Suddenly pig rich

[Jim Blackwood]

So there I was, happily tuning along, in pursuit of the ideal PID settings for my IAC in order to get a good smooth idle and making actual progress, when after a rather minor amendment when I loaded the tune and restarted, the engine had lost it's mind.

All sense of reason completely thrown out the window, it began behaving like it had buckets for injectors and very quickly would not start at all.

Why would it do this to me? Anybody have the remotest clue what single failure could cause it? 'Cause I'm all ears.

I blamed the ignition switch and went on a 2 month long campaign which eventually got me right back to the same point of failure. Naturally I first tried earlier and earlier backups all to no avail. I've forgotten which all of the parameters I checked when it first happened, and so I'm starting back over with injector size, but I don't think that's it since I tried 3 different controllers with 2 different OS's and half a dozen or more different tunes, all with the same result.

It has to be a failure in the vehicle wiring or sensors, right? But why rich?

Your suggestions most gratefully received,

Jim

'411 P-01

[kur4o]

I will suspect some mechanical failure of injector or fuel pressure. Leaking injector can lead to pig rich fast. Higher than expected fuel pressure can also make it pig rich if you have oversized injectors. The injector failure can be intermitten, making it really hard to pick.

[brian617]

Look at Temp and BARO pids, make sure they aren't crazy numbers.

Biggest influences of mass fuel pulse width change

[Jim Blackwood]

Thanks. I think I'll try to run a datalog tomorrow and see how it looks. I've been thinking about what kind of failure would do this and it seems like the most likely suspect could be the MAP sensor if it's possible for a failure to look like full pressure. With a 2 bar sensor that should be able to cause a massively rich condition. But first I should probably look at the injector times. That should show something is up. Or at least divide the troubleshooting between mechanical and electrical.

Jim

[Jim Blackwood]

I think the datalog is going to be usable but the extension is not an acceptable file type here. I seem to recall there was a way to still post it but I forget, something about changing the extension I think. Wish we could fix that.

So I took a screen shot. But of course I can't just paste that here. Something else I wish we could fix. Pasted and saved it in Paint. I think that will have to do.

Now, I'm not positive that My scanner is set up right but there are some things about this MAP trace that certainly are NOT right. Like an average kPa of 200 when cranking. Note the engine fired off only after I had unplugged the fuel pump relay. Then the MAP pulled down as far as 53 before heading back up to 131 after the engine had stopped. So why didn't it at least drop to 131 while I was pulling the fuel pump relay? The engine was not cranking then.

Now to start with, since it is a 2 bar MAP sensor the range of 0-210 should be correct. However, MAP at cranking speed should be around 90, not twice that. So it sounds like something in the MAP parameters are not right. This confuses me further since it had been working correctly to all appearances. I do not see a clear way that a wiring or sensor failure could cause these errors. I wonder what would happen if I just unplugged the MAP sensor?

Jim

OK that seems to confirm the MAP as the problem area, with the sensor unplugged the engine fires right up but then dies. However it sounds like it might continue to run if it was warm. So, it looks like I need to sort out why the MAP has those readings... not really sure about that one. I played with MAP settings early on when I was trying to find a way to deal with the blower but haven't looked at it since I loaded the 2bar OS. Apparently something there isn't quite right. Back to my studies I guess but at least I have some idea of where to concentrate.

[brian617]

Look at MAP key on engine off and compare it to BARO. Hard to read values in screen shot in respect to cursor placement.

[Jim Blackwood]

That's part of the oddness. Baro should be somewhere around 99 at 600ft above sea level where I am, though I don't know where to look for that reading (any suggestion?) KOEO the MAP reads zero until the engine begins cranking and then jumps to 197.8 kPa and holds there until the engine fires off, at which point it drops as the RPMs come up, hitting 53kPa or about 13.6 in.Hg on that trace. Considering the throttle was very slightly cracked and the IAC may have been open some as well that could be pretty close to real values for about 2500 rpm. This is taking all readings from the "Manifold Absolute Pressure - 2 bar" PID (channel) in VCM scanner. So the running values seem in the ballpark but the cranking value is whacked. And then the value after it died (ran out of gas because the FP relay was pulled) came up to 131 kPa which again is whacked.

I went back through the receipts and swapped sensors, apparently I was sent a 2 bar instead of a 1 bar (no P/N or visible external difference). Doesn't explain why it worked and then it didn't but now it's at least starting and showing a lower MAP reading. Still not right but it looks like I may have a usable sensor now. With the right part number I'd willingly buy the one that gives the ideal output.

This sensor is either P/N: 12615136 (Camaro) or 16235939 (GMC). There could be pin connection differences. I'm wired for Signal on B, +5v on C, and ground on A. Photo below. Pin A is on the left of the connector with the wires up and facing the latch.

After swapping the sensor the engine starts easily and then dies. (I'll work on that once the MAP is sorted out) Map reading is roughly inverse to RPM however initial KOEO gives a zero reading. After the first start/die cycle the MAP reads a steady 65.8 kPa which I'm sure can't be right as I'm at 600 ft above sea level. That comes out to slightly less than 10 in of vacuum which is ludicrous with the engine stopped. It dropped to between 22.2 and 26.8 on the three start cycles I ran, or around 21-22 in, of vacuum, a reasonably good number. probably within range if the at-rest reading was 99.

So what I'm seeing here is that it looks as if the OS is calibrated for a MAP sensor that is not the one I am using. Do you guys concur?

Jim