1989 Regal 3.1 stalling issue

[Pontiac6KSTEAWD]

I prefer the 2.8/3.1 personally. They are really simplistic engines, although some of the sensors are in stupid locations (Crank Position Sensor for example). I own a 3400 currently (in my Aztek), and its been a good engine for the last 75k miles, no complaints there. But working on that engine in that specific car is a nightmare.

[Sigurd Jarlson]

So I finally had the time and the weather to finish up on this job.
I replaced the following:
The two injectors that ohmed out at 4 and 7
plugs
wires
fuel pressure regulator
MAP sensor
IAC valve
O2 sensor
TPS
Coolant Temp sensor

It started, which is an improvement, but subsequent starts have been hard, and I'm getting a 3-3 MAP sensor code no matter whether I have the original one in or the replacement I bought.
I took it for a shake down run around the block and it really isn't running that well. Hesitation with gas and it seems like it wants to stall when I slow down, but it didn't. 

I don't know what's causing that MAP code. I'm glad it's running again, but despite all the new parts it doesn't seem like it's running as well as it was before the original problem arose.

Thanks for the help.

[55trucker]

If you're still getting the same ECM code 33 with both MAP sensors in place & you know for CERTAIN that there is not a vacuum issue test the circuit from the ECM to the MAP for proper reference voltage & return. A high voltage situation suggests that the ground circuit may have an issue & the return (MAP signal) is seeing too high a return voltage back to the ECM.

 

[Sigurd Jarlson]

So I used an e-cig and found a vacuum leak at the three way check valve that sits under the air filter box. There was a small hole in it, and when I blew smoke into the MAP sensor hose, it poofed right out so I was really hoping that was the issue, but when I put a new one on and fired it up, same thing.

I don't understand why I'm having this issue now, when it was never an issue before I did all the damn work to the car.

I guess the next step is to check the voltage at the MAP sensor as detailed above, but with the clocks changing and the weather turning cold, I'll have a limited window to resolve this.

Thanks
 

 

[Sigurd Jarlson]

So after losing some time due to weather and having to replace the intake manifold gasket on my cousin's S10, I finally got a chance to check my MAP today. Ignition on engine off, both new and old MAP read 4.8V. The connector has good ground and 12V power. When I drew vacuum on both sensors the Volts would go down to less than two. I can't tell you how much vacuum I was drawing, because it's an old brake bleeder pump and the gauge is shot. The vacuum line that connects to the MAP will take a vacuum and hold it when I hook my pump up to it.
With the engine idling, the Voltage on the MAP never went below 4.8V. To me this indicates that the line to the sensor isn't pulling a vacuum correct?

Thanks

[55trucker]

Yeah, looks as tho something is out of kilter there, at idle when the engine is supposed to see full vacuum the MAP voltage back to the ECM should be 1 to 1.5v.

I suggest to you that you pick up another vacuum pump (Harbor Freight?)..don't need to spend an arm & a leg to get one).

Redo the vacuum test with engine running (plug off the manifold port) & note the voltage change on your meter that is supposed to take place as you increase the vacuum pull.

If when doing this you see the proper reaction of the ECM signal voltage to the vacuum changes at the MAP then I would suggest you have a look at the port manifold at the throttle body where the map tube goes to it for leaks.

[Sigurd Jarlson]

I pulled the MAP tube of and with the engine running pulled a vacuum on the sensor and the volts went down and the CEL turned off. It seems like I'm not getting any vacuum at the MAP Tube.
I checked it upstream, but I can't tell where the vacuum is supposed to come from. The MAP line runs across the back of the engine then under the cruise control connects to this 2 way valve.


The line to the cruise control Ts and one line goes to the cruise control and the other goes to what I assume is the vacuum tank. From the cruise control there is a larger rubber line that goes to the firewall.
 

[55trucker]

There should be a vacuum routing diagram stickered to the rad header, is it not there?

 

this is for 91

 

also not this pic is the hvac vacuum reservoir, hidden under the drivers front fender, behind the splash shield, in front of the wheel, it is part of the hvac/cruise vacuum system.

 

[mfewtrail]

You've got the MAP and cruise vacuum lines swapped. Switch those around and you should be good to go.

 

The bottom port on that check valve where you wrote "to cruise and vacuum tank" is the port that goes to the HVAC and to the vacuum ball. There's a t fitting that splits it to the firewall and the ball. The port where you wrote "to line from firewall" should be going to the cruise control unit and then through the firewall. The last port where you wrote "from map sensor" is fed by the second vacuum line(as viewed from the front of the car) on the throttle body(55trucker's diagram shows that part of the circuit). Hopefully that isn't too confusing.

 

 

Edited November 16, 2020 by mfewtrail

[Sigurd Jarlson]

On 11/15/2020 at 11:22 PM, mfewtrail said:

You've got the MAP and cruise vacuum lines swapped. Switch those around and you should be good to go.

 

The bottom port on that check valve where you wrote "to cruise and vacuum tank" is the port that goes to the HVAC and to the vacuum ball. There's a t fitting that splits it to the firewall and the ball. The port where you wrote "to line from firewall" should be going to the cruise control unit and then through the firewall. The last port where you wrote "from map sensor" is fed by the second vacuum line(as viewed from the front of the car) on the throttle body(55trucker's diagram shows that part of the circuit). Hopefully that isn't too confusing.

 

 

You were partially correct, but I had screwed it up even worse than that. In my haste to reassemble, I had left the two lines from the throttle bottle that route underneath the intake manifold and are meant to connect to the MAP and the long hose to the cruise, COMPLETLY UNCONNECTED TO ANYTHING! And buried underneath the throttle cables and such I never noticed and just connected the long line from the cruise to the MAP. I guess I wasn't pumping enough "smoke" into the throttle body lines when I was looking for the leak because it should have been pouring out of those two hoses.
Anyway, I fixed mistake, cleared the codes and she's idling nicely. I haven't taken it for a shakedown cruise yet, but since it was even driving with that crazy vacuum leak earlier, I don't expect any issues.

Thanks for everyone's help with this.
Online car communities like this are an incredibly valuable tool. And I am thankful for them.

[Havoc685]

I'm having issues with a 91 buick regal with a 3.1 it cuts out when I try to pass or floor it once it reaches a certain rpm it dies and I let out it sometime comes back but if not I pull over and start it up and go but does it only when full throttle I've replace wires coils icm I'm at a loss but all those parts was bad but is still doing it very rough idle and is very rich and a dead spot in the throttle as well

[Schurkey]

On 8/21/2024 at 5:24 PM, Havoc685 said:

I'm having issues with a 91 buick regal with a 3.1 it cuts out when I try to pass or floor it once it reaches a certain rpm it dies and I let out it sometime comes back but if not I pull over and start it up and go but does it only when full throttle I've replace wires coils icm I'm at a loss but all those parts was bad but is still doing it very rough idle and is very rich and a dead spot in the throttle as well

The Usual Three:

1. Verify fuel pressure at prime, at idle, and under load. Most fuel pressure gauge assemblies have a push-button pressure release connected to crappy vinyl tubing. Route the tubing so it empties into a drain pan, then push the button while the engine is running. This simulates higher fuel demand if you can't check fuel pressure on the highway. Fuel pressure should remain steady even with fuel flowing down the pressure-relief tubing. How old is the fuel filter? Have you ever dumped a bottle of Chevron Techron Complete Fuel System Cleaner into the gas tank? (Recommended at every oil change.)

2. How old are the usual “tune-up” parts and procedures? Inspect/replace plug wires, spark plugs. Make sure all of the ignition coils will reliably fire a spark-tester calibrated for HEI when the coil is fully warm, and misted with water from a squirt-bottle. Cranking compression test of all cylinders while the spark plugs are removed. Verify EGR, PCV, EVAP, and Heated Air Intake (if used) systems for proper operation. Verify proper initial timing and electronic spark advance. Replace old O2 sensors unless you can PROVE that they're working properly—old O2 sensors get lazy, they don't provide accurate data, but they do provide “data” that fools people into thinking they're “working”.

3. Connect a scan tool (NOT a crappy “code reader”) and look for “codes”. More important, look at the data stream to verify EVERY sensor and computer output. Verify fuel trims during the time that the vehicle is not running properly. Look for misfire counts for each cylinder (OBD2 only.) “Codes” have official diagnostic procedures that will be found in the service manual set for your vehicle.