MAP Sensor
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MAP Sensor
My '91 4.0 with 160K miles is backfiring and blowing the vacuum lines off the tree. Does this year have a MAP sensor? I have a sensor that is mounted under the cowling slightly off center towards the driver side. It is covered in black cardboard. I think it is a MAP sensor, but it doesn't have a vacuum line attached. It has a port on the lower left side, but it doesn't look like a line has every been attached. If this is the MAP sensor where does the sensing line attach to the intake?
I'm aslo going to check the following any other suggestions or most likely candidates:
1. Timing
2. Crank posiiton sensor/wiring
3. intake gasket
4. Fuel filter
5. clean tsp and maf
6. vacuum leaks
I'm aslo going to check the following any other suggestions or most likely candidates:
1. Timing
2. Crank posiiton sensor/wiring
3. intake gasket
4. Fuel filter
5. clean tsp and maf
6. vacuum leaks
Postmaster
Joined: Oct 2003
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From: SoCal
I wonder if this could be bacfiring thru an open intake valve. Have you done any testing with a vacuum gauge? Pulled any trouble codes?
Ignition timing might be off. A bad distributor cap -if it has one- or crosfiring plug wires (have you watched it running in the dark? can cause backfiring.
Ignition timing might be off. A bad distributor cap -if it has one- or crosfiring plug wires (have you watched it running in the dark? can cause backfiring.
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Vacuum is running at 22" and is steady untill the rpm changes from a backfire or a misfire. Plugs are new and wires are only two years old. Looked at it in the dark no arcing along the plug wires. Checked the timing today and it is right on and it does advance when you speed up the engine. Check engine light has not come on. Would there still be trouble codes?
Changed the idle control valve, air cleaner, and cleaned the MAF. Sprayed carb cleaner around intake gasket and there was no change in rpm's. No water in the oil or oil in the water.
It mainly backfires after it is warmed up and is under a load. On the express way in OD and below 3K rpms.
Changed the idle control valve, air cleaner, and cleaned the MAF. Sprayed carb cleaner around intake gasket and there was no change in rpm's. No water in the oil or oil in the water.
It mainly backfires after it is warmed up and is under a load. On the express way in OD and below 3K rpms.
Postmaster
Joined: Oct 2003
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From: SoCal
Take a look at the b-2 forum and read the post "computer codes" mrshorty talks about pulling codes even when there is no check engine light. Interesting. Since it only takes a couple minutes to pull the codes, it sure could'nt hurt.
Lead Driver
Joined: Sep 2003
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From: SoCal
Originally posted by Gschroer
It mainly backfires after it is warmed up and is under a load. On the express way in OD and below 3K rpms.
It mainly backfires after it is warmed up and is under a load. On the express way in OD and below 3K rpms.
Another possibility is the TB position sensor. This part can fail, and usually causes stumbling and backfiring when accelerating.
FYI: All the 4 liter engines (from 1990 on) came with EFI and MAF, and did not use MAP sensors to determine manifold pressure. The MAP sensor actually consists of 2 pressure sensors built back to back. One was used as a MAP sensor in those EFI cars without MAF sensors. The other is an atmospheric pressure sensor, so it is just vented to the atmosphere. The EEC still needs that to determine ambient pressure.
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[QUOTE]Originally posted by xlt4wd90
Another possibility is the TB position sensor. This part can fail, and usually causes stumbling and backfiring when accelerating.
Is the TB sensor the same as the TPS, that senses the postion of the throttle? Small black sensor on the right side (facing engine)of the throttle body.
Another possibility is the TB position sensor. This part can fail, and usually causes stumbling and backfiring when accelerating.
Is the TB sensor the same as the TPS, that senses the postion of the throttle? Small black sensor on the right side (facing engine)of the throttle body.
