Topic: 97 tj 2.5 cranks but no fire

[andrew383]

cranks just fine but i have no fire from the coil.
Things i have checked-
1) both crank and cam sensor's have been swapped out
2) coil has been swapped
3) wires from ecm to plugs for coil,crank and cam have been checked
4) ASD and FP relays have been switched around and both function
5) i have the 5v at the cam sensor
6) battery has been unplugged and ecm reset
7) when i remove the ASD relay the FP still kicks on when the key is turned on

Ive pretty much ran out of ideas here and need some help 

[neale_rs]

When my YJ was like that it turned out to be the computer itself.  I'm sure the TJ is different but on the YJ the main clue was that the check engine light was not coming on for a while when the key was tuned to RUN.

[andrew383]

it comes on for a few seconds then goes away when the key is turned on

[neale_rs]

Have you checked the codes from the ECM?  If nothing comes up I would get the computer checked to rule it out.

[andrew383]

i tried the way its told on JF with the key on/off deal but the light never flashed

[neale_rs]

I´m not sure if the 97 is like my 95 but on mine you have to cycle the key pretty fast to get it to work. I think on the TJs you get acual code numbers on the odometer readout instead of just flashes on the check engine light.

[jcsanders79]

I've never been able to get my 97' to code with the 3 turns of the ignition.  My sisters 01' worked everytime though?  I'd borrow/rent a code reader from an auto store.

[aw12345]

Well here are a few simple checks, do the injectors fire when you plug a noid light in? In other words with either a noid light or a small light bulb or test light does it flicket when you crank it? If so the coil is bad, if not see if you can get an rpm reading from the engine, either  from the tach or beg borrow or steal an OBD 2 scanner and see if it gives you cranking rpm  in the datastream, which would mean that the crancksensor and wiring to the ecm is good. Also when you crank it does it engage the ASD relais? Which would mean that the ecm does see an rpm reading from the crank sensor. If all that is happy look at the ignition module.

[andrew383]

Well here are a few simple checks, do the injectors fire when you plug a noid light in? In other words with either a noid light or a small light bulb or test light does it flicket when you crank it? If so the coil is bad, if not see if you can get an rpm reading from the engine, either  from the tach or beg borrow or steal an OBD 2 scanner and see if it gives you cranking rpm  in the datastream, which would mean that the crancksensor and wiring to the ecm is good. Also when you crank it does it engage the ASD relais? Which would mean that the ecm does see an rpm reading from the crank sensor. If all that is happy look at the ignition module.

did you see what all ive done so far?

[sharpxmen]

heard of this once and the distributor was out of sync (the cam signal was out of sync with the crank signal) - the ecu would err and not send issue a spark in that case, cant think of anything else out of the ordinary and since it seems that you did quite a bit of checks i won't go into the obvious ones.

[andrew383]

the dist has not been moved  at all,im really at a loss here as to what to do next 

[sharpxmen]

the dist has not been moved  at all,im really at a loss here as to what to do next 

i'll try and list what i can think of, you might have done all this but have a look:

one thing to check again is the voltage at the camshaft positon sensor - it is supposed to be 8v and not 5v (that's on my 95YJ). also check the voltage at the crank sensor as well (same there, 8v in my case).

I am assuming you did all the following but i'll list them anyway: check if the distributor is rotating, check 12v at the coil, test the coil, check 12v at injectors (all ASD related), check that you get ground while cranking at the injectors (or do the light bulb test like aw suggested), and since you said you have 5v at the cam sensor (or 8v?) that means you have power at the ECU. I would check the MAP sensor 5v and output (you should get 4.65v or so when you put the contact, and if you have a vacuum pump check that the voltage goes towards zero the more vacuum you apply). Also you might want to check the grounds as well at the sensors and that you have 12v ignition on pin 9 at the ecu (you should based on what you checked so far, white/yellow wire).

i would say if you gone thru all the above plus the ones you listed you could check the signals coming from the cam and crank with an oscilloscope and see if you get signals while cranking and to also check that your signals are in sync (it's a long shot as you mentioned that the distributor hasn't moved but you might want to look at it anyway if you have to oscilloscope connected - preferably one with 2 inputs/probes in that case).

I read this article a while ago and this image is relevant in this case: http://www.asashop.org/autoinc/feb99/img/fig4.gif with the explanation  below:
# Dst Sync (cam sensor) MUST be seen prior to crank signal.
# Crank signal is x amount of degrees after cam signal.
# Primary ignition signal is seen.
# Injector signal is turned on.
# Once in order, the PCM sees everyone is OK and allows the engine to run. Any other sequence and the PCM shuts down after two sparks!

and this is the link to the article http://www.asashop.org/autoinc/feb99/techtotech.htm - it is related to a 4.0L, but the idea is the same - just in case you run out of options.

[andrew383]

well im going to recheck all the voltages at the coil,crank,cam senors,and also at the injectors  then if all that checks out its new ecm time i guess :)

[que89yj]

Before you spend the big bucks for a new PCM you need to
1.check the faults.
2. check the voltage going into the coil?
3.There is a sync that needs to be run on the cam crank that you need a diagnostic tool to run.

[andrew383]

i'll try and list what i can think of, you might have done all this but have a look:

one thing to check again is the voltage at the camshaft positon sensor - it is supposed to be 8v and not 5v (that's on my 95YJ). also check the voltage at the crank sensor as well (same there, 8v in my case).

I am assuming you did all the following but i'll list them anyway: check if the distributor is rotating, check 12v at the coil, test the coil, check 12v at injectors (all ASD related), check that you get ground while cranking at the injectors (or do the light bulb test like aw suggested), and since you said you have 5v at the cam sensor (or 8v?) that means you have power at the ECU. I would check the MAP sensor 5v and output (you should get 4.65v or so when you put the contact, and if you have a vacuum pump check that the voltage goes towards zero the more vacuum you apply). Also you might want to check the grounds as well at the sensors and that you have 12v ignition on pin 9 at the ecu (you should based on what you checked so far, white/yellow wire).

i would say if you gone thru all the above plus the ones you listed you could check the signals coming from the cam and crank with an oscilloscope and see if you get signals while cranking and to also check that your signals are in sync (it's a long shot as you mentioned that the distributor hasn't moved but you might want to look at it anyway if you have to oscilloscope connected - preferably one with 2 inputs/probes in that case).

I read this article a while ago and this image is relevant in this case: http://www.asashop.org/autoinc/feb99/img/fig4.gif with the explanation  below:
# Dst Sync (cam sensor) MUST be seen prior to crank signal.
# Crank signal is x amount of degrees after cam signal.
# Primary ignition signal is seen.
# Injector signal is turned on.
# Once in order, the PCM sees everyone is OK and allows the engine to run. Any other sequence and the PCM shuts down after two sparks!

and this is the link to the article http://www.asashop.org/autoinc/feb99/techtotech.htm - it is related to a 4.0L, but the idea is the same - just in case you run out of options.

i shouldnt have 12v at the injectors should i?When the key is on there shouldnt be any voltage correct?
i did check out the wire(s) back to the ecm and there ok and the other wire was ground.Thge asd relay is clicking when the key is turned on and the fuelpump is also coming on.