Slow to start, perfect idle, won't rev past 1,500 rpm
01-18-2011, 04:55 PM
#1
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Slow to start, perfect idle, won't rev past 1,500 rpm
The car is an 80 U.S. auto.
All this with the fuel pump relay bypassed.
When I am attempting to start the engine, with the fuel pump relay bypassed, I plug in my jumper wire in place of the relay, then turn the key over and attempt to start... it does not fire initially...
However if you turn the key on, pump the gas three times, and give the fuel pump about 2 minutes, it will fire, come up to idle, and idle perfectly. It will idle beautifully forever..
The problem comes in again when you step on the gas... if you attempt to rev the engine above 1,500 rpm it stutters, and makes a pop noise coming from the barn door mechanism....
I have tried a known good barn door intake piece from stan and get the same results.
The fuel filter is clean, I can blow through it both directions.
The fuel pump is a known working pump from a 1983 cis vw rabbit (last check it was pushing 90 psi) and it is of identical fitment to the porsche pump, I have 3 different working pumps including the 928 pump that came with the car and get the same results from all three pumps...
I have just completed a complete top end rebuild with new seals, vac hosing, timing is perfect. It doesn't miss a beat at idle. Plugs are gapped properly, distributor cap is clean, rotor is clean, plug wires are in good shape.
My first reaction to this problem is that it's running lean, or the pump is not delivering enough volume to the engine upon acceleration?
I'm stumped and need some help, I'm pretty sure that three fuel pumps, would not show the identical condition?
My other thought is that I did not have the injectors cleaned.... But if that were the case then why would it idle perfect??
When I bought the car it had this same problem. It had sat for 3 years with a full tank of fuel that had stabil in it. When I finally got all the crap cleaned out of the system it had this identical problem. So that's when I started replacing vac hoses, then ended up pulling the engine and found 7 bent valves. Numerous broken vac hoses etc.
Car in 2009:
Car in October/November 2010:
2nd problem.
As well, on the rear of the auto tranny there are two cut wires that I have yet to be able to identify where they go. They are attached to a plug on the extreme rear of the final drive case, about 1/2 way up on the right side...
pic for reference. They are wrapped in black sheathing and one wire is green and the other is brown.... What do they do and where are they supposed to go??
All this with the fuel pump relay bypassed.
When I am attempting to start the engine, with the fuel pump relay bypassed, I plug in my jumper wire in place of the relay, then turn the key over and attempt to start... it does not fire initially...
However if you turn the key on, pump the gas three times, and give the fuel pump about 2 minutes, it will fire, come up to idle, and idle perfectly. It will idle beautifully forever..
The problem comes in again when you step on the gas... if you attempt to rev the engine above 1,500 rpm it stutters, and makes a pop noise coming from the barn door mechanism....
I have tried a known good barn door intake piece from stan and get the same results.
The fuel filter is clean, I can blow through it both directions.
The fuel pump is a known working pump from a 1983 cis vw rabbit (last check it was pushing 90 psi) and it is of identical fitment to the porsche pump, I have 3 different working pumps including the 928 pump that came with the car and get the same results from all three pumps...
I have just completed a complete top end rebuild with new seals, vac hosing, timing is perfect. It doesn't miss a beat at idle. Plugs are gapped properly, distributor cap is clean, rotor is clean, plug wires are in good shape.
My first reaction to this problem is that it's running lean, or the pump is not delivering enough volume to the engine upon acceleration?
I'm stumped and need some help, I'm pretty sure that three fuel pumps, would not show the identical condition?
My other thought is that I did not have the injectors cleaned.... But if that were the case then why would it idle perfect??
When I bought the car it had this same problem. It had sat for 3 years with a full tank of fuel that had stabil in it. When I finally got all the crap cleaned out of the system it had this identical problem. So that's when I started replacing vac hoses, then ended up pulling the engine and found 7 bent valves. Numerous broken vac hoses etc.
Car in 2009:
Car in October/November 2010:
2nd problem.
As well, on the rear of the auto tranny there are two cut wires that I have yet to be able to identify where they go. They are attached to a plug on the extreme rear of the final drive case, about 1/2 way up on the right side...
pic for reference. They are wrapped in black sheathing and one wire is green and the other is brown.... What do they do and where are they supposed to go??
01-18-2011, 05:15 PM
#2
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The speedometer/odo sensor is mounted in the rear face of the differential housing. The wires go to a connector in the corner of the spare tire well.
01-18-2011, 05:24 PM
#3
Racer
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Wally,
Thanks, I'll go looking again for that connector I think the po cut them off.
Further info on the fuel pump... I tried the pump the car came with and it's part # is 0580464017 - which when I cross referenced the part number is a rebuilt 944 pump that is the same as the original 1980 pumps that porsche was using...
However now after sitting out of the car for a year, the old 928 pump can't keep the engine running.
Thanks, I'll go looking again for that connector I think the po cut them off.
Further info on the fuel pump... I tried the pump the car came with and it's part # is 0580464017 - which when I cross referenced the part number is a rebuilt 944 pump that is the same as the original 1980 pumps that porsche was using...
However now after sitting out of the car for a year, the old 928 pump can't keep the engine running.
01-18-2011, 07:38 PM
#5
Official Bay Area Patriot
Fuse 24 Assassin
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Fuse 24 Assassin
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Just out of curiousity, how do wires look running from the AFM? I had a frayed wire on my 944's harness back in the day that caused the identical issue. It would not go past 1,500 and would either stall out letting off the throttle or idle erratically. Can you verify continuity in the pins to the L-Jet ECU?
