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.

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.

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

Re: LT-1 issue
 

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

Re: LT-1 issue
 

Jimmy, Yes it is currently disconnected.

Thanks

Re: LT-1 issue
 

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

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

Re: LT-1 issue
 

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

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

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

Re: LT-1 issue
 

Thanks for checking Mike.

Re: LT-1 issue
 

Update: Got the verdict back from the guy who tested my ECU and determined it was no good.
The second, non crank trigger unit I sent was OK.
My options are: Use the non crank trigger Accel unit and dis able the existing crank trigger and activating the Optispark........ or bite the bullet and install a FAST system.
I'm not inclined to use the Accel as it is just more "old stuff". But, a lot less costly.
I would like to hear from someone that has installed an XFI 2.0 on an LT1 and get a clear understanding on utilizing the optispark sensor and disc as the cam sensor for the XFI.....and what modifications, if any, are required to the disc. I'd like a better understanding of the installation process before I proceed.
Thanks . I'm sure I'll have additional questions.

John

Re: LT-1 issue
 

I have a FAST XFI on my LT1. Had the Optispark on it when it originally an LT1 block. Slung the blades off the rotor right away. Learned to remove those two plastic pegs holding the two piece rotor blade in place. Drilled the rotor for and installed two long 1/8" aluminum pop rivets to hold the blades in place. No more rotor coming apart problems. MSD now makes a rotor with screws holding it together. FAST has instructions for triggering it with the Opti if you want. I use an MSD crank trigger. FAST also has their own crank trigger now. Not at the time Input my mess together.

Re: LT-1 issue
 

Ed, I have an MSD crank trigger on the car now. Also have an MSD cap and rotor on the opti. My question relates to using the Optispark disc/sensor to activate the cam position signal with the XFI system. It appears that FAST makes a wiring harness that plugs into the opti that provides the signal for the sequential injection. There is no mention in the instruction relative to any modifications that need to be made to the opti disc (wheel). That is what I would like to know.

John

Re: LT-1 issue
 

There is a way, can't remember how they did it. Maybe David Page will see this. Seems like guys are covering all but one slot? If you don't have 8 wide bands so you can adjust individual cylinders, there is no real reason for sequential modd.

Re: LT-1 issue
 

John,
You need to talk to Kevin at FAST. Tim Cole at Comp sent me to him, he will take great care of you, before, during, and after the sale.

Re: LT-1 issue
 

Ed, I understand your comment about 8 wide bands and I am not planning on that expense.
Can the XFI system be run in batch mode?
Also, Maybe I would be better off looking into the new FAST Sportsman unit.

John

Re: LT-1 issue
 

PM sent

Re: LT-1 issue
 

Also, maybe I should also look at Big Stuff. Anyone running there stuff on LT1?
Thoughts/input??

John

Re: LT-1 issue
 

You can run the crank trigger completely independent from the ECU. I ran mine that way and just ran locked timing with a MSD 7 and later a digital 6. Accel GEN VII. Sure there's power to be gained in sequentual mode but it takes a lot to make that happen. I ran one wire from the ECU to the MSD and ran the crank trigger just like a non EFI race engine. MSD cap and rotor and optispark guts removed.

Re: LT-1 issue
 

Only way there is more power in Sequential Modevis tuning each cylinder individually. Of course, otherwise it runs in Batch Fire. And how much depends on how far your cylinder-to-cylinder fueling and spark is.
BS3 runs just fine on an LT1. A friend of mine is running that on his.I have worked with BS3, ACCEL DFI, GM's MEFI, and Holley (both old & new systems) and I much prefer FAST. Holley's new system would be my second choice. I'm not going into it here, but I can make FAST XFI do something I can't make the others do. Maybe the new Holley, if I had the time.

Re: LT-1 issue
 

Update # 2:
After much discussion and several adult beverages to assure clear thinking.....Today I spent the big bucks and got a FAST XFI 2.0 system coming my way.
Hopefully my next update will report on a satisfactory outcome to this issue.
Thanks for everyone's input.

John

Re: LT-1 issue
 

Good move John.

Re: LT-1 issue
 

John, I a little late to the party here but Ill offer what I know.
The Optispark adapter harness that we (FAST) sell is made to allow you to use the Low Resolution ring on the disk as a crank trigger. This is what you would use on a street car if you did not want to go with a full blown external crank trigger. This would work OK if you were dead set on using the Opti for crank signals.

In your application, there are really only two good choices, first, you could run a crank trigger for crank signal, use the opti unit as a cap and rotor only, and run in bank to bank mode. While Sequential will offer some potential gains in idle quality and individual cyll tuning, I have several super stockers running bank to bank that run perfectly well, idle great, and are bad fast! The XFI 2.0 allows you to switch from Bank/Bank to Sequential anytime you wish.

Your second option has a few variables. You can do the same as above, but modify the opti to generate a cam signal. Wiring wise, you would need the Optispark Adapter harness we sell and you would have to move one wire in the harness. I can easily walk you through the necessary changes. The next part sounds hokey but it actually works pretty well. You can get some good quality foil tape and cover all the holes in the disk. Then, identify the position of the optical sensor when the crankshaft is at 60 - 120 degrees BTDC compression stroke. This is a very wide window where the XFI looks for a cam signal. You then poke out one of the holes in the Low Res ring on the disk so that the single open hole passes the optical sensor somewhere between 60 - 120 BTDC. This will generate your cam signal and allow proper sequential fueling.

I have seen some take and gut the inside of the Opti and make an aluminum wheel with a single magnet that runs off the stock opti distributor shaft. They then mount an MSD pickup to read off this wheel.

If you are interested in setting one of these methods up to run sequential, PM me and Ill walk you through it.

David Page
FAST

Re: LT-1 issue
 

pbp1 (David) you have a PM

Re: LT-1 issue
 

Installed the FAST XFI 2.0 system on the LT1 and fired it up today. Fired up on the first hit and appears to be running smoothly.
With a little luck, we will take it to Milan this week and get the calibration dialed in. I am fortunate to have a very experienced tuner that is helping me.
In addition, throughout the installation process I placed several calls to the FAST tech line and got outstanding support each time.

Hopefully, this chapter will be closed soon and the racing will begin!
John

Re: LT-1 issue
 

Good to hear John!

Re: LT-1 issue
 

Good move!

Re: LT-1 issue
 

Just in time for Norwalk !