LT1 Based Engine Tech 1993-1997 LT1/LT4 Engine Related

First scan today

Old 12-21-2014, 04:28 PM
  #1  
Registered User
Thread Starter
 
jayblev95's Avatar
 
Join Date: Sep 2014
Posts: 40
First scan today

Just did my first scan and wanted to see if someone could look it over and let me know if anything is out of sorts. I started it in the driveway and cruised down the road a few minutes to the highway where I did a full stop 0-70 some odd mph run. Im new to this and wanted to see how everything looked after my tune. Thanks a bunch. http://www.mediafire.com/view/63n3cr9m5n4ldc3

Only issues I know of is under WOT in second gear it has some slight hesitation sometimes but that's all. If I need to do a another scan under different variables( WOT, cruise, idle, etc....) just let me know also. Thanks again for taking a look.

Last edited by jayblev95; 12-21-2014 at 04:32 PM.
jayblev95 is offline  
Old 12-21-2014, 05:15 PM
  #2  
Super Moderator
 
Injuneer's Avatar
 
Join Date: Nov 1998
Location: Hell was full so they sent me to NJ
Posts: 67,294
Re: First scan today

I'll download it at work tomorrow and take a look at it.

How long have you been driving it since the tune was installed?
Injuneer is offline  
Old 12-21-2014, 07:52 PM
  #3  
Registered User
Thread Starter
 
jayblev95's Avatar
 
Join Date: Sep 2014
Posts: 40
Re: First scan today

A little over a month or so. Probably close to 2. Thank u for taking the time.
jayblev95 is offline  
Old 12-22-2014, 08:45 AM
  #4  
Super Moderator
 
Injuneer's Avatar
 
Join Date: Nov 1998
Location: Hell was full so they sent me to NJ
Posts: 67,294
Re: First scan today

You have problems.

What's OK:

-Idle speed, stock program values, steady

-IAC

-TPS

-MAF - a shade low at idle, but MAP is good. Check for a leak in the rubber elbow between the MAF and TB

-System Voltage - Generally healthy, but early in log is stays below 12V. Has the alternator ever been replaced? It does eventually catch up, and pushes the sytem voltage back above 13V.

IAT - readings are fine, but heat soak present on startup (100*F, vs 56*F at max air flow) Not a problem.

MAP - Very good vacuum.


What's not good:

-Knock retard 8.19* when you hit the throttle, because it's running very lean

-Long Term Fuel Trims (LTFT) - Adding a large amount of fuel in just about every cell

-Very lean in power enrichment mode - This is where you open the throttle, and the PCM switches to a richer target A/F mixture to make HP and torque. Yours goes DEAD LEAN. The Cell 15 LTFT's are 160L/160R, and the PCM is bumping up the Short Term Fuel Trims (STFT) to try and correct the extreme lean condition. The STFT's approach 200, meaning the LTFT's are adding 25% extra fuel, and the STFT's are adding even more for a total 0f 86% more fuel than the PCM would normally calculate.

Check your fuel pressure... I would guess it is either low, or the injectors are smaller than they system has been programmed for. Do you have stock injectors? I would suspect you do. Check the fuel pressure at idle, and out on the road under load.

And do not continue to make WOT pulls.... you could damage the engine. The lean condition would explain the hesitation.

There was a strange line of data at 16:40:27. I removed that, since most of the data made no sense. That could have been some sort of interference (e.g. high voltage) on the ALDL system.
Injuneer is offline  
Old 12-22-2014, 09:10 AM
  #5  
Registered User
Thread Starter
 
jayblev95's Avatar
 
Join Date: Sep 2014
Posts: 40
Re: First scan today

They are stock injectors as far as I know. Im pretty sure they are. What is the readings I should be looking for when it comes to fuel pressure at idle and under load? And definitely no more WOT until this is corrected. I know you will need the fuel pressure readings before you give a definite answer but would be a fix for this? retune? Thank you so much for taking the time to go over this. Just FYI, Im pretty sure the plugs are worn and possibly the wires. Didn't know if that would make a difference. The alternator has been replaced. I see a rebuild sticker on it. It drops down when at idle but picks back up as soon as it comes off idle. Not sure if someone put an underdrive pulley on or if the alternator is going south on me.
jayblev95 is offline  
Old 12-22-2014, 10:42 AM
  #6  
Super Moderator
 
Injuneer's Avatar
 
Join Date: Nov 1998
Location: Hell was full so they sent me to NJ
Posts: 67,294
Re: First scan today

The reason I suspect a fuel pressure problem is that as the load on the engine increases (as indicated roughly by the Cell #), the LTFT's get larger. For example, at idle (Cell 16), the LTFT's are 143L/136R. By the time you get to Cell 9 they are 160L/146R, and then at max load, max RPM (Cell 15) they are 160L/160R.

An outside chance would be a large tear in the inlet elbow, allowing a significant amount of air to bypass the MAF sensor. But I don't see an irrationally low MAF reading when you took it up to 5,800 RPM.

Fuel pressure:

At idle, remove the vacuum compensation line from the fuel pressure regulator. Hold your finger over the line to prevent a vacuum leak. Pressure at idle should be 43.5 PSI, with GM accepting anything within the range of 41 - 47 PSI.

Still at idle, reconnect the vacuum line to the FPR. Pressure should drop proportional to intake manifold vacuum. Your pressure should drop about 8 PSI from whatever it reads without the vacuum line connected.

Tape the pressure gauge to the windshield, and take it out on the road. Normally, you would take it up to WOT and over 5,000 RPM. Under those conditions, pressure should not drop more than 2 PSI below the "no vacuum" reading you had at idle. Since you are possibly running very lean at WOT, you are going to have to see what it reads at say 75% throttle, at maybe 4,000 RPM. If it's starting to run short on fuel, the pressure will start to fall off as load increases. Maybe one test at WOT/5000 RPM, because it appears that the PCM was able to pull enough timing to prevent detonation.

If fuel pressure is low, check the filter, the fuel pressure regulator, and finally the pump. This would not be a problem that you would cure with a tune.
Injuneer is offline  
Old 12-22-2014, 10:51 AM
  #7  
Registered User
Thread Starter
 
jayblev95's Avatar
 
Join Date: Sep 2014
Posts: 40
Re: First scan today

Will do. I have a long weekend and sounds like perfect time to do this. I drove it today to work, will it be okay to drive just normal cruising or should I park it immediately until fixed. Either way is fine, I just have to run some errands today after work and I don't want to hurt it. I can just go home and get my DD if need be. Another thing I noticed, I will need to retune because I wanted the shift points at WOT to be at 5300 rpm. But it seems that's its going over that by quite a bit it seems. I thought that the factory tach was off a little but looking at the scan confirms that its way past where I want it. Like I said I know a lot about cars but the computer aspects of it are new to me.

Last edited by jayblev95; 12-22-2014 at 10:55 AM.
jayblev95 is offline  
Old 12-22-2014, 03:28 PM
  #8  
Super Moderator
 
Injuneer's Avatar
 
Join Date: Nov 1998
Location: Hell was full so they sent me to NJ
Posts: 67,294
Re: First scan today

The PCM is correcting the lean condition, so driving it under moderate load shouldn't be a problem.
Injuneer is offline  
Old 12-22-2014, 08:03 PM
  #9  
Registered User
Thread Starter
 
jayblev95's Avatar
 
Join Date: Sep 2014
Posts: 40
Re: First scan today

Thanks. I will do the fuel pressure test this weekend and get back to you.
jayblev95 is offline  
Old 01-05-2015, 07:00 AM
  #10  
Registered User
Thread Starter
 
jayblev95's Avatar
 
Join Date: Sep 2014
Posts: 40
Re: First scan today

Just an update. I changed the fuel filter. From the looks of it it was on there for a very, very long time. When I took it off I wiped off the non threaded end and tried to blow thru it and it had a lot of resistance, especially compared to the new one. I took the car out and noticed that it ran better and idled better. I did do a scan and was planning on posting it here but me being the "genius" that I am ( sarcasm) unplugged everything first before I saved it and the file was gone. So I will do another scan and post it here in the next few days. I was planning on doing the fuel pressure test but I already had the filter so I figured why not go ahead and put it on and see from there.
jayblev95 is offline  
Old 01-05-2015, 03:36 PM
  #11  
Member
 
GaryDoug's Avatar
 
Join Date: Jul 2010
Location: Florida West Coast
Posts: 1,230
Re: First scan today

You can set the "Auto-save scan file" checkbox on the engine tab to automatically save your scan as you go. It will slow the scan a bit, but you won't have to remember to save it at the end.
GaryDoug is offline  
Old 01-06-2015, 07:29 AM
  #12  
Registered User
 
Not Dave's Avatar
 
Join Date: Sep 2014
Location: Coupland, TX, USA
Posts: 119
Re: First scan today

Jayblev, it would be great if it were a restrictive fuel filter. Besides the broken trans mount the fuel filter was the 2nd thing I changed on the car when I picked it up from the previous owner. It looked old. Car ran fine but you never know. Hope that fixes your problem. A new fuel pressure regulator, if yours is bad, at least is a minor thing too.
Not Dave is offline  
Old 01-06-2015, 01:13 PM
  #13  
Registered User
Thread Starter
 
jayblev95's Avatar
 
Join Date: Sep 2014
Posts: 40
Re: First scan today

I will have to check that auto save feature. Thanks for the tip. And yes I hope that the filter is the only issue but I guess I will find out for sure on my next scan. Now on to my next few fixes for it. Namely spark plug and wire change( not looking forward to it), and Im pretty sure is a rear main oil seal leak. Fun Fun
jayblev95 is offline  
Old 01-06-2015, 01:52 PM
  #14  
Super Moderator
 
Injuneer's Avatar
 
Join Date: Nov 1998
Location: Hell was full so they sent me to NJ
Posts: 67,294
Re: First scan today

Before your next data log, clear the long term fuel corrections. Pull the "PCM BAT" fuse for 30 seconds. That way we can watch how (or if) the PCM starts to change the LTFT's from the default value of 128.
Injuneer is offline  
Old 01-07-2015, 06:45 AM
  #15  
Registered User
Thread Starter
 
jayblev95's Avatar
 
Join Date: Sep 2014
Posts: 40
Re: First scan today

Will do. I should be able to do a scan this weekend at the latest. Have some bad weather moving in and wont be driving it for a few days.
jayblev95 is offline  

Thread Tools
Search this Thread
Quick Reply: First scan today


Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.