rough running 86
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Tuned
Joined: Mar 2003
Posts: 394
Likes: 10
From: austin
rough running 86
The symptoms:
truck broncs and bucks really rough at all rpms, like it's running out of gas.
What I've done:
replaced ignition coil, distributor, ignition control module, set timing to 10 degrees BTDC, replaced TPS, checked fuel pressure at fuel rail (39 psi engine off, 31 psi engine on), checked vacuum lines on EGR valve.
It seemed like it was getting too much air for the amount of fuel it was pumping, so I blocked one of the intake hoses to the throttle body. This improved it slightly by making the bucking less exaggerated, but the problem is still there. All I can figure now is that it's either the MAP sensor, or the EEC-IV. Is there anything else I need to check before buying a non-returnable $50 MAP sensor? Also, pulling the codes only reveals code 44 (thermactor air system error).
TIA,
TM
truck broncs and bucks really rough at all rpms, like it's running out of gas.
What I've done:
replaced ignition coil, distributor, ignition control module, set timing to 10 degrees BTDC, replaced TPS, checked fuel pressure at fuel rail (39 psi engine off, 31 psi engine on), checked vacuum lines on EGR valve.
It seemed like it was getting too much air for the amount of fuel it was pumping, so I blocked one of the intake hoses to the throttle body. This improved it slightly by making the bucking less exaggerated, but the problem is still there. All I can figure now is that it's either the MAP sensor, or the EEC-IV. Is there anything else I need to check before buying a non-returnable $50 MAP sensor? Also, pulling the codes only reveals code 44 (thermactor air system error).
TIA,
TM
Logistics Pro
Joined: Jan 2002
Posts: 3,739
Likes: 3
From: GANS
I wouldn't buy the a MAP sensor before you checked it. If it is similar to a GM, hook a volt meter to the leads of the MAP and it should read steady, and then when you rev the motor (ie less vacuum), the voltage will drop. you'll have to check that in the haynes manual for a ford, (make sure the procedure is the same), but I find, unless there is garbage in the vacuum line, thoses sensors do not normally break.
sounds like you have a big vacuum leak, and that fuel pressure seems a bit low.
sounds like you have a big vacuum leak, and that fuel pressure seems a bit low.
Junior User
Joined: Jan 2004
Posts: 57
Likes: 0
From: Central Texas
Check your TPS... throttle Position Sensor... I am assuming you have EFI .....
This is what tells the computer how much gas to issue to the engine according to the amount the throttle plate is open... it is at the bottom of the throttle shaft.... not very big.... black probably ...
This is what tells the computer how much gas to issue to the engine according to the amount the throttle plate is open... it is at the bottom of the throttle shaft.... not very big.... black probably ...
Thread Starter
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Tuned
Joined: Mar 2003
Posts: 394
Likes: 10
From: austin
thanks for the replies. I had already checked the TPS, it was .93V at idle, and 3.3V WOT. I replaced it, and the WOT is now within specs at 4.5V, but it didn't fix the problem. I forgot to mention in my 1st post that when I set the timing after swapping the distributor, I set it to 10 degrees BTDC, and after I tightened the distributor bolt down, the timing would vary between 6-10 degrees while the truck was just idling. Seemed kind of weird that it would change while idling.
Logistics Pro
Joined: Jan 2002
Posts: 3,739
Likes: 3
From: GANS
Do you have the spout connector unplugged on the dizzy when you check the timing?
If you do, then that indicates you probably need a timing chain.
to find out for sure, (with the engine off) rotate the crank shaft while looking at the rotor inside the distributor cap, if you can turn the crank more than a little bit without have the rotor move, that means there is a lot of slop in the chain or gears (you'll have to move the motor back and forth to see).
forgot to ask, does your 302 have a lot of mileage?
If you do, then that indicates you probably need a timing chain.
to find out for sure, (with the engine off) rotate the crank shaft while looking at the rotor inside the distributor cap, if you can turn the crank more than a little bit without have the rotor move, that means there is a lot of slop in the chain or gears (you'll have to move the motor back and forth to see).
forgot to ask, does your 302 have a lot of mileage?
