LT-1 issue - Page 5

Alan Roehrich · 04-15-2015, 09:27 AM

Kirk is correct, there is no substitute for genuine OE sensors. I will not use cheap aftermarket crap, it's nothing but trouble. Most systems use easy to find GM parts. Rock Auto usually has them.

buzzinhalfdozen · 04-15-2015, 10:16 AM

John, you should see no change in the reference voltage to the MAP sensor with it plugged in. You should have 5 volt in (reference) low reference (ground) and your signal back to the ECU. Just for grins can you back out your signal wire leaving only the 5 volt and ground wires and retest by plugging MAP back in and see if voltage drops, just to make sure the feed back wire isn't shorted to ground somehow, be it actually touching ground or an issue in the ECU itself. Of course test resistence on the ground circuit from sensor plug to ground, not sure if that would be chassis ground or ECU provided.Other than that are you certain the MAP sensor is pinned correctly? My bet is that the MAP sensor is incorrectly wired. As alot of systems use the GM type 1 BAR MAP sensor the correct pinout would be A-ground B-signal C- 5 volt reference.

John Nechiporchik · 04-15-2015, 11:52 AM

We did not change the wiring on the MAP connector. But I will test as suggested.
I just started it again with the old MAP sensor and let it idle until it warmed up. It idles smooth as silk and slowly accelerating the engine went to 2500 and started coughing and sputtering.
I am scheduling an appointment with a local tuner (Watson Engineering). I spoke with the guy there today who does the FAST installations and tuning. He said he will perform the diagnosis to determine if the issue is in the sensors or the ECU.
They are a top notch shop and 5 miles away. He has the appropriate testing tools to perform the tests suggested by the guys on here.

I appreciate all the help thus far.... I'll update the thread when I have new information.
I'm preparing my CFO (wife) for a potential new engine management system......

Thanks,

John

jimmyparker · 04-15-2015, 12:42 PM

John, just a thought, have you tried running the motor with the alternator disconnected?

John Nechiporchik · 04-15-2015, 12:58 PM

Jimmy, Yes it is currently disconnected.

Thanks

Ed Wright · 04-15-2015, 04:35 PM

Get a FAST system if the ECU has a weak driver, which is what I suspect is the problem.

John Nechiporchik · 04-16-2015, 08:24 PM

After every possible test I could run, tonight I pulled the ECU out of the car to send it to an Accel Service tech in Alabama. When I talked to him, I said I had a spare non crank trigger ECU that I would send along for parts etc. It occurred to me that the low voltage issues were happening on circuits that were likely independent of the crank trigger. So, I plugged the spare in and the low voltage problem went away.5.1V with a fully charged 16 V battery.
Thanks to Alan and a few others for being diligent about tracking this down.
The good news is I believe we have the true root cause. The TBD news is can we get one good ECU out of the 2 on their way to Alabama.
I'll update when I get more info. Likely sometime next week.
Thanks again for all the input.

John

Ed Wright · 04-17-2015, 07:39 AM

That would be the weak driver in the ECU I mentioned.

John Nechiporchik · 04-17-2015, 09:11 AM

Ed, That's correct. I appreciate your input in identifying this issue.
Given your experience with these cars, do you feel the weak driver was the sole contributor or could there still be a possibility the rotor phasing is an issue as well ?
Thanks

Mike Savelle · 04-17-2015, 04:13 PM

John I was unable to find the accell unit I had , sorry but I'm sure you are on the right track . Mike

04-15-2015, 09:27 AM	#41
Alan Roehrich Veteran Member Join Date: May 2006 Location: Murfreesboro TN Posts: 5,124 Likes: 1,581 Liked 1,875 Times in 422 Posts	Re: LT-1 issue Kirk is correct, there is no substitute for genuine OE sensors. I will not use cheap aftermarket crap, it's nothing but trouble. Most systems use easy to find GM parts. Rock Auto usually has them. __________________ Alan Roehrich 212A G/S

04-15-2015, 10:16 AM	#42
buzzinhalfdozen Senior Member Join Date: Sep 2006 Location: Bellevue Ohio Posts: 984 Likes: 0 Liked 11 Times in 8 Posts	Re: LT-1 issue John, you should see no change in the reference voltage to the MAP sensor with it plugged in. You should have 5 volt in (reference) low reference (ground) and your signal back to the ECU. Just for grins can you back out your signal wire leaving only the 5 volt and ground wires and retest by plugging MAP back in and see if voltage drops, just to make sure the feed back wire isn't shorted to ground somehow, be it actually touching ground or an issue in the ECU itself. Of course test resistence on the ground circuit from sensor plug to ground, not sure if that would be chassis ground or ECU provided.Other than that are you certain the MAP sensor is pinned correctly? My bet is that the MAP sensor is incorrectly wired. As alot of systems use the GM type 1 BAR MAP sensor the correct pinout would be A-ground B-signal C- 5 volt reference. __________________ Joe Buchanan SS/BX 3117 Last edited by buzzinhalfdozen; 04-15-2015 at 11:13 AM.

04-15-2015, 11:52 AM	#43
John Nechiporchik Member Join Date: Mar 2007 Location: Grosse Ile Mi. Posts: 316 Likes: 84 Liked 13 Times in 7 Posts	Re: LT-1 issue We did not change the wiring on the MAP connector. But I will test as suggested. I just started it again with the old MAP sensor and let it idle until it warmed up. It idles smooth as silk and slowly accelerating the engine went to 2500 and started coughing and sputtering. I am scheduling an appointment with a local tuner (Watson Engineering). I spoke with the guy there today who does the FAST installations and tuning. He said he will perform the diagnosis to determine if the issue is in the sensors or the ECU. They are a top notch shop and 5 miles away. He has the appropriate testing tools to perform the tests suggested by the guys on here. I appreciate all the help thus far.... I'll update the thread when I have new information. I'm preparing my CFO (wife) for a potential new engine management system...... Thanks, John

04-15-2015, 12:42 PM	#44
jimmyparker Member Join Date: Oct 2009 Location: columbus, georgia Posts: 385 Likes: 66 Liked 309 Times in 88 Posts	Re: LT-1 issue John, just a thought, have you tried running the motor with the alternator disconnected?

04-15-2015, 12:58 PM	#45
John Nechiporchik Member Join Date: Mar 2007 Location: Grosse Ile Mi. Posts: 316 Likes: 84 Liked 13 Times in 7 Posts	Re: LT-1 issue Jimmy, Yes it is currently disconnected. Thanks

04-15-2015, 04:35 PM	#46
Ed Wright Veteran Member Join Date: Mar 2005 Location: Sand Springs, OK Posts: 8,132 Likes: 896 Liked 390 Times in 170 Posts	Re: LT-1 issue Get a FAST system if the ECU has a weak driver, which is what I suspect is the problem. __________________ Ed Wright 4156 SS/JA

04-16-2015, 08:24 PM	#47
John Nechiporchik Member Join Date: Mar 2007 Location: Grosse Ile Mi. Posts: 316 Likes: 84 Liked 13 Times in 7 Posts	Re: LT-1 issue After every possible test I could run, tonight I pulled the ECU out of the car to send it to an Accel Service tech in Alabama. When I talked to him, I said I had a spare non crank trigger ECU that I would send along for parts etc. It occurred to me that the low voltage issues were happening on circuits that were likely independent of the crank trigger. So, I plugged the spare in and the low voltage problem went away.5.1V with a fully charged 16 V battery. Thanks to Alan and a few others for being diligent about tracking this down. The good news is I believe we have the true root cause. The TBD news is can we get one good ECU out of the 2 on their way to Alabama. I'll update when I get more info. Likely sometime next week. Thanks again for all the input. John

04-17-2015, 07:39 AM	#48
Ed Wright Veteran Member Join Date: Mar 2005 Location: Sand Springs, OK Posts: 8,132 Likes: 896 Liked 390 Times in 170 Posts	Re: LT-1 issue That would be the weak driver in the ECU I mentioned. __________________ Ed Wright 4156 SS/JA

04-17-2015, 09:11 AM	#49
John Nechiporchik Member Join Date: Mar 2007 Location: Grosse Ile Mi. Posts: 316 Likes: 84 Liked 13 Times in 7 Posts	Re: LT-1 issue Ed, That's correct. I appreciate your input in identifying this issue. Given your experience with these cars, do you feel the weak driver was the sole contributor or could there still be a possibility the rotor phasing is an issue as well ? Thanks

04-17-2015, 04:13 PM	#50
Mike Savelle Member Join Date: Dec 2001 Location: Ontario Canada Posts: 369 Likes: 125 Liked 7 Times in 5 Posts	Re: LT-1 issue John I was unable to find the accell unit I had , sorry but I'm sure you are on the right track . Mike