L jet hard/rough start issues? FIXED....
09-15-2011, 10:52 PM
#1
Race Director
Thread Starter
L jet hard/rough start issues? FIXED....
My 84 928 Estate has suddenly developed a no-rough start issue.
Yesterday it was towed back to the race shop (45 miles) for some prep work for our upcoming race....started right up and ran fine...
Today the shop calls and says it won't start unless you give it some throttle....then it runs rough until you let off the gas and it stalls....if you start it without throttle (normal) it will fire briefly (cold start valve) then the rpm drops and it stalls...
With the previous problems I had with the temp II the shop tried jumpering it, but that didn't work...which makes sense since the engine is cold and jumpering would indicate a very hot mixture....
After checking the WSM troubleshooting guide, the AFC XVI relay seemed like the next step...after jumpering that one the car wouldn't fire at all....which seems really odd....since if the relay was working, jumpering it wouldn't change anything?
So I will head up there tomorrow to figure it out......1st on my list is measuring the resistance on Temp II.....then double checking the relay....if that doesn't work I will check fuel pressure.....and the AFM resistance at the L jet connector...after that I dunno
Other ideas? Any spare L jet brains & AFM's somewhere around Sac?
Yesterday it was towed back to the race shop (45 miles) for some prep work for our upcoming race....started right up and ran fine...
Today the shop calls and says it won't start unless you give it some throttle....then it runs rough until you let off the gas and it stalls....if you start it without throttle (normal) it will fire briefly (cold start valve) then the rpm drops and it stalls...
With the previous problems I had with the temp II the shop tried jumpering it, but that didn't work...which makes sense since the engine is cold and jumpering would indicate a very hot mixture....
After checking the WSM troubleshooting guide, the AFC XVI relay seemed like the next step...after jumpering that one the car wouldn't fire at all....which seems really odd....since if the relay was working, jumpering it wouldn't change anything?
So I will head up there tomorrow to figure it out......1st on my list is measuring the resistance on Temp II.....then double checking the relay....if that doesn't work I will check fuel pressure.....and the AFM resistance at the L jet connector...after that I dunno
Other ideas? Any spare L jet brains & AFM's somewhere around Sac?
Last edited by IcemanG17; 09-21-2011 at 06:47 PM.
09-16-2011, 01:44 PM
#6
Race Director
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09-16-2011, 06:01 PM
#8
Race Director
Thread Starter
well its not the relay.....since power is delivered to both pins on the Ljet....The temp II is no quite right....its readings were a bit weird...so it will be replaced...but the car still is very rough to start or flat won't start at all....then it fires and runs like crap at 1/2 throttle, just to stall once throttle is released...
So I checked the resistance values of the AFM at the L jet connector....all are normal except for pin 27 which is the air temp sensor...its far below spec....spec is 4k ohms+ and it was barely 1k....however Mark Anderson said this is normal....
In an effort to fix this quickly...I have a AFM and L jet brain coming 928intl....that plus a new temp II MUST fix it....if not....things will get very interesting
So I checked the resistance values of the AFM at the L jet connector....all are normal except for pin 27 which is the air temp sensor...its far below spec....spec is 4k ohms+ and it was barely 1k....however Mark Anderson said this is normal....
In an effort to fix this quickly...I have a AFM and L jet brain coming 928intl....that plus a new temp II MUST fix it....if not....things will get very interesting
09-16-2011, 06:12 PM
#9
Rennlist Member
The thermotime switch is a common source of no-start and lingering chug start.
Causes flooding IIRC when the switch fails, and they do fail.
I think it causes the cold start valve to stay on.
I've replaced them on both 84 USA cars here. Looks like a thermocouple but its mounted in the water bridge axially, ie, along the line of the torque tube, front to back.
Causes flooding IIRC when the switch fails, and they do fail.
I think it causes the cold start valve to stay on.
I've replaced them on both 84 USA cars here. Looks like a thermocouple but its mounted in the water bridge axially, ie, along the line of the torque tube, front to back.
09-18-2011, 06:03 PM
#10
Race Director
Thread Starter
The thermotime switch is a common source of no-start and lingering chug start.
Causes flooding IIRC when the switch fails, and they do fail.
I think it causes the cold start valve to stay on.
I've replaced them on both 84 USA cars here. Looks like a thermocouple but its mounted in the water bridge axially, ie, along the line of the torque tube, front to back.
Causes flooding IIRC when the switch fails, and they do fail.
I think it causes the cold start valve to stay on.
I've replaced them on both 84 USA cars here. Looks like a thermocouple but its mounted in the water bridge axially, ie, along the line of the torque tube, front to back.
NEXT ?? I did notice in the L jet connector that pin #34 the ground for the auxiliary air valve is missing...nada...nothing....which is odd?
09-20-2011, 09:56 PM
#12
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Brian
How's it going?
The 82 I bought won't start when it's warm so I am interested to know what you find. I am also anxious to go racing so hope you can solve the problem without too much trouble.
Sean
How's it going?
The 82 I bought won't start when it's warm so I am interested to know what you find. I am also anxious to go racing so hope you can solve the problem without too much trouble.
Sean
09-21-2011, 12:51 PM
#13
Race Director
Thread Starter
The new Temp II went in yesterday and didn't help....the brain and AFM show up today....we'll see if its one of those..... If its not an easy fix I will have to take tomorrow off work to head up there for some quality time with a multimeter!
09-21-2011, 06:48 PM
#14
Race Director
Thread Starter
UPDATE:
Parts arrived today......tried plugging in a good L jet brain....nada-nothing
Swapped out the AFM....BINGO we have a winner....runs normal......so the low resistance off of pin 27 (known as temp I inside the AFM) was the culprit.....
Parts arrived today......tried plugging in a good L jet brain....nada-nothing
Swapped out the AFM....BINGO we have a winner....runs normal......so the low resistance off of pin 27 (known as temp I inside the AFM) was the culprit.....