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My 1994 chevy LT1 engine stopped while running. Testing found no ignition no fuelpump pressure. Does the computer have a shut down ability? I have replaced the ignition module, ignition coil and fuel pump. The fuel pump relay appears to be working. Help
PCM Ingition fuse?
I Checked PCM fuse. It is OK. Is the ignition and fuel pump linked thru the computer?
have you checked your oil pressure. when the oil pressure gets low the engine has a shut off for the fuel.
Check the ignition fuse to.
The oil pressure has been quite good on this engine. Where is the "low oil pressure fuel shut off switch"? Is there a test for it? I have a problem with the fact that the ignition and the fuel pump shut down at the same time.Quote:
Originally Posted by jyardgirl
I believe it's in the block back by where a traditional distributor would be. I should know this, I just rebuilt the motor in my wife's 95 Z28. I hope I remembered correctly!
Keith
you are right blwn. it is at the back of the engine.
Thanks for the help. The situation is complicated by the fact that the car stopped 75 miles from home. I have checked everything but the oil pressure switch. I am going to drive the 75 miles to visit my 94 Chevy Caprice station wagon. My concern was the way it stopped while running and both the fuel pump and the ignition are not working. It stopped as if I shut it off. Could that be the problem????????? It happened at night. The headlights remained on. The check engine light came on and I costed to a stop. The engine cranks.
Can I get to the wires comeing from the ignition switch to see if it is functioning? There are 4 wires comeing to the coil. Can I test at this point to see if the ignition switch is working? HELP
When you turn the key to the run position, you should hear the fuel pump come on then go off. Does that happen? Another question is how many miles on the currently installed Opti Spark? The Opti Spark is the distributor located under the waterpump. If the waterpump leaks, say goodby to the Opti! They are notorious for just quitting. How have you checked your ignition? Did you pull off a plug wire and crank or use a timing light? I would think without the luxury of a diagram, even if the oil pressure switch was bad it would at crank, start and then die.
Keith
When I turn the key to run position the fuel pump does NOT come on. The ignition was tested by pulling a plug grounding the plug and cranking the engine. I hope I can get the distributor off without removing the water pump. Thank you for the help.
Like Blwn31 said, not having a wiring diagram makes it hard to diagnose but on my aftermarket system the fuel pump gets it's signal from the ECU (through a relay) and it did the same thing once - running fine until I plugged in a hand held calibrator. It blew the in-line fuse to the ECU, dropping power to my coil, injectors and fuel pump. A new 3A fuse feeding the relay to the ECU brought it all back to life. I now carry a bag of fuses.
try switching relays for the fuel pump---there are 2 or 3 the same in the underhood fuse panel
Also try a differant key as the resistor in the key is matched to the computer and anti theft box
if the ecm doesn't receive a signal from the crankshaft sensor it will not trigger spark or injector pulse or fuel pump power so that's where I would start ......ted
Sounds like the Opti-spark distributor has failed. It is behind the water pump and the pump has to be removed to access. Here is a test...
.1 Check the operation of the optical distributor.
2. Disconnect the distributor 4-wire harness connector, then turn the ignition on. On the Powertrain Control Module (PCM) side, check for a 5-volt reference on both the low resolution (Red/Black) and high resolution (Purple/White) signal wires.
3. Verify that there is battery voltage on the Red wire and a ground on the Pink/Black.
4. Plug the connector back in. Check for good square patterns from both the low and high resolution circuits at idle or while cranking the engine. If a lab scope is not available, check for about 1 volt DC during cranking on the low resolution signal and about 2.5 volts DC during cranking on the high resolution signal.
5. If the signals are erratic or flat line 0 or 5 volts, check for bad, chafed wiring to the distributor. If all OK, replace the distributor
The opti spark distributor is bad about the bearing in the base to fail and actually melt the rotor or damage the module. Either way...it would be best to have it towed to a reputable shop and have it diagnosed and repaired there. Rough cost of the opti spark is 400.00 plus install
Btw...if the oil pressure sending unit fails it wil still have fuel pressure......You probably do not have injector pulse
Yes, Your LT1 PCM does control your Fuel Pump and your ignition if it is wired to do so. Some PCM wiring does not while others do. I would suggest that you get ahold of a scan tool for OBD1 and scan your PCM while turning it over. You can likely get an indication of what is going on. It could be something as simple as a fuse (I have three that control the PCM) or a ground for the PCM let go. Since you don't get your Fuel Pump activated while the switch is on but prior to the switch in the start position, these are the most likely things that can happen on your LT1.
Jerome
A simple check to isolate whether its fuel or spark is to spray some starting fluid, brake clean or even inflamablr hair spray into the intake--if it starts and then dies after the spray is burnt-===its fuel===if nothing, probably spark
and try a different key!!!!!!!!!!!!
simple check.....Koeo...does the check engine light come on? If no Start there..If i does, check for spark on two differant plugs. Should be a BRIGHT plug spark..IF not start at the opti spark. Check for Injector pulse..
The Opti is no easy change, it is buried under the water pump and you must remove Lots O Stuff to access it. It's a better part of the weekend to R & R it.
Keith
Thanks again. I'm learning the hard way. I did spray starting fluid into the intake hopeing to start the engine. I found that I did not have to drop the gas tank and replace the fuel pump. I tested the one I pulled out. The black wire is ground the gray wire is hot and the purple wire is the gas gage. My check engine light comes on whenever the key is in the run position and the engine is not running so that is no help. As I said my car is 75 miles from home so I have a limited amount of time to work on it. This past trip I started to remove the optical distributor. I did not have a harmonic balancer puller with me so the distributor is loose but not out. Like you said it is a real pain to remove. All the comments are appreciated. Hope this helps others.
I have NOT been able to remove the harmonic balancer so that I can replace the optical distributor. The puller that I have used to remove many chevy balancers does not work with the LT1 engine because the threads in the LT1 are 7/16 - 14 and previous models have 3/8 - 24 threads. I went to AutoZone and found their balancer puller will not accept the larger 7/16 bolts. I purchased a puller from Harbor Freight. The puller did not work because I could not keep the engine from rotating when I tightened the puller. I tried unsuccessfully to use a slide hammer to remove the balancer. I did remove the 7/16 -20 x 2 inch bolt and heavy washer from the crankshaft nose. It appears to me that this bolt does not do anything. Does this bolt hold anything or is its purpose to keep the threads clean??? Is the 1.25 keyed hole in the balancer a thru hole??? The reason I need to know this is that my next try will use a hydraulic puller that will push on the crankshaft nose with a 1.20 diameter rod. Thanks again for the help.
I've never worked on an LT1, other than helping my Son with minor things on his Camaro. But, if I remember right the harmonic balancer is a 2 piece bolt together unit. The balancer part can be removed without needing to use a puller to remove the hub part. The hub that stays on the crank snout isn't in the way = no puller needed. I could be wrong, like I say my son works on his car and I just assist if he needs an extra pair of hands now & then. Someone will chime in I'm sure & let us know if it actually is a 2 pc. unit.
the hub on the crank of an lt1 cannot be pulled with the normal dampner type pullers---the hub is a closed unit the bolt goes thru and it doesn't use the big thick washer of earlier stuff---
Dozer, have you Googled "LT1 Harmonic Balancer Removal"? There are a lot of discussions out there that give tips to the process, and explain what does and does not work. Most seem to point to a three claw puller for the pulley, then pulling against the loosened bolt or some smaller tool (one says a socket extension??) for the hub, if you need to pull the hub. Here's one - I cannot attest to it being right or wrong, just posting a link to get you started:
http://www.lateral-g.net/forums/showthread.php4?t=2770
This is what it looks like after you get the balancer off.
Dozer. Sorry I did not show the side view. It is a press on that does need a claw puller to get off. Should be easy with that!
You don't need to pull the balancer hub off to change the Opti, just pull the balancer/pully itself off. One other note on the LT1 balancer hub. It is not keyed like a normal SBC balancer is, it is just pressed on. You can't manually adjust the timing like on the old SBC due to once the relationship between the crank and cam is established via the timing chain, your timing is set. The Opti has a drive pin on it that indexes the timing off the camshaft. The computer does the rest. Are you gonna put a new seal for the Opti in the timing cover? Make sure before you install the Opti that the teflon seal and the Opti seal running surface are super clean. The teflon seals don't like any lube when installed, if there is they will leak.
Keith
I did not expect that. The picture says it all. Thank you. :oQuote:
Originally Posted by sfort
I have acted on all the good advise. The voltage tests show no voltage. The relays and fuses were replaced. The harmonic balancer was particularly dificult because of the rust from the salt used in the area in the winter. I had to make a hydraulic puller to remove the balancer as the pictures showed. I replaced the opti spark distributor, still no joy. I have just aquired a cpu from a suppositly runnable junk yard car. I will install it next time I am able to drive the 75 miles to where the car stopped. If this does not work I am going to pull the LT1 engine and replace it with an older engine. I am allowed to do this because the Chevy is a 1994 that does not require a computer scan to pass New York state inspection. Possibly I should have given up on this car, but I like older cars.
Dozer
Wow! This has been going on for almost seven months and it's still 75 miles from home with occasional trips to work on it? Have you considered towing it home, maybe on a two wheel dolly or getting a friend with a trailer & winch?
The only other cut off switch that can cause the ignition and the fuel to shut down completely is the fuel and ignition cut off switch that are installed incase of roll overs I had one go bad on me years ago and I was baffled for weeks too.....not certain if thats what it could be...but maybe worth looking into as well.
Dan
Just a note about ECU's. My Camaro(with an LT1) has a factory engine anti theft system, I believe it's called CAGS. If your car has it, the ECU reads the chip in the your ignition key. It looks for a set resistance (as burned into the computer) through the chip, if it doesn't match, the car will not start. I only mention this because you said you were going to replace the ECU. If you do replace the computer and your car has CAGS, get the chip out of the donor car ignition key and place it in your key.
Keith
Since the LT1 stopped last November I have replaced fuses, relays, ignition module, ignition coil, and distributor. The engine did NOT throw a code. I obtained a CPU from a donor vehicle. I was advised that I would need the chip from the ignition key of the donor vehicle. While swapping the CPU I noticed some green corrosion on one of the 128 wires on the CPU. I cut into the harness and found a section of wire that was discontinuous. I spliced a new piece of wire. The engine runs fine. One wire in 128 killed the entire engine. I find it interesting that I used my ignition key with a CPU from another car. I wonder if the anti theft chip really works. I have another GM vehicle that has an ignition key with a chip. I had a non chip key cut and it starts the car OK. Thanks for all the advise.
glad you got the problem solved.
the key works with the theft control modual, which also does doors, windows, power seat functions--ecu only needs signal from the tcm to run the fuel
can you tell me what pin number was corroded??and wire that was bad?
Yes that would be somthing to right down
Glad you fixed it.
Keith
The 4 harnesses to the ECU are color coded. It was the red wire in the black black harness. I didn't check the pin number. I didn't find the break with an ohmmeter. The wire was fat with green corrosion about 4 inches from the termination to the ECU