LT1 No Start Condition - Lots of test completed
08-23-2013, 08:25 AM
#1
LT1 No Start Condition - Lots of test completed I’ve recently completed my 1994 LT1 (OBD1) 383 motor project. The car was broke in on the dyno and tuned, ran great for 144miles total. It sat at an idle the other day for a minute or so, I put the car in 1st gear & a few feet later, under very light acceleration, the car sputtered several times and stalled. It has yet to start again.
My first observation was, the fuel pressure gauge drops to zero in less than 5 seconds after the pump primes, when the ignition is turned to the run position (car not running). If you engage the starter, after the pump primes & the gauge falls to zero, the line pressure will immediately climb to 45psi & holds, until you disengage the starter, at which time it falls back to zero.
Despite having a new Walbro 255 pump in the tank, I took advise from another post, that sometimes the check valve (internal to the Walbro pump) will fail, allowing fuel to bleed back to the tank. I put another brand new pump in the car, and had no change in the end result.
I pressurized the fuel rail, off the car to ensure my regulator was holding 45psi, and allows fuel to pass through at pressures above. No leaks on the rail and the regulator functioned properly.
I used a noid light to ensure the injectors were receiving a trip signal from the ECM. All 8 check out. The pink wire on all 8 injector plugs hold a very consistent 12.18v, read off a Fluke meter. The mixed color lines on each injector plug, showed no signs of ground continuity, with & without the ignition turned to the run position. All of the engine and ECM ground wires also test out fine as well.
I test fired the injectors in the fuel rail, but out of the intake, so we could see each spray. The pattern was consistent and clean when the starter was engaged. There was no sign of fuel leaking or sticking injectors, during the almost immediate drop in fuel pressure after the starter was disengaged.
I put a second ECM in the car, which was test fired in a friend’s car to ensure it was good. No change in FP, and the car still makes no attempt to start. If you engage the starter for 10 to 12 seconds, once you allow the key to return to the run position (car not running at this point), it will sputter a couple times, much like an old carburetor would diesel upon shutdown. If you run a constant 12v to the fuel pump, it will hold the gauge pressure at 45psi, and the regulator will pass fuel to the tank on the return line.
The car has a brand new Jegs brand OPTI spark distributor in it (changed less than 15miles ago, after my first Jegs unit failed). To rule out an ignition problem, we left the #4 plug in the cylinder (all 8 plugs were changed after tuning and still clean at this point), pulled the spark plug wire off and inserted a new plug to the wire boot, laid it on the header and turned the key to initiate the starting sequence. The plug produced a very strong and consistent blue spark.
I’ve read the ECM with my laptop, and the car is not reporting any trouble codes.
Suggestions??? I've spent a couple hours testing and reading other posts.
My next step I guess, is to bring the car up to TDC on cylinder 1 and then remove and disassemble the opti to see if it jumped time.
My first observation was, the fuel pressure gauge drops to zero in less than 5 seconds after the pump primes, when the ignition is turned to the run position (car not running). If you engage the starter, after the pump primes & the gauge falls to zero, the line pressure will immediately climb to 45psi & holds, until you disengage the starter, at which time it falls back to zero.
Despite having a new Walbro 255 pump in the tank, I took advise from another post, that sometimes the check valve (internal to the Walbro pump) will fail, allowing fuel to bleed back to the tank. I put another brand new pump in the car, and had no change in the end result.
I pressurized the fuel rail, off the car to ensure my regulator was holding 45psi, and allows fuel to pass through at pressures above. No leaks on the rail and the regulator functioned properly.
I used a noid light to ensure the injectors were receiving a trip signal from the ECM. All 8 check out. The pink wire on all 8 injector plugs hold a very consistent 12.18v, read off a Fluke meter. The mixed color lines on each injector plug, showed no signs of ground continuity, with & without the ignition turned to the run position. All of the engine and ECM ground wires also test out fine as well.
I test fired the injectors in the fuel rail, but out of the intake, so we could see each spray. The pattern was consistent and clean when the starter was engaged. There was no sign of fuel leaking or sticking injectors, during the almost immediate drop in fuel pressure after the starter was disengaged.
I put a second ECM in the car, which was test fired in a friend’s car to ensure it was good. No change in FP, and the car still makes no attempt to start. If you engage the starter for 10 to 12 seconds, once you allow the key to return to the run position (car not running at this point), it will sputter a couple times, much like an old carburetor would diesel upon shutdown. If you run a constant 12v to the fuel pump, it will hold the gauge pressure at 45psi, and the regulator will pass fuel to the tank on the return line.
The car has a brand new Jegs brand OPTI spark distributor in it (changed less than 15miles ago, after my first Jegs unit failed). To rule out an ignition problem, we left the #4 plug in the cylinder (all 8 plugs were changed after tuning and still clean at this point), pulled the spark plug wire off and inserted a new plug to the wire boot, laid it on the header and turned the key to initiate the starting sequence. The plug produced a very strong and consistent blue spark.
I’ve read the ECM with my laptop, and the car is not reporting any trouble codes.
Suggestions??? I've spent a couple hours testing and reading other posts.
My next step I guess, is to bring the car up to TDC on cylinder 1 and then remove and disassemble the opti to see if it jumped time.
08-23-2013, 09:37 AM
#3
I did not. I was assured that the use of Loctite was part of the manufacturing process, after several production lots had failures where the rotor button screws would back out.
I didn't want to disrupt the internals to validate the statement. It came right out of the box, and on to my motor after a quick visual inspection and twist of the cam driveshaft slot to make sure there was no drag or excessive play.
I didn't want to disrupt the internals to validate the statement. It came right out of the box, and on to my motor after a quick visual inspection and twist of the cam driveshaft slot to make sure there was no drag or excessive play.
08-23-2013, 12:04 PM
#5
Is it worth the effort to roll the motor over to #1 TDC before I remove the OPTI? If it is a timing issue caused by another OPTI failure, I'd be curious to see what cylinder its firing on.
Does the fuel pressure drop seem inherent to the LT1 though? Maybe I've never noticed that before and its actually nothing to be concerned with or investigate further.
Does the fuel pressure drop seem inherent to the LT1 though? Maybe I've never noticed that before and its actually nothing to be concerned with or investigate further.
08-23-2013, 02:02 PM
#6
You cannot mess up the timing on an lt1 opti. When you take the cap off or the sensor wheel, they both will only line up one way. The spline drive and roll pin drives only go in one slot. I wasted two MSD optisparks from the screws coming out, I made them fix both of them under warranty.
08-25-2013, 12:01 PM
#7
You boys were spot on. Pulled the front end of my motor apart, and removed the OPTI. After just 8 miles (no passes at the track), it looked like an assembly operator pulled the pin on grenade, and closed the lid and put it in the box! Just a shame that you have to take a brand new part, out of the box & loctite the screws so it doesn't go in to self distruct mode! thanks to those who posted here! The car starts and runs strong, just as it did 8 short miles ago....LOL
