RPM'S dropping when peddel steady....

**Rally Smith** · 07-23-2012

On Saturday I was driving thru town and my 95 GMC K1500 TBI started hesitating and even died when I was coming to a stop. I got a SES light and hooked my computer up to it. Computer said, O2 Rich. I checked the file I was running the truck on with the one in my computer that it should have been. It failed the 3x I checked. So I updated the autoprom with my current bin. Everything seemed fine Sunday and this morning.

On my way back from lunch it began again. Even in Park I just brought the RPM's up to 2500 and held it steady and the RPM's were dropping 400 to 500 RPM's and would recover and would repeat. This is a brand new OEM replacement engine. I replaced all of the vac lines & sensors except for the MAP sensor. I'm running the LM-1 wide band O2 sensor with the narrow band signal coming from the LM-1 to the factory O2 harness to fool it. I have been driving this engine for the last month or so with no issues.
Not sure on how to proceed from here, any help would be appreciated.

I should mention that I had a hesitation problem (idle) with my last engine and this one is doing it as well. PITA! But this is not what I'm referring to, just thought you should have all the info.

Thanks,

Rick

**EagleMark** · 07-23-2012

I've never had a simulated O2 sensor signal work, at all, to run an engine. But then never tried on a stock type engine. Even after tuning a built engine I tried and it sucked! Others say ah, OK but still not as good as real O2 reading. The simulated O2 is not a real reading so BLM learn never learns. Before you go nuts try the stock O2 sensor...

The hesitation on 2 engines leaves the parts that were shared. Having injectors serviced, TBI rebuild and checking fuel pressure will probably fix that issue, starting with fuel pressure. If it's not 13 PSI it's not right. OK with all the cheap gauges at least 12, yes they will run to 9, but not optimal at all! You would have noticed your wideband going lean at WOT if it were dropping, does not mean it's enough at idle...

AutoProm has given me similar issues and I have learned to always Verify the Uploaded Bin. Even though it says Upload successful, when Verified it fails! Then Upload and verify again and it's good. I know you've used this before, but will add for others Mask ID has to be set to AA to disable Checksum for emulating.

Other ideas?

**gregs78cam** · 07-24-2012

Sounds like the exact problem I had with my LM-1 Sim O2. When it would go Closed Loop, I would get lean spikes and hesitation. My suggestion is definitely put in a NBO2.

**Rally Smith** · 07-24-2012

O.k. let's forget about the slight hesitation for now please, the truck has done that since I bought it a few years ago. My main concern is the dropping of RPM's and stalling out.
Mark, I'm running 15 psi, the injectors were serviced less than a year ago and the T.B. has been serviced. The truck has true dual exhaust w/ headers, TBI Spacer, K&N air cleaner with the Hypertech Power Charger. (http://marine-performance-parts.com/...gmtbi5057.aspx).

I do not have my computer hooked up all the time when I'm driving around. My Auto Prom is plugged in in place of the chip. I'm running off of it.

I'm confused, if tuning with the Wide Band is supposed to be the way to go, then why would I want to plug my NBO2 sensor back in?
Am I better off just disconnecting the LC-1 and tuning the engine that way?

**EagleMark** · 07-24-2012

Well the narrow band simulater is not giving the actaul O2 sensor reading, so your BLM data is wrong. Your BLM data is simulated data. So to tune fuel you need to rely on WB only and even that is skewed by a simulated NB signal to ECM adjusting fuel. I really have not found the purpose for it other then messing up good data for tuning?

I found using NB BLM data or tuning open loop with Wide Band much easier and accurate.

Your right, if you had injectors serviced and running 15 PSI hesitation should not be an issue, rich bog possibly? But putting that aside and dealing with the issue your having still has 2 guys saying the same thing. Stop using the simulated NB and see what happens either Closed Loop with Narrow Band O2 sensor or Open Loop with Wide Band.

The engine is tame so I like NB tuning it since that's the way it will run in end, then Wide Band for WOT. 14.3 Stoich is more accurate for todays 10% ethanol enhanced (ruined by adding food/corn) fuel.

Then if it still dropping RPM and stalling we can look for an issue.

**Rally Smith** · 07-24-2012

So from what I understand Mark, I'm going to disconnect the LC-1 and reconnect my NBO2 and tune it like that....? I know I need to adjust the PE throttle position % to stay out of it while tuning. Do I need to adjust anything else while doing this? FYI, the EGR is Disabled already. How do I know what the correct O2 reading is with the NBO2?
I'm just concerned with Closed Loop at this time.

Thanks,

**EagleMark** · 07-24-2012

You got it, now if you had another O2 bung you could leave the Wide Band as well. But Wide Band O2 sensor needs to be 3-4 feet back from exhaust manifold, Narrow Band is mounted much closer if you look at most factory stock positions. Stock position is to close for a WB sensor and can damage it, less likely with mild engine...

Don't worry about NB O2 readings, it's a differant animal and will not give you anything to work with other then BLM history table to adjust VE off of. Do you have Dave W VE spreadsheet?

**Rally Smith** · 07-24-2012

I think I have that spread sheet.... I am familiar on adjusting the VE Table to adjust BLM #'s to get close to 128. My O2 bung is just after the header collector connection. Is that too far for the NB?

I don't want to get too far ahead of myself right now. Hopefully that change will fix my aforementioned problem. IF that takes care of it then I can continue to get the BLM's where they need to be. After that then I will move onto........?
I'll drive the truck for the next few days with the change and report back with the results.

Thanks again fellas,

Rick

**EagleMark** · 07-24-2012

that is a good spot for wideband O2, little far for unheated NB O2 but it does work, may go OL at idle or on highway in winter.

**Rally Smith** · 07-26-2012

It's in the factory location.....
Also, the sensor is a 3 wire.

**EagleMark** · 07-26-2012

How can the O2 sensor be in factory location and after header collector? Anyway with heated O2 you should not have issues staying Closed Loop.

**Rally Smith** · 07-27-2012

Originally Posted by EagleMark

How can the O2 sensor be in factory location and after header collector?

That was the location of the O2 bung in the factory exhaust system. I just had the bung put back in the same spot when upgrading to duals.

So far so good with no problems with RPM'S dropping with the change to the narrow band O2. I'll begin data logging this weekend a bit.
Do I need to adjust the PWB or anything before I begin?

Thanks in advance.