LS1 crank no start condition
LS1 crank no start condition Ok I've done just about everything I could possibly do or think of so I think its time to ask for suggestions. The cars a 1998 trans am with heads and a cam. The car has had heads and a cam for about 6 months now, I never had hardened pushrods I finally got around to installing them this weekend (side note I measured for the correct length during the install of the cam and had the car tuned with no misfires or any sort of damage from the pushrods being the incorrect length) after installing the pushrods I started the car and the car ran normally like it has been doing. I start cleaning up the tools with my friend who helped me and the car turns off. It wasn't an abrupt stall or anything with a bang or clang, just plain shut down. I go back in, the car cranks and does not start. Took out a plug, grounded it -no spark, looked over grounds on the back of the heads and they're fine. Took out the noid lights; no injector pulse. Took out the scan tool and no codes... coolant temperature sensor is reading correctly, crankshaft position sensor shows no RPMs while cranking... so im at a stand still here
and if you don't feel like reading all that heres a quick summary
changed pushrods (correct length)
No start condition checked already:
-coolant temp sensor
-checked ground wires
-grounded a plug found no spark condition
- used a noid light to find out no injector pulse
- no rpms being read during cranking on the scan tool
my questions for you guys:
Does the crankshaft position sensor control the injector pulse or does the PCM?
Should I rule out the Camshaft position sensor because it did not set a DTC?
any help would be appreciated
and if you don't feel like reading all that heres a quick summary
changed pushrods (correct length)
No start condition checked already:
-coolant temp sensor
-checked ground wires
-grounded a plug found no spark condition
- used a noid light to find out no injector pulse
- no rpms being read during cranking on the scan tool
my questions for you guys:
Does the crankshaft position sensor control the injector pulse or does the PCM?
Should I rule out the Camshaft position sensor because it did not set a DTC?
any help would be appreciated
this may not be you issue but I was having a similar issue, I could cycle the key a few times and it would start well it slowly got worse. so I did some reading on here to check the Crank Position sensor and the ignition relay under the hood. well I swapped out my ignition relay with the fan #2 relay and it fixed my problem.
this may not be you issue but I was having a similar issue, I could cycle the key a few times and it would start well it slowly got worse. so I did some reading on here to check the Crank Position sensor and the ignition relay under the hood. well I swapped out my ignition relay with the fan #2 relay and it fixed my problem.
Crank Sensor will give the signal to the PCM to send injector pulse and spark. So yes, sounds like you have an issue with the crank sensor, wiring, or PCM itself. The fact that you aren't seeing RPMs on the scan tool seems that it isn't receiving anything from the crank sensor.
Like mentioned above the most common cases of no start are:
Crank position sensor
Cam position sensor causes a no start condition however the crank sensor eventually takes over and you can start the car after cycling the key three times
Fuel pressure issue, pump going bad
Ignition relay
Coolant temp sensor being bad will cause the car to run like crap, or put the car into limp mode and dump fuel assuming the engine is cold
Crank position sensor
Cam position sensor causes a no start condition however the crank sensor eventually takes over and you can start the car after cycling the key three times
Fuel pressure issue, pump going bad
Ignition relay
Coolant temp sensor being bad will cause the car to run like crap, or put the car into limp mode and dump fuel assuming the engine is cold
Trending Topics
Update for today...changed the crankshaft position sensor. Same condition. Wires to the sensor are ok not frayed kinked etc also have power at the harness. For piece of mind pulled a valve cover to see if anything can give me a hint there...nothing everything was moving freely like it should..now I'm stumped I really don't know what to do now
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
Topdon ONE vs. Artidiag 800 BT2: Which is the Diagnostic Tablet For You?
Pouria Savadkouei
Gas Monkey Built a 6-Wheel Ferrari Testarossa With a Corvette LT4 Engine
Verdad Gallardo
7 Most Reliable High-Performance Engines GM Has Ever Built
Verdad Gallardo
Amazing '71 Camaro Restomod Is Modern Muscle Car Under the Skin
Verdad Gallardo
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
See what code the pcm is storing. Then follow the tree for the code and it will lead you to the problem you'll need a scanner and a voltmeter.
There is also a trouble tree for no spark that will walk you through the steps it's the only way to reliably fix it or find the problem without throwing parts at it and wasting a bunch of time.
There is also a trouble tree for no spark that will walk you through the steps it's the only way to reliably fix it or find the problem without throwing parts at it and wasting a bunch of time.
Update for today....followed the diagnosis flow chart and it lead me to the pcm checked the pin outs everything checks out ok. I have power and grounds everywhere there needs to be. All work leads to a faulty pcm... for ***** and giggles on my last attempt I tried cranking one last time before going in I noticed that the car is not building oil pressure while cranking.. is this because I removed the pcm? Before this I was getting normal pressure and now it wont move on the dash gauge. I'm afraid this just took a turn for the worse.
Update for today....followed the diagnosis flow chart and it lead me to the pcm checked the pin outs everything checks out ok. I have power and grounds everywhere there needs to be. All work leads to a faulty pcm... for ***** and giggles on my last attempt I tried cranking one last time before going in I noticed that the car is not building oil pressure while cranking.. is this because I removed the pcm? Before this I was getting normal pressure and now it wont move on the dash gauge. I'm afraid this just took a turn for the worse.
If you have ruled out the sensors I would go ahead and get a different PCM. Make sure your connections to the ignition coils are all plugged in. You will need a 98 PCM only
so i got new pcm and installed it today same service number and everything on it would it be necessary to program it before the car would run or should it start? it didnt start and i wanted to make sure before i triple check the grounds on the heads again
Teching In
Joined: Aug 2016
Posts: 12
Likes: 0
Did you solve your problem? Im having the exact issue and i did the exact steps you did. Injectors getting pulse but i think its still something with the crank position sensor.
TECH Addict
Joined: Mar 2013
Posts: 2,628
Likes: 30
Next would be do you have fuel pressure and spark? PCM works like this....you turn key and engine starts to spin.....PCM gets CPS signal ...turns on spark ....then turns on fuel. If its not starting and the injectors are pulsing its sure bet you don't have fuel or fuel pressure. If the injectors are pulsing and the engine is not starting AND you have fuel pressure shortly the crank case and exhaust will reek of fuel. Its been a while since I seen the schematic's but you could swap the ignition and fuel pump relays with other relays to see if it starts. A bad ignition relay or fuel pump relay will cause it not to start if it cranks.
Last edited by RockinWs6; Nov 5, 2016 at 11:14 PM.
Check fuel pressure at the rail at the test port. If you have pressure, pull an injector and see if it's spraying. If it is, move to spark. Plug in a spark test lead and check.
Do the easy stuff first. Fuel. Spark. Then start backtracking to the wiring harness or PCM or fuel pump if one or both of those are not present.
And as others have said. You can unplug the cam sensor and it'll still fire. The Crank sensor is the one that will cause you issues.
One other question - is it turning over and just not firing?
Do the easy stuff first. Fuel. Spark. Then start backtracking to the wiring harness or PCM or fuel pump if one or both of those are not present.
And as others have said. You can unplug the cam sensor and it'll still fire. The Crank sensor is the one that will cause you issues.
One other question - is it turning over and just not firing?
Teching In
Joined: Aug 2016
Posts: 12
Likes: 0
Check fuel pressure at the rail at the test port. If you have pressure, pull an injector and see if it's spraying. If it is, move to spark. Plug in a spark test lead and check.
Do the easy stuff first. Fuel. Spark. Then start backtracking to the wiring harness or PCM or fuel pump if one or both of those are not present.
And as others have said. You can unplug the cam sensor and it'll still fire. The Crank sensor is the one that will cause you issues.
One other question - is it turning over and just not firing?
Do the easy stuff first. Fuel. Spark. Then start backtracking to the wiring harness or PCM or fuel pump if one or both of those are not present.
And as others have said. You can unplug the cam sensor and it'll still fire. The Crank sensor is the one that will cause you issues.
One other question - is it turning over and just not firing?
Teching In
Joined: Aug 2016
Posts: 12
Likes: 0
Next would be do you have fuel pressure and spark? PCM works like this....you turn key and engine starts to spin.....PCM gets CPS signal ...turns on spark ....then turns on fuel. If its not starting and the injectors are pulsing its sure bet you don't have fuel or fuel pressure. If the injectors are pulsing and the engine is not starting AND you have fuel pressure shortly the crank case and exhaust will reek of fuel. Its been a while since I seen the schematic's but you could swap the ignition and fuel pump relays with other relays to see if it starts. A bad ignition relay or fuel pump relay will cause it not to start if it cranks.