Pulling my hair out!

[ezlnh8u]

I have been having this running rough and extremely rich issue with my vehicle. I will try to be as detailed as possible with what we have replaced and troubleshooted. (Engine M20 from a 1991 325i)

The car turns on but runs with a surging idle and rich. upon disconnecting the fuel rail where the injectors are and re plugging it back while the car is running, it makes the car run normal. perfect idle and no black smoke.

List of things we have replaced.

1:Plugs/Wires/ Cap & Rotor/Distro
2:ICP/TPS
3:Injectors
4:Swapped 3 different ECU's (Same Number)
5:Replaced TB
6:Coolant Temp Sensor
7:02 Sensor
8:Checked the timing
9:Fuel Pump Checked
10:Smoke test done
11:FPR Replaced

I cant do a stomp test as this is a swap on a 74-2002, the car has been running great for the past 4 years, and from one day to another it developed this issue. (Maybe electrical)? Many thanks for the input.

Edited December 4, 2018 by ezlnh8u

[02Pilot]

What are you unplugging when it's running? Does it happen hot and cold? Does it run better under load, or is it rich regardless?

[ezlnh8u]

7 minutes ago, Andrej said:

What are you unplugging when it's running? Does it happen hot and cold? Does it run better under load, or is it rich regardless?

It runs rich regardless,  I am unplugging the Fuel Rail, this holds all the injectors, If i unplug 2-3 times while the car is idling (I have to hold the throttle) and snap it back in, it seems as if its timed correctly, the car will settle down and idle perfect. 

[ezlnh8u]

 

That fuel rail is what i have to unplug and re insert to get the car to run normal.

 

 

[02Pilot]

So you mean you're physically pulling the rail with the injectors attached to it? Or you're pulling the electrical connection? I don't get how it stays running in either case, but I'm trying to understand what you are doing.

 

The only thing I see missing from the list is the AFM. The flapper-types are notorious for intermittent and false signals as they age. If that's signalling a lot more air than it's actually passing, it could be calling for too much fuel. Do you have a spare lying around to swap in for testing?

[ezlnh8u]

15 minutes ago, Andrej said:

So you mean you're physically pulling the rail with the injectors attached to it? Or you're pulling the electrical connection? I don't get how it stays running in either case, but I'm trying to understand what you are doing.

 

The only thing I see missing from the list is the AFM. The flapper-types are notorious for intermittent and false signals as they age. If that's signalling a lot more air than it's actually passing, it could be calling for too much fuel. Do you have a spare lying around to swap in for testing?

I have two spare working AFM's that i tried, and symptoms don't change. the fuel rail gives the power to the injectors. I have to hold the throttle while i unplug it. 

[ezlnh8u]

I am tempted to replace the wiring harness, I have a spare one as well... 

[jimk]

Did you just get this installation running or has it been running ok before the problem appeared?

Make sure on one in the past has installed a resistor in line with one of the wires from the temperature sensor (the one for the EFI not the engine dash gauge).  Some characters in the past thought they could get more power by making it run rich by adding a resistor there.

Also check for broken wires from the temperature sensor.  The sensor resistance is high when coolant is cold and would act similarly if the circuit was open.  One side goes to ground, the other to the engine computer.  The pinout is available for the main connector.

Edited December 4, 2018 by jimk

[Hans]

does it have an idle control valve?

[02Pilot]

So you're unplugging all the injectors and the car still runs if you hold the throttle open? If that's the case, you've got fuel leaking into the intake somewhere. Is there a cold start injector on that motor? If so, check that for leaks. If not, check the primary injectors for leaks with the rail pressurized.

[ezlnh8u]

1 hour ago, jimk said:

Did you just get this installation running or has it been running ok before the problem appeared?

Make sure on one in the past has installed a resistor in line with one of the wires from the temperature sensor (the one for the EFI not the engine dash gauge).  Some characters in the past thought they could get more power by making it run rich by adding a resistor there.

Also check for broken wires from the temperature sensor.  The sensor resistance is high when coolant is cold and would act similarly if the circuit was open.  One side goes to ground, the other to the engine computer.  The pinout is available for the main connector.

The car has had this set up for over 10 years now. engine was rebuilt 4 years ago. I will have to review some of the lines you are referring to,and see if there are any burnt signs or corrosion.

[ezlnh8u]

50 minutes ago, Hans said:

does it have an idle control valve?

Yes, I replaced it with another one from a working vehicle.

[ezlnh8u]

25 minutes ago, Andrej said:

So you're unplugging all the injectors and the car still runs if you hold the throttle open? If that's the case, you've got fuel leaking into the intake somewhere. Is there a cold start injector on that motor? If so, check that for leaks. If not, check the primary injectors for leaks with the rail pressurized.

Although the injectors were all replaced after this issue started>?

[02Pilot]

Were they replaced with known good, recently tested injectors? Old injectors are prone to dribbling fuel. The systematic way to check is to pressurize the rail, turn the car off, and watch the gauge. If fuel is leaking the pressure will drop; if not, it will hold steady indefinitely. Motors don't run without air and fuel, so again if it's running with the injectors disconnected it's getting fuel from somewhere.

 

I presume that you've checked to make sure the air filter and intake pre-throttle aren't blocked. Will the car rev at all, or does it stumble and die when you open the throttle?

 

Before replacing the whole harness, just do continuity tests on each wire that goes to the ECU. If something's grounded or shorted you should find it.

[jimk]

1 hour ago, Andrej said:

presume that you've checked to make sure the air filter and intake pre-throttle aren't blocked.

Don't believe the AFM will open if no air can get in to open the door.  Engine will run on a low load point in the map and not ad hardly any fuel.