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Thanks. I’m wondering about the throttle body, idle control, and EGR.

OK, had another look at this today. Started engine with the MAP sensor connected. Gave it some revs to keep it going. I was about to get an old vacuum gauge to aid diagnostics but thought to look at MAP readings again first.

I'm confident the MAP sensor is reporting the correct readings at idle (checked against barometric) and idle. After a cold start it went to fast idle at 1122rpm and MAP reported 746mBar which is 22in Hg. I know the engine should be warmed up but I think that is close enough. Engine load around this idle speed was reported at 55-60%. This seems to be high? Again there is a high negative fuel correction which seems to relate to this calculated load.

A couple of minutes in I got the following rpm/load figures:

1500 / 40
2884 / 22.3
794 / 72.1

Another minute running:

3137 / 20.5
847 / 65.8

And just before she stalled:

2337 / 31.5
419 /68.9

As the engine started to falter I switched to check Bank 1 Lambda Control (Group 33). The correction was going from -50 to 60% at idle speeds down to approx -30% at 2000 rpm plus. The Bank 1 sensor voltages were around 0.4x volts over the above engine speeds and corrections. Some sample data below.

TIME Lambda Control of Oxygen Sensors
STAMP % V
1.01 -50 0.44
2.54 -53 0.434
4.11 -48 0.43
5.64 -55 0.506
7.19 -21 0.468
8.7 -14 0.474
10.25 0 0.464
11.78 -17 0.432
13.31 -30 0.444
14.84 -40 0.44

Those appear to be significant corrections. Do the sensor voltages correlate with them? I thought O2 voltages transition between 0.1 and 0.9V for lean (add fuel) and rich (reduce fuel) respectively? I was expecting a wider voltage range against corrections.

It seems to be overfuelling based on a high calculated load then adding corrections to counter it? Again, when it starts to get warm the engine falters and stalls. I probably could keep it going with a bootfull of revs (upper 2000 rpm). I think it's on a different fuel map at some point when the revs go up (calculated load drops).

When I stripped the old engine, I left the fuel rail connected and just put it to one side. I fitted new lower seals to the injectors and did not remove them from the rail to do the upper seals. There appear to be only one fuel pipe from the tank and then the evap. Is there any possibility I've caused any problems in this area? Is the calculated load higher than it should be? What might cause that? I cannot imagine these symptoms can be caused by the EGR.

Only questions I can think of at this stage.

Are you 100% you dont have a vacuum leak anywhere?

I am not 100% certain but I cannot find it. That was one of the reasons I was thinking to connect a manual vacuum gauge. One thing I could do is disconnect all vacuum hoses and plug them on the intake side. I could also take off the throttle (again) and inlet manifold and check the gaskets (intake seals (rubber) are new, throttle body (metallic) is reused). If the weather is fine tomorrow I'll do a more thorough propane test before stripping down to check.

I mentioned earlier how the throttle body/butterfly was hissing when I ran with the MAP sensor unplugged. I did notice today that with the MAP sensor plugged in that hissing seemed to be a lot quieter. I guess this is due to a different butterfly position/fuel-air mixture.

The hissing is just due to the air passing over the butterfly. Its quite normal (you wouldnt hear it if the air filter was attached)

Yours doesnt have a MAF sensor does it?

No MAF, only MAP.

Thats what I thought

Its strange, its almost like it thinks (or is) running very rich, then making excessive adjustments, thus starving the engine of fuel due to it being leaned out too far.

Is it worthwhile blanking the EGR at the throttle body to see if it makes any difference?

You could try, but normally, the EGR will only operate when the engine is at full temperature.

It is strange. It seems that it is likely bad data or a miscalculation.

If I understood correctly load is calculated mainly via MAP, engine temp, throttle position. I've changed the former sensors, which leaves the throttle. I'll check again for vacuum leaks and at again at higher rpm to get more data and see if it runs OK. If that all looks good it might be idle related (but I have not a clue how that would indicate a such high load).

Have you got a spare TB to test with?

No, I only have the original.

I've done several TBA's with the original TB. Might give that one more try after I've run the engine up to temp.

What makes no sense is it was all working before you switched the bits around. I almost feel we need to take a step back and look at physical things, like gaskets, compression, hose condition, vacuum leaks etc

That is what I was thinking this morning and that a vacuum gauge tester would help to highlight the problem area. It might be worthwhile to do that.

I've ordered a vacuum tester/gauge to help with diagnostics.

Did another TBA after disconnecting the battery for half an hour. No change. Blanked off the EGR but no change. Engine ran quite well at idle from cold up to around 40C before faltering (MAP sensor connected). At least that much is consistent.

I checked the inlet manifold and brake vacuum pipes and all looked OK. There is a corrugated pipe from the oil separator up to the inlet manifold. Not sure how this is supposed to seal - is there an O ring? It seems to be a bit loose (small lateral movement and easy to rotate). Does the oil separator open up that airway all the time when the engine is running or only at certain times? I'll check the oil again after it settles down as I think it is using some, although there is no smoke at all from the exhaust and the plugs seem to be sooty from a rich cold start fuel mixture.

Only other observation I had is the exhaust note at the tailpipe sounded a little tinny and the exhaust gas was not pulsating strongly (although it was off cold start by the time I checked). Can't say I noticed it before so cannot make a comparison.

Will wait for the vacuum gauge and report back on readings.