to my local motorsport garage but they seamed to be getting nowhere and at fifty pounds an hour I decided to take it home and sort it myself. I have checked all the ground connections in case off an earth fault, i have also checked the fuel pump pressure and current draw all ok. However one thing seams strange is that with the fuel level sender removed from the tank and looking inside with the engine running air bubbles are coming from the swirl pot type unit on the fuel return. Surely this is not normal! I have changed the small length of suction hose to the fuel pump feed but this has made no difference. I am now running at off possible options any advice please!!!!!!!
Race Car
Joined: May 2003
Posts: 4,224
Likes: 102
From: SoCal
A misfire under load (it's assumed this occurs @ heavy load) usually results from:
1. weak spark
Since most ignition items have been replaced but not the wires & end connectors,
check them. Check to see that the spark jumps at least 25mm at the coil wire.
2. lean fuel mixture
For this type of problem, the fuel pressure must be monitored at the misfire point.
Do the basics, e.g. monitor the battery voltage when the misfire occurs &
at the DME control unit.
Check here ( www.systemsc.com/diagnostic.htm ) under Poor Running for more info.
1. weak spark
Since most ignition items have been replaced but not the wires & end connectors,
check them. Check to see that the spark jumps at least 25mm at the coil wire.
2. lean fuel mixture
For this type of problem, the fuel pressure must be monitored at the misfire point.
Do the basics, e.g. monitor the battery voltage when the misfire occurs &
at the DME control unit.
Check here ( www.systemsc.com/diagnostic.htm ) under Poor Running for more info.
Thread Starter
Intermediate
Joined: Jul 2005
Posts: 31
Likes: 0
From: 86 911 M491,Taunton,som,uk
To be more specific the engine will run fine for a time at idle and can sometimes be driven for a mile a so until the problem begins, it usually starts to
cut out very gradually and feels like the engine missing then the problem worsens over the next mile or so until any throttle application under normal driving load results in the engine surging until the clutch is depressed and engine is allowed to return to tickover. when the problem is occuring at tickover there is a slight intermitant fluffing and as the revs are increased the fluffing becomes more noticeable, again this is intermittant and somtimes the engine will rev up crisply with no apparent problem.
Does the presence of air bubbles in the fuel return indicate a fueling problem?
cut out very gradually and feels like the engine missing then the problem worsens over the next mile or so until any throttle application under normal driving load results in the engine surging until the clutch is depressed and engine is allowed to return to tickover. when the problem is occuring at tickover there is a slight intermitant fluffing and as the revs are increased the fluffing becomes more noticeable, again this is intermittant and somtimes the engine will rev up crisply with no apparent problem.
Does the presence of air bubbles in the fuel return indicate a fueling problem?
Racer
Joined: Jul 2005
Posts: 489
Likes: 1
From: Maryland
ok my car does the same stuff its a 87. here is what i did the first time, my catolitic converter colapsed. then some one at a shop has disconected my O2 sensor, id say check that out. my car acts iffy under load sometimes too.
