-nick

Hi folks,
This should be an interesting one. I ran the 1991 C4 on a dyno a couple years ago and to do a before/after swap with the Steve Wong chip. The afr was very rich on the stock chip and Steve's chip. I thought at the time that the shop's tailpipe wideband o2 may not be too accurate.

Recently, I installed an Innovate wideband o2 on place of the stock sensor. I'm using the simulated narrowband to feed to the motronic. Everything is working the same as it always has. But now I've confirmed the dyno shop's tailpipe numbers. I'm getting exactly the same afr on a 3rd gear pull from 2k-redline.

So what the heck is going on?

The motor: stock exhaust, stock everything except a change to Dougherty's 993SS profile cams when I did the top end this year, and the Wong chip a few years ago. Honestly, I don't really notice much of a difference from them. Definitely no differences related to the issues in this post. New caps/rotors/plugs. New CHT. Output from scantool looks pretty normal. Have done an idle adaptation. Recent top-end didn't change any of the behavior. Injectors have been cleaned/flow balanced in the past. Charging volts are good. ISV cleaned ~4 years ago.

Symptom only shows up at WOT. Cruise and idle AFR's are steady at 14.7.

I checked the fuel pressure at the fuel rail access port, and vacuum by tee-ing into the fuel pressure regulator line:
idle rpm, ~980, 50psi fuel, 15"hg vacuum (a little low due to the sport cams?)
2000rpm, 48psi fuel, 21"hg vacuum
3000rpm, 46psi fuel, 22"hg vacuum
4000rpm, 46psi fuel, 22"hg vacuum

Fuel pressure without vacuum is 55psi (3.8bar).
Vacuum at idle with idle switch open= 1"hg higher, 16"hg on the gauge.

Compression quickie only ~1,000 miles after new rings, left bank only, throttle shut (duh moment), engine slightly warm, lots of cranks on each:
184 psi #1
178 psi #2
185 psi #3

A few, possibly related, symptoms to the odd fuel injection behavior:
1. cold (<30F) starts always give me a hunting idle for a minute. Watching the wideband, the afr tends to hang out above 14.7 (stoic) more than it hangs out below. Although it oscillates between ~14.5-15.0. It will stall
2. Restarting from hot, after sitting for ~5minutes, I'll sometimes get a start/stall. If I give it some accel pedal, then it will stay running, but if I let off the pedal before it calms down, it will stall.

Can you think of anything left to check?

ps- Please keep any non sequitur chip-bashing comments out of this thread. Thanks

-nick

<crickets>

Any ideas at all? Why would WOT, open-loop map, run so rich?

Rocket Rob

Sorry I can't help. Have you tried contacting Steve Wong? Is there something amiss or needs to be corrected with the DME chip?

Edit: One other thought, are your injectors originals or have they been replaced some time in the past? Could they be flowing more than expected?

JasonAndreas

To cool the cylinders when the engine is under load?

BHCfarkas

I don't see anything out of the ordinary at all...

Most cars are tuned to be around 11-12AFR around full load or WOT and as mentioned it's to support fueling demands as well as promotes a "cooling" effect on the cylinders. I'm not sure what it is you're worried about exactly, so maybe you can explain better.

Jjm4life

Seems normal to me. Seems too practically never dip below 11.5. Fwiw, I have used innovate wide bands before. They are very accurate as long as the initial setup is spot on. From memory, it was fairly tempermental until I got it right.

-nick

Rob- Good thought on injectors. I'll see if I can read a number from them without having to pull one out. If the slightly bigger 993 injectors were installed at some point, that could be enough to go rich on open loop but still stay within the target during closed loop.

All- This isn't a turbo What stock n/a cars are you seeing 11-12 afr's? 12.5-13.5 is the usual target for wot power. On the richer end for max torque, and leaning out slightly afterward.

Thanks for sending some feedback!

BHCfarkas

Typically higher compression cars run 11-12AFR.. but I'm no expert, so maybe someone else can confirm.

My experience is based on the various high-compression Toyotas I've built in the past. Usually 12:1 or 13:1 compression with 45DCOE weber side drafts. Tuning those you're looking at very low 11s to prevent detonation and etc.. But that also has a part played by how well certain injectors and fueling methods atomize.

-nick

Bummer, injectors check out. pn 0 280 150 731. That would have been a nice solution.

Confirmed with Steve Wong that something is going on. He targets 13.0-13.2 at wot.

Only thing left on his suggestions list is afm spring tension. Anybody have an extra afm to loan out for a quick test?

Duck

I have one you could borrow, but would have to ship from NC.

-nick

pm coming!

-nick

Many thanks to Duck for loaning me a spare afm! Sadly, it just confirms that mine is perfectly fine. Still hunting for the culprit.

This is what I got from testing the AFM output voltages:
My AFM: closed= 0.26V, open=4.49V
Duck's AFM: closed= 0.26V, open=4.42V
Manual says: closed=0.25-0.26, open=4.6. “Approximately”.
Both are a little low, input voltage is ~4.96V. Nothing too out of line.

I finally got obdplot running, though I had to pull the numbers out of the log file and plot them up myself. Very coarse 1 second resolution from obdplot. I'll look at the source code and see if the sampling time can be improved. I lined up the afr values out of the innovate log file. I left out ignition advance. Not sure if Steve Wong wants his curve advertised, however, it looks perfectly reasonable. Good thing most of my career is spent making figures!

New request: does anyone have an obdplot logfile with a wot run in it? I want to compare injector pulse widths.

alexjc4

Can you check the amount of trim that it is using to hit 14.7 in closed loop? If there's lots of trim needed in either direction that my guide you a bit.

Also can you verify the knock sensor operation? It may be reading false knock and running rich and retarded on wot.

-nick

Alex, good thoughts. I'll check the trim numbers.

Advance is hovering around 24 degrees for most of the range, then increasing to about 26 at very high rpm. Timing doesn't appear to be getting pulled.

I made a run with the idle/wot sensors disconnected. Limp home wot mode is *extremely* rich! Hanging out in the low 11's throughout the rpm range and I could smell the exhaust stench after coming off the throttle. At least I know that I'm not stuck in this mode.

I also checked afr after plugging the intake port to the fuel evaporator. No change there. There is another one ruled out.

I'm tempted to just burn a leaner wot chip map until I figure this out.

jstyer

That just doesn't seem very rich to me... 11-12 is a totally normal value for WOT, perhaps just a tad conservative. You're asking for problems trying to chase down 14+ in wide open running.