My '94 sarted bogging on me the other day. At first I thought it may have been a tuning issue, but it doesn't seem the case. The car has been runing fine on this tune for a long time now, and autocrossed just fine a few weeks ago.

The bog started at low load around 2-3000rpm in third or fourth gear driving around town. The engine 'misses' or 'bogs' momentarily, followed by a 11-12 AFR readout on the wideband. It sometimes continues to bog with the rich conditions, and other times it levels back to cruise AFRs (14-15). On the highway this morning, it seemed to be a little worse than the last few days.

I'm planning to change the plugs and wires before driving again. It probably will not hurt to recalibrate the widebands also. Anything else I should be worried about?

 

The only way to get a rich reading on a WBO2 is to be rich. Any other problem (misfire, etc.) results in a lean reading because there is excess O2. If you go rich beyond bog all the way to misfire, that will read lean too.

So, what's up with fuel pressure? What's your setup? Do you have a big fuel pump overpowering the FPR? Stock FPR? Bandaids?

 

The car is naturally aspirated with MSPNP1, innovate LC1, walpro 190lph, stock fpr, ev14 550cc injectors. 145k miles or so on the engine and chassis.

 

If you have MS, you should be able to log the events. That would help.

Those are darn big injectors and a lot of fuel pump for a naturally aspirated car, BTW.

 

Yeah. The car was boosted the past two years, and I wanted to step down to the non-boosted street class for autocross this year. I will try to log it later today. I agree, we should be able to see the anomoly on a log before the rich condition that I see on the local gauge, right?

 

I would think so. Ultimately, it's the MS that's deciding on the PW of the injectors. It would be nice to see what it is responding to. This assumes, of course, that the FPR isn't being overwhelmed or we aren't asking for such a small PW that the injectors can't really deliver. Given how much history you have with the setup, the above seems unlikely -- although it would be easier to control smaller injectors.

 

Ok. I logged my drives today. Below is a snippet from where it occurs.

I see that Gego goes to 100% at every instance I get the rich spike and bog. I presume this would be linked to a failing wideband sensor?

 

Would have helped to have posted the log file.

Gego of 100% just means that the MS has transitioned to open loop for some reason. 100% means that the exhaust gas feedback gain is 1 (i.e., no gain -- Gego is not making any adjustment to the injector pulse width). That doesn't necessarily mean that the VE table is being used directly, as there are other gains.

In general, when operating in closed loop, it looks like your Gego is trending towards 90%. This is probably the limit of the authority (10%) that you've granted it in the "Exhaust Gas Settings" dialogue.

Bottom line, your basic tune is too rich. If you've got a good VE table, you should see Gego trending above and below 100%, hopefully less than 5%. Time to go do some fuel tuning to get your VE tables squared away. I'd start with a free air calibration and then head out to either autotune or log and use VE Analyzer.

 

I'll post some more tonight. The log is around 7mb, but I'll see if I can get it up.

With what you've said, I am already replacing plugs and wires since they are about at the point they could be replaced. I'll free air calibrate and see if I'm being overly agressive on any other gains. IIRC I last touched the tune before putting it away for the winter, and the clt/air-temp correction may need adjusting for hot weather.

 

??? Not sure what you're referring to.

 

Coolant Related Air Density is what I was referring to.

You were quite helpful. Thank you.

The solution was the combination of recalibrating the LC-1 wideband, removing 1 point in the Fuel VE Table at lower rpm, 2 points in the higher rpms, and reducing the correction on the hotter end of the coolant related air density table.

Looking back to the end of last year, I probably tweaked the tables a little bit when it was cold and the issue only showed up now that spring/summer is here.

I took the car out for a spin around town, and the ego correction stays within 3-5% now.

 

Are you actually manually changing your VE values?!?

You should be using Tunerstudio's Autotune or MegaLogViewer's VE Analyzer function. That will give you far better results. I'm an "old school" VE Analyzer type myself.

 

Manually fixed what I needed to.

 

There is also air temp enrichment that depends on the temp the air temp sensor sees.

 

Thanks for your help. I bit the bullet and retuned the entire fuel table on my way to work this morning (~20mile highway drive). I turned off: overrun, accel, ego and clt related air density and also recalibrated my TPS open and closed limits.

For the ride home, I turned everything back on, one by one, and think I found the culprit. The AE Driven Fuel PCT goes nuts at partial throttle. I shut off Accel Enrichments and the car drives perfect. Time to troubleshoot the TPS sensor.