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4.0 won't start

C

cykaaro

NAXJA Forum User
Location
ontario, canada
We're trying to get a friends '93 ZJ started but running out of what to try. I know it's not an XJ, but has the 4.0 engine so figured someone may have an idea.

We can get it to turn over, has spark, and fuel, but it won't catch. We did get it to spit out a code '41' on it though. We also checked the voltage to the CPS which is 8v which it should be.

Anyone have any ideas at all???

TIA
 
cykaaro said:
We're trying to get a friends '93 ZJ started but running out of what to try. I know it's not an XJ, but has the 4.0 engine so figured someone may have an idea.

We can get it to turn over, has spark, and fuel, but it won't catch. We did get it to spit out a code '41' on it though. We also checked the voltage to the CPS which is 8v which it should be.

Anyone have any ideas at all???

TIA
Click to expand...

If it has spark and fuel it should run. Usually it's either the crank sensor, fuel pump, or coil.


Mike R
 
cykaaro said:
Was thinking CPS as well.
As for coil, could that be, even though it's getting spark?
Click to expand...
With a bad CPS you will not have spark or fuel. Make sure you have at least an inch of blue spark, a 1/2" of yellow spark is not good.
 
Just pull a plug out and check for spark with it grounded to the block. If the coil were bad you could still get spark but a weak one. They usually crack and start arcing at the coil. One thing a lot of people don't realize is you can flood a injected engine by giving it gas as you are cranking. There is a clear flood feature on most DCX vehicles. Basically it you hold it wide open throttle while cranking the engine controller will shut off the injectors. I'd pull the plugs and see if they are wet or carboned up. I wouldn't rule out basic maintanance either (just had a XJ with 67K on it and had original plugs/wires/etc... the coil wire came apart and three of the posts on the dist cap were corroded bad). Plugs should be done every 30K and cap/rotor/wires every 60K.


Mike R
 
langer1 said:
With a bad CPS you will not have spark or fuel. Make sure you have at least an inch of blue spark, a 1/2" of yellow spark is not good.
Click to expand...

I've read conflicting info on this...Can anyone confirm if you get spark with a bad CPS? I thought that spark and fuel, but no start, pointed toward CPS.

TIA, my 96 just died at a traffic light today. Stuck at work for now, but trying to get an idea of wher to go.

Steve
 
SteveT said:
I've read conflicting info on this...Can anyone confirm if you get spark with a bad CPS? I thought that spark and fuel, but no start, pointed toward CPS.

TIA, my 96 just died at a traffic light today. Stuck at work for now, but trying to get an idea of wher to go.

Steve
Click to expand...

The crank sensor tells the engine when to fire the coil (and the distributor rotates to the correct cylinder) and whether or not to keep the fuel pump running (engine RPM's).


Mike R
 
Here's another little trick. Roll up all the windows, and lock, then unlock the door with the key. The factory ATS system gets tripped whenever the battery goes dead, a door is unlocked from inside (you wouldn't believe how many calls I get from people who opened their door lock through an open window, then it wouldn't start!) or the vehicle is towed.
I tried to defeat this junk with the '93 ZJ I parted so I could put the EFI in my '84 J10. It didn't want to play that game! Door locks were too mangled to reuse.
 
carnuck said:
Here's another little trick. Roll up all the windows, and lock, then unlock the door with the key. The factory ATS system gets tripped whenever the battery goes dead, a door is unlocked from inside (you wouldn't believe how many calls I get from people who opened their door lock through an open window, then it wouldn't start!) or the vehicle is towed.
I tried to defeat this junk with the '93 ZJ I parted so I could put the EFI in my '84 J10. It didn't want to play that game! Door locks were too mangled to reuse.
Click to expand...


Windows don't matter, you can use the key in either front door or rear hatch, Jeep calls it VTSS (Vehicle Theft Security System) and if it's tripped it will start then die along with flashing headlamps and security light on the dash (triggered by battery voltage dropping below 8-9V or battery disconnect otherwise the horn will honk also). It can be removed only by removing the VTSS module and replacing the engine controller.


Mike R
 
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Did you ever figure this out I have the same problem. Spark and Fuel but wont start. Mine wont even start when you spray starter fluid in the TB. Still trying to figure it out.
 
Just out of curiosity did either of you two that are having issue, check the timing with a timing gun? If you have fuel and spark then it is not the CPS. The only two things are a week coil or a timing issue. The far reacher would be a TPS being stuck and flooding the vehicle. Pull a plug right after cranking the engine. Is the plug wet or dripping? wet means normal fuel dripping means to much and it might be the TBS sending a wrong signal. Also check the rotor button if it is slightly corroded it can stop a spark or weeken it severly. Cracked rotor caps are also an issue in cold climates(don't get me started on that one). But check the timing make sure it is sparking at the right time, or else fuel and spark wont matter much.
 
Last edited:
I've noticed a lot of you guys overlook the cam position sensor. It's always crank sensor this and crank sensor that. Beneath the distributor cap is the cam position sensor. The crank sensor merely sends an RPM signal to the controller to tell it to give power to the injectors and coil. The cam sensor tells the computer when to actually fire the injectors.

Try a cam sensor. Check the distributor shaft for play side to side. And make sure the distributor is timed correctly. If it tries to actually fire up now and then, it might be firing the wrong injector.
 
db209_2000 said:
I've noticed a lot of you guys overlook the cam position sensor. It's always crank sensor this and crank sensor that. Beneath the distributor cap is the cam position sensor. The crank sensor merely sends an RPM signal to the controller to tell it to give power to the injectors and coil. The cam sensor tells the computer when to actually fire the injectors.

Try a cam sensor. Check the distributor shaft for play side to side. And make sure the distributor is timed correctly. If it tries to actually fire up now and then, it might be firing the wrong injector.
Click to expand...


This is why I told them to check the timing. I'm trying to stop them from buying more parts that is not needed. If the timing is of then we can go from there.
 
Mine will Faintly try to start If I floor it and crank for like 10 secs, But will not start.

If the Cam position sensor goes bad wont it usalyy just stop firing the injectors? Mine fire for sure, and I get spark

But it does sound like its turning over weird. I hope its the CPS!!
 
Last edited:
Elfwizard1975 said:
Mine will Faintly try to start If I floor it and crank for like 10 secs, But will not start.

If the Cam position sensor goes bad wont it usalyy just stop firing the injectors? Mine fire for sure, and I get spark

But it does sound like its turning over weird. I hope its the CPS!!
Click to expand...


do not waste your money on the CPS(crankshaft position sensor) that's not it. It sounds more like a timing issue. The CPS either works or it doesn't work. If it doesn't work you do not get fuel or spark because a relay is turned off stoping the spark and the fuel injectors. Look at my previous posts. If your timing os out and you can tell from just cranking it then you can look at the cam shaft position sensor(CSPS). I'm also leaning twards the TPS(throttle position sensor) if you unplug that the comp should defualt and the vehicle should run, crappy but run.
 
Last edited:
Never did find out the outcome of it, but weirdly had the same damn thing happen to me. Turns out that the timing chain slipped or such. It was of course like a lot of things on mine, the original one, so had the gears and chain replaced. The chain had a slack of 1 1/2" when it should be 10mm!!

Of course asked a lot of questions. My mechanic told me that if you get spark, then the CPS is ok. Ended up changing the rotor and dist. cap as it needed to be done, as well as the spark plugs. With fiddling with the cap, we could almost get it to go, but just not quite. Also found one of my injectors was leaking too. Hopefully she'll hold together now for me for a while longer until I can get the engine rebuilt.
 
cykaaro said:
Thanks, will pass along..........

What does getting a yellow spark signify?
Click to expand...

A good spark will be blue...yellow is sign of a bad coil...been there done that bout 2 wks ago.....
 
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