tylerwerrin

Hi,

i scanned my LT1 with SCAN94/95. I had a feeling the engine was running rich just from the smell and plinking in the downpipes on deceleration.

My values in both the the short term and long term trims are very high- staying at around 160, and fluctuating from there. On my scan, I noticed in articulation that bank 1 of my short term trim was pretty much pegged at 160 the whole time, where bank 2 of the short term trim seems to move around in accordance with engine RPM and acceleration and deceleration.

my question is, what should I be looking for to resolve this problem? I feel like it might be a leak at the b1 manifold to the downpipe giving the engine a false lean causing the PCM to dump fuel... but why would by LT trims both be so high if that’s the case?

Injuneer

Upload a copy of the log in .csv format and I'll download it and take a look at it.

Darrenmb

Tyler,
Is this in the jag? If so I am working on the same swap... already been through the motor, now waiting on garage to cool.down to start the swap... I may have more than a few questions for you as I proceed.

Sorry about hijacking thread... carry on!

tylerwerrin

Hey Fred!

Thanks for taking a look:

https://www.dropbox.com/s/ilpi7va335...41192.csv?dl=0

And yeah, this is for the Jag - good luck on the project, let me know if you need any help, I have a bajillion documents gathered over the past several years for all the little sub projects that come along with the conversion.

Injuneer

Downloaded, set up, and took a VERY PRELIMINARY look. Check the EVAP system hoses between the canister and the purge solenoid. The EVAP duty cycle goes into double figures (purge solenoid "open") and both O2 sensors drop into very lean range for several seconds, and the short terms start jacking up until they get the O2 sensors back where they belong. Now both the LT's and ST's are extremely high. That appears to be one problem, but it does not necessarily explain why the LT's are at 160 in a lot (most) of the cells.

Odd thing is that while most cells have the high LT"s, and idle cell (16) has both LT's at 128, and the ST's are moving over a very narrow range above and below 128. But as soon as you open the throttle, and put it into cells 01 to 15 the 140/150/160 LT"s show up immediately.

I need to spend more time on it to figure it out.

tylerwerrin

Will do - FWIW the canister is just a "generic" canister, housed in the passenger side front fender.

EDIT: It's actually a stock Camaro canister - my bad.

I checked the hoses, they looked OK visually. I'll check the solenoid itself after work.

If the evap system continues to cause problems, should I just retune & delete? I believe (although can't remember specifically) that the evap provisions are a lien item within CATS Tuner that I could just check "off"... but i'll have to check and see.

Thanks for helping out, really appreciate it.

tylerwerrin

Test the solenoid and it functions as it should... I'm wondering if there's a crack in one of the hoses and it's pulling it excess fresh air. Wouldn't that be ALOT of fresh air to cause the readings I'm getting? Fuel trim is on nearly the whole time.

Also to your point about the Idle being at 128, where it should be - if there was a leak, wouldn't that be affected too?

Injuneer

The point I was trying to make was when the purge solenoid opens, the O2 sensors go lean. That would indicate a leak in the EVAP system anywhere from the canister to the connection at the purge solenoid. I was not questioning the operation of the solenoid. It appears to be opening and closing as commanded by the PCM.

As I said, that is probably not the main source of the problem. But it is a contributor.

I need more time to look at the log. I am also working on reviewing logs for two other people currently.

Injuneer

You have two cells with no problems - 16 (idle) and 17 (decel). Those are two cells where EVAP is not used. Both of those are where the throttle % is "0".

All the others have 140+/150+/160 LTFT's. All those cells allow EVAP to operate, and it does operate throughout the log. Seems to me the problem has to trace to the EVAP system and the throttle going open. The more open the EVAP purge solenoid is (represented by "duty cycle") the more likely it is that the STFT's elevate to the 170+ range. The 160 LT x the 175 ST means the PCM is adding as much as 70% extra fuel to compensate for the low O2 readings.

Is there any evidence of spark plug fouling, rich exhaust smell, etc?

Check the routing on the EVAP system components. Make sure the upper and lower hoses that head toward the throttle body are in the correct positions: How does the EVAP canister under the hood connect to the fuel tank, and is there a pressure control valve in the system, like there is in the stock LT1 system?

http://shbox.com/1/evap_sol.jpg

http://shbox.com/1/1995_evap.jpg

http://shbox.com/1/evap_system.jpg


Something like low fuel pressure, air bypassing the MAF sensor, a large vacuum leak not related to a switched on/off component, etc. are going to be present pretty much all of the time, and would likely affect the idle and decel cells as well.

The other thing that stands out is the barometric pressure reading of 91.17 kPa. Sea level number is closer to 100 kPa. A barometer of 91.17 kPA converts to 26.92 "Hg, and that would be normal at close to almost 3,000 ft above sea level. But your location indicates Santa Monica, CA..... which is at sea level (29.95 "Hg). The low barometric pressure also shows up in the MAP sensor readings at idle, where you are getting numbers like 26 to 27 kPa.

tylerwerrin

Ha, as for the kPa, that's awesome you were able to determine where I was testing the car just from the scan file. To answer that riddle, the car is actually living in the desert, which is about 3000' above sea level. Not much space in Santa Monica for parking for a second 'fun' car when you're living in an apartment. But that's very cool you figured that out just from the reading.

The exhaust is certainly rich - I can hear the "plinking" of unburnt fuel in the exhaust too. I noticed my gas mileage was doing rather poorly the last couple tanks, so that part is probably all interrelated. I'll pull the plugs and see what they look like; I'm sure they are dark from burning all the excess fuel, so I'll have to clean them off before any other tests. They are a real pain to get at on the passenger side.

The Charcoal Canister is a stock 95 Camaro canister - I set it up like the shbox diagrams illustrate - double checked it before I went back to LA for work. Visually the hoses looked OK... maybe it's the pressure control valve on the canister itself that's causing the issue, I don't know.

I'll just cap off the EVAP nipple on the throttle body and see if my PCM BLM readings change. I believe I need to tune out the Charcoal Canister purge as well, but from what I gather that won't throw a 'limp home' code, and I should be able to do some test runs first before pulling the PCM to retune.

Thanks again for looking at the scanfile for me; really appreciate the time, effort & expertise. Let me know if there's any way I can repay you down the line.

I'll update the thread once I get back out to the desert to drive the car in a couple weeks to see if there is any improvement.

Injuneer

Capping the EVAP nipple on the TB is the best way to go. See what happens.

There may be something else... but we'll see.

The barometer thing was just to verify you were actually operating the car at that elevation. Otherwise, we could have been looking at some sort of MAP sensor problem.

tylerwerrin

So I pulled off the EVAP hose and capped the nipple on the throttle body. I ran the car and was getting very weird fuel trim readings - above 160 in many cases for the ST readings (up to 200+) and remaining at 160 for the LTs. The engine seemed more sluggish than it had been previously, before I had capped the nipple.

https://www.dropbox.com/s/v8ayw0g2p2...02019.csv?dl=0

I noticed, going through the scan that I was spiking in BLM cell 10 & 11, during full EVAP duty cycle. The evap purge solenoid is still connected to the harness - should I try disconnecting the evap solenoid so the PCM will not be getting any readings whatsoever?

Any ideas of what to try next?

Injuneer

Unplugging the EVAP purge solenoid should set DTC 26. According to the manual, when DTC 26 sets, the PCM disables the driver for the solenoid, to prevent PCM damage. Logically, with no purge being commanded, the PCM should not make any of the adjustments it normally makes when the EVAP system flows. But that's just an assumption. "Limp mode" has nothing to do with the PCM seeing a few codes. That is only used when the PCM has virtually no input at all.

Keep the vacuum cap on the TB nipple.

And you checked the positions pf the hoses on the solenoid, and on the TB?

tylerwerrin

Alright, I'll take it out for a drive with the EVAP solenoid unplugged to see if that makes any difference with the weird/extreme readings I have been getting.

The nipple just below the EVAP nipple on the Throttle body is capped as well.

tylerwerrin

So, just as predicted, when I turned the car on, it tripped code DTC 26 after about 10 seconds. The fans kicked on and the Check Engine light went on. I didn't drive it at this point because I wasn't sure if limp-home mode was engaged or not, so I shut it down and removed the code with Scan9495. I've never driven around when I have a code, so just wanted to be safe and confirm here that it's OK to drive with the fans on and check engine light on for DTC 26.

If I had my bench harness & tuning laptop with me I'd just program it out with TunerCATS... but alas, it's not here.

Thanks as always...