Brain-trust help on weird AFR's

[mark houghton]

Been having this weird thing since last summer, and still present with the first ride this year. Here are the symptoms: AFR's are good-to-go, just where I want them at steady cruise (high 13's to low 14's) and properly rich at boost. Relatively steady throughout rpm ranges when not boosting.

But...what I've found...is that after an extended run and only after shutting down for a few minutes (like stopping to stretch, or going in to buy a beverage of my liking), upon restarting everything is cool AFR-wise until when rolling I hit around 3200 rpms and the AFR's drop to 12.0 almost like a switch was thrown. Bring the rpm's back below 3000 and AFR's go back to normal. No noticeable difference in the car's performance, just suddenly going way rich. Shut down, let the car fully cool off (like hours later or tomorrow) and all is well.

I initially thought that I've got a plug that's fouling or misfiring enough to cause poor ignition in that cylinder (said plug showing up only after the car sits off for a few minutes?, but I'm not sure if that logic holds water. Poor or non-existant ignition means the gas hasn't burned completely resulting in all the oxygen not being fully consumed. The wideband O2 sensor should pick that up as a lean condition...since that's what the sensor does, measuring O2 content in the exhaust. The same should hold true with poorly atomized fuel from a bad injector...incomplete combustion = O2 left over = lean reading on the wideband.

Would be nice if I had on-board fuel pressure monitoring to see if my control pressures are doing the funky chicken. For kicks, I did sit in the driveway idling at about 13.6 AFR (a bit low after a long run) and pulled each pump relay. Pulling the forward-most relay (front pump?) had no effect on AFR's but did cause the rear pump to strain (made more noise). Pulling the rear pump relay caused a drop in rpms and the AFR's to go way lean.

Any ideas?

[smurfbus]

WUR and AAV heater elements get their power from the rear fuel pump relay too so it might think its on cold start if the rear relay is bad.

[mark houghton]

Originally Posted by smurfbus

WUR and AAV heater elements get their power from the rear fuel pump relay too so it might think its on cold start if the rear relay is bad.

Yep, but the rear relay is good (it's new, and unplugging it causes the rear pump to quit as it should - so I don't feel it's the culprit). If that were the case (loss of power to the WUR) then I would expect the rich condition to be there at all times... not just when reaching 3000 rpms, then returning back to normal below 3000.
I may just have an IC o'ring or a vacuum line going bad that doesn't exhibit any problems until it gets heat soaked with the engine off for a few minutes. I don't know....but thanks for your ideas.

[speednut]

I had a similar problem , thought maybe the CP was acting up and I strapped a pressure gauge the my 3rd brake light so I could see it in the rear view mirror , it helped me to narrow down my issue.

[PrimeMvr]

Vapor lock causing low CP that can't control the plunger as SP rises?

How's that for ironic Mark, ME trying to help YOU. I read a Bosch manual and think I'm an expert now, LOL.

speednut: Love the "strap a gauge to the brake light" method!

[WERK I]

Mark,
Try disconnecting the Thermo-time switch connector at the left cam cover housing. Tape it up to prevent it from accidentally touching ground. I believe the switch opens once at warmed up.
This should rule out the bimetallic strip in the WUR causing the differing AFR's........maybe.

[Cameron62]

Please pardon my lack of knowledge. I'm learning.

What is AFV and how is it measured. What does that measurement refer to?
What is the WUR?
What is the CP?

[mooney265]

Originally Posted by Cameron62

Please pardon my lack of knowledge. I'm learning.

What is AFV and how is it measured. What does that measurement refer to?
What is the WUR?
What is the CP?

You mean AFR, right -- Air to Fuel Ratio - 14.7 is ideal for cruise. Lower is more Rich and Higher is more Lean.
WUR: Warm Up Regulator uses SP [system pressure] to create CP [control pressure]
CP: Control Pressure - the downward pressure on the FD [fuel distributer] plunger. The more pressure, the leaner the AFR and vice versa...

[mark houghton]

Originally Posted by WERK I

Mark,
Try disconnecting the Thermo-time switch connector at the left cam cover housing. Tape it up to prevent it from accidentally touching ground. I believe the switch opens once at warmed up.
This should rule out the bimetallic strip in the WUR causing the differing AFR's........maybe.

That's worth a shot, can't hurt to try it out. Maybe that nasty little bugger is malfunctioning when she gets heat soaked or something, going into a cold start injector mode. Weird, 'cause the thermotime switch - going by it's namesake - should only be energized for just a few seconds on a cold start until its heating element and/or time shut it down.
But again, one would think that would cause rich-piggies throughout the entire rpm range. I'll unplug the dude next time I'm out for a spin.

Keep the thoughts coming!

[mark houghton]

Originally Posted by Cameron62

Please pardon my lack of knowledge. I'm learning.

What is AFV and how is it measured. What does that measurement refer to?
What is the WUR?
What is the CP?

Cam - my man - being new to the game, what you need is a list of acronyms. Go here:
930 Acronym help

[mooney265]

Mark, if you can mimick the problem in the driveway - - say, restart when warm and get the RPM's to the point where you see the richness - - THEN, have a helper keep the RPM's up there while you climb below car with infrared tmeter and shoot each one of the header ports.

Make a note of each of the temps. maybe, you'll see on cylinder running rich [by the lower temp reading...]. Then, you could take it from there...

[mooney265]

Originally Posted by mark houghton

Cam - my man - being new to the game, what you need is a list of acronyms. Go here:
930 Acronym help

Thanks Mark, forgot that was out there...

[mark houghton]

Originally Posted by mooney265

Mark, if you can mimick the problem in the driveway - - say, restart when warm and get the RPM's to the point where you see the richness - - THEN, have a helper keep the RPM's up there while you climb below car with infrared tmeter and shoot each one of the header ports.

Make a note of each of the temps. maybe, you'll see on cylinder running rich [by the lower temp reading...]. Then, you could take it from there...

Good suggestion, I was actually thinking of doing that the other day. I think I can get my hands on an IR temp meter at work (we use them for routine PM's on electrical panels, looking at the huge amp drawing buckets for hot spots). No doubt, I need emperical data to point me toward a cause...then, I can work on a solution.

[Cameron62]

Mark & Mooney265, thanks much.

One last question and then I'll quit trying to hijack this thread.

How do you measure AFR?

[smurfbus]

What if your enrichment delay is acting up and you have enough boost for the bl wur to start enrichen?

Couple of scenarios: WUR stops getting power or as mentioned earlier the cold start injector starts getting power. I don't know if a injector can fail in a such way that it momentarily shoots wide open and then works again when rpms drop?

[infraredcalvin]

Originally Posted by Cameron62

Mark & Mooney265, thanks much.

One last question and then I'll quit trying to hijack this thread.

How do you measure AFR?

Dick, where are you, he's begging for your setup...

Sorry, couldn't resist, you measure Afr with a wideband o2 sensor. Look up innovate motorsports LM2. There are others as well, I have this and it does what I want and more, not the easiest to set up though.

[smurfbus]

And not the best for quality either. I would get the innovate LC-1 and a gauge for starters.

[mark houghton]

Originally Posted by smurfbus

What if your enrichment delay is acting up and you have enough boost for the bl wur to start enrichen?

Couple of scenarios: WUR stops getting power or as mentioned earlier the cold start injector starts getting power. I don't know if a injector can fail in a such way that it momentarily shoots wide open and then works again when rpms drop?

Possible, crossed my mind as well. But (sorry, I'm full of buts) I also have in-line an rpm activated solenoid to prevent any boost signal getting to the WUR until much more than 3000 rpms. But that doesn't mean that the WUR itself isn't for some reason allowing boost enrichment when it shouldn't be (or perhaps my solenoid is stuck open). It's the fact that all this seems tied to rpms that doubles the mystery.

I may have to try Speednut's idea of strapping my CP test gauge to the third brake light so I can actively watch pressures on the fly....if the lines are long enough.

I do have a digital WUR on the shelf but am reluctant to set it up until I know just exactly what is going on here.

[mooney265]

Originally Posted by smurfbus

Couple of scenarios: WUR stops getting power

I like that suggestion... You should switch the AAR and WUR plug because they're on the same loop [assuming you still have that AAR plug in the engine bay.

You could have a slight short in the plug, causing your WUR to go in and out of warmup mode...

[RarlyL8]

My stab at an internet diagnosis is the electrical connection is weak due to age OR the WUR needs rebuilt as the bimetalic strip is flaking out and loosing linearity.