348 Running rich, then Limp Mode

I have had a couple of cases in the past on my cars (of the 80's) when the ignition coil would work well when cold but would start misfiring when well heated up. If I switched the hot engine off, I could not restart it until I let the coil cool down somewhat. Ignition module, if on the way out, may also be ok when not too hot but start playing-up with temperature.

 

Here's one bench test you can do on your Chinese MAF:

Tape both sides of the MAF. Connect 12V supply - negative to Pin 1, positive to Pin 5 (see the diagram and picture). Measure the voltage between ground (Pin 1) and Pin 3. The spec is 1.40 volts, +/- 0.04 volts, i.e. between 1.36 and 1.44 volts. On new Bosch MAF-s, my calibrated Fluke multimeter shows values between 1.39 and 1.41 volts. Depending on its accuracy, your multimeter might show reading a bit out of the range 1.36 - 1.44 volts but it should not be much out. On some Chinese MAF-s, I have measured as high as 2.6 volts which is totally out of order.

Please note that this test covers only performance of the MAF in static (air) condition and does not verify the MAF curve. However, if the volt reading is out to start with, the whole MAF curve will certainly be out.

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Another piece of info for you regarding MAF-s: the CO screw (potentiometer) does not alter the MAF's operation in any way (does not alter the voltage signal on Pin 3) as it is not part of the MAF's electronic circuitry. It is only housed inside the MAF where one of its "legs" is connected to ground. The other leg, to which the resistance is varied when turning the screw, is internally connected only to "free" Pin 6 of the MAF (see diagram above) from where it goes to Pin 43 of the engine ECU. So, the CO screw varies resistance between the ECU Pin 43 and the ground which "trims" the ECU's fuelling curve.

 

Always after ignition failures also put in new candles. Flooding the sparks never makes them better.

 

When I was. Having some issues I installed a cheap maf but. Upon smoke testing it leaked terribly at connections so check that if installing

 

Always a good first step. Sometimes the wiring has breaks in it, too.

This powers the injectors, MAF, secondary air components, evap system components and some circuits in the ECU. It also supplies power to the fuel pump relay coil. If you're getting a lot of unburnt fuel, it sounds like this relay is ok. Same for the fuel pump relay.

 

First of all, remember that F119 is effectively 2 inline-four cylinder engines, so in this view, consider 1-4 as one engine.

If you have fuel and spark (and compression), the engine will run. If fuel or spark is off the limits, the engine will usually run, but not ok.

If you loose either fuel or spark, the engine will stop running. In this situation you can have engine firing for air or pumping excess fuel forward.

Sounds to me that when you disconnect the spark, you're shutting off the engine and starting to pump excess fuel through the engine, as the other engine (5-8) keeps running the composition. Don't do this much, as you have cats. Cats don't like to drink unburnt fuel, they are picky animals.

The spark needs to be fired exactly on correct timing, as degrees of turning of the engine. Without crank sensor signal the ECU doesn't know the position of the engine and should not be able to fire correctly.

As you have fuel, the fuel pump gets electricity and this relay is not your culprit.

As the engine runs, neither this relay is your culprit.

Unprobable for this effect IMO, but always good to keep grounds in good condition.

No. Well, the MAF might measure wrong and be the culprit. But no on the looping - closed loop is when the ECU is adjusting the fuel trims by lambda, ie. checking the output of the engine. Open loop is when the engine is driven only by the incoming parameters and not checking the output.

On open loop, ie. without the lambda signal used, to run the engine even close to properly the ECU needs to know some parameters. Basically these are the position of the engine (crank sensor), the temperature of the engine and mass of air coming in to the engine.
-By the crank sensor, ie. RPM and engine position, the ECU decides the correct time to hit the spark (and in newer engines also correct timing to inject the fuel) and use it as a parameter when deciding the amount of fuel, ie pulse width of the fuel injectors.
-By the temperature sensor the ECU knows if the engine is heating up or in driving temperature. When warming up the idle should be raised a bit and the fuel amount should be slightly bigger (warm-up enrichment)
-By far the mass of incoming air (MAF) is the primary parameter to decide the amount of fuel to put into engine. When all is good and no power is used, ie. cruising on a warm engine, the mixture of fuel and air is basically aimed at stochiometric mixture, which takes 14,7kg's of air for one kg of fuel. When warming up or WOTting the engine the mixture is taken to little bit richer, I think usually somewhere around 12:1 instead of the 14,7:1, but basically also this is quite exact game when it's done properly.

Without the MAF the MAF-driven ECU doesn't know the mass of air going into engine. Without MAF signal the ECU goes either in no-go emergency mode, which limits a lot or on an "enough" emergency mode, where it basically puts enough gas in the engine to run it surely safely by gas pedal position and RPM. Now, MO2.5 doesn't have gas pedal position sensor, so if it has this mode, it surely will be RICH.

But, after all this, I'm getting to conclusion that you have 2 possible culprits:
1) the Chinese MAF
2) FPR

..and yes, I remember that these both have probably been changed.

So, the next step for you is to take the vacuum line off from the FPR, put a hose from the FPR vacuum connector to an empty bottle and replace the fuel pump relay with a jumping wire for few seconds. If the bottle has fuel in it, your FPR is gone. Even if the bottle doesn't have fuel in it (as the FPR has been changed, I can't be sure it breaks the same way as original), I'd measure the fuel pressure.

Tl;dr: check FPR and MAF.

Edit: I might get a chance to get connected to MO2.7 diagnostics, possibly also to 2.5. Don't know yet fore sure, but I'm working on this.

 

Note the routing of the wiring...

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Yep. And the right bank doesn't know the timing at all if the signal is missing. It might be tricked if the signal is cutting or otherwise mysterious, but I think the continous sparking doesn't support that much.

It's worth to check, tough. I'm not sure if I'd change it without cheking to ensure not creating another possible problem - if you have eg. too big gap to the sensor wheel, you'll have one more fault on your hand to harden up the repair.