Surging-stumbling 1990 Reatta

[2seater]

The MAF sensors are not interchangeable. The exterior shape and fastening is the same but there are different where they mount into the casting. See below. The 91 sensor is on the right.

 

It is possible that an air leak at the air duct hose could upset the laminar air flow but it is unlikely. Removal of the inlet screen which straightens the air flow has been found to be a source of instability. 

 

[Edsel-to-Reatta]

3 hours ago, 2seater said:

The MAF sensors are not interchangeable. The exterior shape and fastening is the same but there are different where they mount into the casting. See below. The 91 sensor is on the right.

 

It is possible that an air leak at the air duct hose could upset the laminar air flow but it is unlikely. Removal of the inlet screen which straightens the air flow has been found to be a source of instability. 

 

The air inlet screen looks clean, but should I remove the entire assembly and clean the screen with MAF sensor cleaner? Or replace just the sensor or the complete assembly? There are several options on Rock Auto ranging from $49 for an complete assembly to $110 for a complete Walker assembly to sensors only. I don't want to overspend, but I need to get this stumbling issue behind me so I can do a California smog test and registration.

 

Also, where do you recommend connecting a vacuum gauge? The previous owner had the intake manifold gasket replaced. I want to check manifold vacuum. I'm new to the 3800 engine.

[2seater]

I wouldn't replace the whole assembly, just the sensor. If you remove the sensor, there is no reason you can't just spray a bit of cleaner through the screen in place. The screen can also be removed. It is a friction fit in the housing and it is retained by a large snap ring. Unless the screen has visible damage, or is plugged up, I would leave it alone. , 

 

There aren't any unused vacuum connections on the intake except for the large diameter one pointed to the rear from the block on top. It is for a vehicle with vacuum boosted brakes. It can be used if you adapt to it after removing the cap on the line. Because the vacuum block gets brittle with age and heat, I wouldn't try to use one of those ports directly. You can pull the line at the fuel pressure regulator or the vacuum modulator on the transaxle, or the line to the rear that feeds the HVAC system and cruise control as well. You must connect on the engine side of that rear tee as it contains a check valve to retain vacuum with the engine off.

[Edsel-to-Reatta]

36 minutes ago, 2seater said:

I wouldn't replace the whole assembly, just the sensor. If you remove the sensor, there is no reason you can't just spray a bit of cleaner through the screen in place. The screen can also be removed. It is a friction fit in the housing and it is retained by a large snap ring. Unless the screen has visible damage, or is plugged up, I would leave it alone. , 

 

There aren't any unused vacuum connections on the intake except for the large diameter one pointed to the rear from the block on top. It is for a vehicle with vacuum boosted brakes. It can be used if you adapt to it after removing the cap on the line. Because the vacuum block gets brittle with age and heat, I wouldn't try to use one of those ports directly. You can pull the line at the fuel pressure regulator or the vacuum modulator on the transaxle, or the line to the rear that feeds the HVAC system and cruise control as well. You must connect on the engine side of that rear tee as it contains a check valve to retain vacuum with the engine off.

Thanks for the tips. Seems like the vacuum line to the fuel pressure regulator is the easiest to access. Do I need to use a tee so vacuum continues to feel the regulator and my vacuum gauge simultaneously? Or can the regulator operate without vacuum while my gauge is connected to the vacuum line?

[Ronnie]

I would use the hose going to the servo.

Make sure the lines are all good. They are prone to rotting and cracking in this area.

 

[DAVES89]

3 hours ago, 2seater said:

I wouldn't replace the whole assembly, just the sensor. If you remove the sensor, there is no reason you can't just spray a bit of cleaner through the screen in place. The screen can also be removed. It is a friction fit in the housing and it is retained by a large snap ring. Unless the screen has visible damage, or is plugged up, I would leave it alone. , 

 

There aren't any unused vacuum connections on the intake except for the large diameter one pointed to the rear from the block on top. It is for a vehicle with vacuum boosted brakes. It can be used if you adapt to it after removing the cap on the line. Because the vacuum block gets brittle with age and heat, I wouldn't try to use one of those ports directly. You can pull the line at the fuel pressure regulator or the vacuum modulator on the transaxle, or the line to the rear that feeds the HVAC system and cruise control as well. You must connect on the engine side of that rear tee as it contains a check valve to retain vacuum with the engine off.

I remove the screen and with an old toothbrush and carb cleaner I clean the throttle body and butterfly on both sides.

 At that time I also clean the idle air control and the housing it fits in also using carb cleaner and the toothbrush.

[2seater]

4 hours ago, Ronnie said:

I would use the hose going to the servo.

Make sure the lines are all good. They are prone to rotting and cracking in this area.

 

I do not have my car here to test for certain, but I am pretty sure the vacuum in that area is trapped by the check valve in the tee that connects to the cruise and the HVAC feed. It may be possible the vacuum is only trapped in the HVAC line, but if the reading is modified by the existence of the reservoir, it won't reflect transient changes in the intake manifold vacuum.

[2seater]

4 hours ago, Edsel-to-Reatta said:

Thanks for the tips. Seems like the vacuum line to the fuel pressure regulator is the easiest to access. Do I need to use a tee so vacuum continues to feel the regulator and my vacuum gauge simultaneously? Or can the regulator operate without vacuum while my gauge is connected to the vacuum line?

The fuel pressure will rise to the key on and engine off level, but it will not cause any concern. The base level of three bar (43.5psi) is set by the internal spring pressure, so it cannot increase beyond that.

[Ronnie]

1 hour ago, 2seater said:

I do not have my car here to test for certain, but I am pretty sure the vacuum in that area is trapped by the check valve in the tee that connects to the cruise and the HVAC feed. It may be possible the vacuum is only trapped in the HVAC line, but if the reading is modified by the existence of the reservoir, it won't reflect transient changes in the intake manifold vacuum.

I agree. I was just thinking of an easy place to connect to. My bad.

[Edsel-to-Reatta]

1 hour ago, Ronnie said:

I agree. I was just thinking of an easy place to connect to. My bad.

I teed the vacuum line at the FP regulator - 19" ... is that OK? Car is running great now with new plug wires. Fingers crossed!

Next job is replace the fuel filter. Derdachshund said it's near the left footwell. Is that also the correct location on convertibles? 

[derdachshund]

Just follow the fuel lines either from the tank forward, or the engine back. They're very exposed and easy to see. The car was on drive up ramps when I did mine. Definitely have to crawl under the car.

-derdachshund

[2seater]

11 hours ago, Edsel-to-Reatta said:

I teed the vacuum line at the FP regulator - 19" ... is that OK? Car is running great now with new plug wires. Fingers crossed!

Next job is replace the fuel filter. Derdachshund said it's near the left footwell. Is that also the correct location on convertibles? 

Lines are plastic so it is pretty easy to trace as suggested. 19" of vacuum is very good