LT-1 issue
 

Fired up LT-1 after rebuild and all appeared to be well. At initial start up, only ran the engine to around 2500RPM.
Loaded up and went to track.
At track, warmed up and drove to tech and back to trailer. went to 3000and all was well
After adding fuel to cell and a quart of trans fluid, headed to lanes. Car would not accelerate driving to lanes, headed back to trailer.
As it sits now, car will start, idle, and immediately stumble as the throttle is opened...like it is not getting fuel.
Gas was a new sealed container of renegade 110+
Fuel map same as last year
Rebuild included new rings, bearings, cam, valve springs and a different set of heads.
Before initial start, I flushed the fuel system and replaced the fuel filter.
Looking for possible causes.
Bad fuel?
Throttle position sensor?
Any ideas??
Thanks for any help.

John

Re: LT-1 issue
 

what was the fuel pressure at ?

Re: LT-1 issue
 

You didn't mention anything about timing. Have you checked it? If so, where is it?

What engine management system are you using?

Re: LT-1 issue
 

Fuel pressure at 45psi. We did notice that the fuel pressure gauge seemed to drop more quickly once the engine was shut off. Typically, the reading on the gauge very slowly declines after shut off of system.
The timing is set at 42 degrees and I have an old style Accel Cal Map system.

Thanks.

Re: LT-1 issue
 

Make sure the MAP sensor wiring, and sensor is OK. If you removed the sensor, from last year, make sure the seal to the intake is in good condition.

Re: LT-1 issue
 

I'll check that . I did remove it since last year.

Re: LT-1 issue
 

Use a OHMS meter and sweep test the TPS sensor.

Re: LT-1 issue
 

If the fuel pressure drops fairly soon and/or quickly after you shut the vehicle off, you need to test fuel pressure and volume, as well as determine whether or not the fuel pump used has a check valve. If fuel pressure did not drop when the car ran before, but does now, I suspect the pump is supposed to have a check valve, and there is now a problem.

Re: LT-1 issue
 

Broken ignition rotor.

Re: LT-1 issue
 

Dyno, Brand new MSDcap and rotor.
Alan, How would a faulty check valve in the pump react?
Will check the TPS for sweep again. Checked it in the fall and it was OK.

Re-terminated 3 TPS leads as the old terminals seemed loose. This did not solve problem. Also pulled back timing to 36......no difference.

Re: LT-1 issue
 

The check valve retains fuel pressure after the pump is turned off. For example, a stock or stock replacement pump will usually retain 90% or so pressure for several minutes. If your pump retained a significant amount of pressure last year, for a significant period of time, and this year it bleeds off a substantial amount of pressure fairly quickly, then something significant has changed. Since that change is accompanied by a performance/driveability problem, that is where you should look first.

I would think, and I may be wrong, that 45 psi is a little low. It would seem to me that you'd want to run closer to 55-60 psi if you can build that much pressure, and use a shorter duty cycle on the injector to maintain the A/F ratio the engine likes.

Re: LT-1 issue
 

Every problem I had with my LT-1 was the opti spark

Re: LT-1 issue
 

Alan, Thanks for the info. I'll pull the fuel pump as soon as I finish my analysis on the Optispark question (below)
I tested the TPS with the following results:
Per the Accel manual, the input signal is 5V.

Input signal was 3.32 Volts (issue??)
.48 Volts at idle
1.74 at mid throttle
2.67 volts at WOT.

I tested a spare throttle body /TPS and got almost identical results.

Dyno/Lee: On the last pass I made last year, I destroyed the stock style rotor.It literally shattered in the shutdown area.
Over the winter, I replaced the cap and rotor with MSD parts.
Is it possible that the catastrophic failure caused some damage to the distributor itself that is resulting in this condition? All input appreciated.

Re: LT-1 issue
 

John,
Yes, reference voltage to the TPS being under 5.0 vdc is a serious problem, especially being almost 1.7 vdc low. When you are testing that voltage, is the connector disconnected and the battery voltage at 12.5 vdc or above? Is the battery input voltage at the ECU 12.5 vdc or above?

Yes, it is possible that a shattered rotor damaged the distributor.

Re: LT-1 issue
 

What about crank trigger sensor?

Re: LT-1 issue
 

Alan, When we re terminated the TPS connector, we added a testing port (connector) so I am able to test it with the harness connected to the TPS and the ECU harness. The battery is a 16 V that measured 16.85 volts with ignition on.

What do you think could have been damaged in the distributor housing itself?
Need to check voltage at ECU

Re: LT-1 issue
 

John,
Right now, what is important is the voltage on the battery supply terminal at the ECU? Especially with the engine started and running.

There could be any number of problems caused by binding, flying debris, etc, inside your distributor.

Re: LT-1 issue
 

If you never welded the shaft in the opti spark it may have moved making the phasing wrong for the crank trigger,try another distributor

Re: LT-1 issue
 

Thanks for all the info. Will continue the investigation tomorrow.

Re: LT-1 issue
 

low voltage

Re: LT-1 issue
 

You would be extremely lucky to find a dead spot on the TPS wiper with a volt/ohm meter. They are too slow. What you see on a digital meter is not real time. It is data frames, like frames on a movie film. The update rate with a meter is so slow, sweeping the TPS usually falls between data frames. You would have to move the throttle lever VERY slow to catch it with a meter. Thing to use is a fast digital lab 'scope. I always used a Fluke 98A. Very fast. Still need to sweep the TPS 15 or 20 times to be sure there is no issue there.

Stock fuel systems will hold fuel pressure a long time after the key is shut off. Factory fuel pumps have check valves. Not so aftermarket race pumps. My Aeromotive system drops pressure quickly. I wait a couple seconds after turning it on to crank the starter. Much shorter crank times if I wait for fuel pump to get the pressure up.

Problem is likely TPS, MAP related, or a tuning issue.

Re: LT-1 issue
 

Once a LT-1 I had built was acting weird backfire some would'nt idle, long story short,
found rotor out of phase was almost half way between cylinders and optical sensor showed out of range,probably had slipped on shaft,I slotted the wheel and got the opti sensor in range and slotted rotor and phased it ran good then.
When rotor etc exploded could have knocked out of phase,I used a small degree wheel to turn engine to where ignition timing was so I could check phasing of rotor
Mike Taylor 3601

Re: LT-1 issue
 

Sheep Boy can't post here, but thinks you may have a rubber fuel line deteriorating inside, putting crap in your injectors. If you have old stuff on your car, it sure would be worth checking.

Re: LT-1 issue
 

Will do. Flushed fuel system prior to start-up.
May be good idea to do it again and check volume after the regulator.
What is the process to inspect individual injectors once removed from fuel rail?

Thanks,
John

Re: LT-1 issue
 

Look for debris in the screen in the top of the injectors.

Re: LT-1 issue
 

John, not sure on your system but most I've seen have 5 volt reference to TPS as someone stated earlier not having the 5v volts would be a problem. Can you not view live data with a laptop on your system? If so use that to look at what the ECU is seeing in relationship to any and all sensors. I had this very thing on my set up a few years ago and it was a loose terminal in my TPS plug, it would read at times then drop out and the engine would hardly move the car. Also not sure but some systems you can calibrate most of the sensors including the TPS. Since the main inputs used for timing and fuel are the MAP and TPS, (there are others but less important as to throttle responce) I'd look closely at both those. BTW engine off does the MAP and BARO sensors read the same, and what is MAP reading with engine running?

Re: LT-1 issue
 

After thrashing on this beast all day, checking all the items that were suggested, it appears that going thru the valve train and re-lashing the valves was the primary contributor.
I installed a new cam this winter with the "shimmed" lifters and appears I adjusted them too snug...and 4 valves (2 Ex and 2 In) were extremely over adjusted. So I went thru the system and re- set them all until "0" lash.
Fired it up and idled like a dream....revved it up slowly and with the exception of a slight flat spot around 3000RPM, it revved right up to 7000. I'm thinking (Ed, the tune up)needs to be tweeked for the new components. Tomorrow we'll hook the lap top up and see if we can work on the flat spot.
I'm thinking it's time to make an appointment with the chassis dyno guy to see if we can fine tune this thing.

I hope I'm done on this issue. Thanks to all of you for your ideas and support.

Special thanks to Russ Abrams for the all day text message and phone call support.

John

Re: LT-1 issue
 

mind if I ask what brand lifter you used?
Thanks

Re: LT-1 issue
 

Stock GM lifters modified by Tom Russell.

Re: LT-1 issue
 

Glad to hear you're making progress John. Be sure and fix your voltage problem before you spend dyno time and money, you don't want to spend time and money on a system that is not working correctly. Make it all work correctly first, then hit the dyno. Good luck.

Re: LT-1 issue
 

Thanks Alan. That is on the agenda.

Re: LT-1 issue
 

Following up on Alan's advise to track down the voltage loss at the TPS, I contacted a guy that Accel advised as a service rep for their product. I spoke to him several time last year when I was experiencing a no start condition and he was helpful
As I explained my low voltage to the TPS, he suggested unplugging the MAP sensor (which was getting a 5v input) and then checking the TPS input. Well, with both connectors disconnected (TPS and MAP), both input voltages from the ECM read 4.97 volts. When I installed the MAP sensor connector, the voltage to the TPS dropped back to 4.24V.
I checked the ECM ground which is directly to the battery and the ground from the rear of the cyl. head and all were clean and tight.
Would a defective MAP sensor cause excessive current draw and subsequently weaken the TPS input?? Not certain how that stuff works. The accel guy indicated the two circuits , although different pins in the ECM connector, have the same voltage reference source.
He indicated a ground problem or possibly a bad MAP sensor.

All input/experience appreciated.

John

Re: LT-1 issue
 

Update: The above tests were run with the battery at 17V.

Here's a matrix to clarify test results:

Both connectors attached: 3.75V TPS 3.75V MAP

TPS connected/MAP disconnected: 5.0V TPS 5.0V MAP

TPS disconnected/MAP connected: 4.2V TPS 4.2V MAP

Both disconnected : 5.0V TPS 5.0V MAP

Hopefully someone can make some sense out of this. The MAP sensor appears to be having the negative influence on the system.
Help!!

Thanks,

John

Re: LT-1 issue
 

Simply substitute another MAP sensor and re-test.

Re: LT-1 issue
 

John,
Do you have some sort of step down transformer/transistor reducing the voltage to your ECU to somewhere around 13.5 vdc, or is it happy with being supplied with 17 vdc? The reason I ask is that some ECU's do not like excessive voltage, and their internal regulators are not designed to deal with more than 14 vdc or so.

Re: LT-1 issue
 

Alan, The ECU is seeing direct voltage from 16volt battery.....typically 16.8 - 17 volts.
This set-up was in the car when I got it. The Accel support guy and I did not discuss this...but I will follow up and ask him.

John

Re: LT-1 issue
 

Installed new MAP sensor and the previous voltage of 3.75 dropped to 1.54 volts at the input side on both the MAP and TPS connectors.
For info purposes, I measured the resistance between the B and C terminals (volts in /signal out) on both MAP sensors with the following result:
Old sensor : 343
New sensor: 24 (is this a reject?) INFO CORRECTED FROM ORIGINAL POST. Had the numbers switched

Anyone have a reference number for this resistance??
Thanks,

John

Re: LT-1 issue
 

Umm ..... just a thought. The wire's didn't get mixed up did they ?

Re: LT-1 issue
 

No they did not,

Re: LT-1 issue
 

When MAP sensors were common place and needed replacement we went with OEM. I had quit a few MAP and ECT sensors that weren't even close to specs. Like Ed said you need a good DVO meter to check for some problems. I use a Fluke 88 I have had for about 20 years. Not all MAP sensors have the same BAR specs as the vacume changes.

Kirk