UJSLOST

You got some information backing up the CPS will not fire the injectors? I have never seen a CPS control the injectors. Spark yes, but fuel no. Do you care to elaborate?

89cherokeelimited

I had a spark problem and the CPS fixed it but the fuel problem was other issues.
If the fuel pump is working properly have you checked the fuel rail make sure you are getting good pressure on the rail?

DFlintstone

Jeff, it's really easy for YOU to test your CPS. Just unplug it, and hook your meter to the leads on your lowest AC scale. (200V on mine). Then crank it with a good battery. .35 volts is really iffy. .5 and up is good. (find me or Cruiser54 for a bunch of cruiser's wrightups on Renix)

Post 90 non Renix sucks I guess. There is a resistance test nobody talks much about. I gather it might tell you if it's bad, but not if it's good. Wacky gauges, random stalling and no starts get mentioned. Napa premium (Echlin), or OEM Jeep are a good Idea since aftermarket can be dodgy.

A Renix will cut the ground to the ASD relay, killing spark and the pump if it doesn't have a good enough signal from the CPS....I think....if I have that right. Not sure if the OBDI does that or not.

OP, Id be real curious what my system voltage is doing if I where you. I guess these things really revolt without proper voltage. I'm such a bonehead I might hook a DVM to my cigarette lighter socket or something so I could watch what it's really doing, on the fly.

Jeffvador

I went out there and started it up and the battery meter is reading low. So I removed the battery's ground from the block and cleaned it reinstalled it. I started it up and still reads low. So I guess I need to barrow a volt meter and test my CPS I guess. Any other suggestions?

sgtskid

What does the voltage across the battery read while running? You should be able to place a multimeter across the terminals and watch with the engine running, it should read high 12's if it continues to drop your alternator is still not charging or has a bad ground.

stockli

Boats and Ho's

fishtaconc

Engine Start-Up Mode
This is an Open Loop mode. The following actions occur when the starter motor is engaged. The PCM
receives inputs from:
Battery voltage
Engine coolant temperature sensor
Crankshaft position sensor
Intake manifold air temperature sensor
Manifold absolute pressure (MAP) sensor
Throttle position sensor (TPS)
Starter motor relay
Camshaft position sensor signal
The PCM monitors the crankshaft position sensor. If the PCM does not receive a crankshaft position sensor
signal within 3 seconds of cranking the engine, it will shut down the fuel injection system.
The fuel pump is activated by the PCM through the fuel pump relay. Voltage is applied to the fuel injectors
with the ASD relay via the PCM. The PCM will then control the injection sequence and injector pulse
width by turning the ground circuit to each individual injector ON and OFF.
The PCM determines the proper ignition timing according to input received from the crankshaft position
sensor.

Although more than likely a no spark condition is more likely, and seen more often, it is possible.

Mendax13

i was gonna guess fuel pump or clogged fuel filter. although if its no spark... its probably not that.

UJSLOST

Ok, so after 3 seconds of not seeing a signal from the CPS the PCM will then shut down the fuel injectors . I see what your referring to here. But the injectors will pulse for atleast 3 seconds prior to the PCM shutting down the fuel injection. Which is plenty enough to start the engine. If there were infact a good signal from the CPS after those 3 seconds.


(Food for thought here, doesnt really have anything to do with the OP problem) Engine temperature sensor is going to tell the PCM how long to hold the pulse of the injector depending on engine temperature. Example: Cold engine, pulse is longer to provide more fuel to start a "cold" engine. Pulse is shorter because it doesnt need the excessive fuel to start a warm/hot engine. An engine that is hard to start when warm could have a bad coolant temperature sensor, which is telling the PCM the engine is cold when its not. Thus "flooding" the engine with fuel making it hard to start. (This is similar to how an electric choke on a carburetor works).

XJdryva

I'd check everything to do with the ground wires BOTH of them that come out of the battery terminal. Check them all the way to where they attach to the body and motor. I would also check the little ground strap on the driver's side of the engine near the firewall. I'd even check the hot wires on battery terminal as well

Big Blue xj

Ok so I still have no spark or fuel I replaced cps and still nothing I have clean all grounds it has brand new batt new Alternator ,new cps sensor , new tps sensor all relays and fuses are good I can bypass the fuel pump relay and I get fuel but doesn't work with relay in also still no fire

DFlintstone

Boy, what a choppy thread, (I didn't help!). I'm just trying to learn these things.
I know it's a new battery and all looks good. These things are not normal though. I really hope you have shiny lead inside that battery cable connector, as well as the posts. It can crank pretty lively and still not fire if it's not right. Mine just did that last week. I knew my old 08 battery's days where numbered, so I put in the new one I had waiting. Bingo. I then put the old Jeep battery in my truck with points, and it works fine, (for now).

Do you hear the pump when you turn on the key?
What brand of CPS did you install? Connector look good?
Grounds down by dipstick and rear of head have been cleaned?
Coil and ign, module have been separated, connectors cleaned?...Or maybe not an issue if your sure you have no fuel.

Wait..."""I can bypass the fuel pump relay and I get fuel but doesn't work with relay in also still no fire "".....The PCM grounding the ASD relay, and the ASD relay working are things I might want to check.


I think the ASD is grounded(by the PCM), providing power while you are cranking.

What codes now?