4x4jeepmanthing

I've started this thread to make sure I begin CORRECTLY diagnosing/ testing because right now ive reached my knowkedge limit.

Ok here's what I know,
99 auto just swapped in replacement engine, the jeep ran before this project.

I have a CEL, bluedriver shows P0122 i have not replaced the tps as of yet.The only test I've researched thus far said to do so while it's running, no go there.
I have fuel pressure in the rail
I have No spark at the ignition coil ( I believe I've tested the coil correctly) based on this threads test- https://www.cherokeeforum.com/f2/no-spark-1999-jeep-cherokee-227865/
though I'm not sure I had the multimeter on the right setting, a couple settings would get reading, a couple wouldn't. But if i moved the decimal over as the chart indicates it shows almost the max side on both.
.nss seems fine, reverse lights are on.
.the engine is turning over with the starter, just won't start


I have checked that the grounds:
.battery to body
.battery to block
.harness to rear of block
.harness to front of block
.strap to firewall
are clean and tight.

I need to know what to check next and what setting the meter should be on, it's a manual range.
diagnostics are something I know nothing about, please be clear on any advice, I surely won't pretend to know anything so instruction is exactly what I'm following here.

after all this work I just want to get my jeep running again.

thank you for any help guys

jordan96xj

Which of the following is true?

1. Cranks when you turn the key, but does not start (crank-no-start)
2. Does not crank when you turn the key (no-crank)

4x4jeepmanthing

#1
cranks, but does not start

gat

Were all of the connectors the same?
Find a starting wiring diagram and trace backwards from the coil.

jordan96xj

Locate the ASD fuse using the following post:

https://www.cherokeeforum.com/f2/99-...ostics-121730/

In Volts/DC mode on your meter. Place the black probe on battery negative. While someone cranks - place the red probe on either of the small test holes on the top of the fuse. You may also choose to use a test lamp for this. With the test lamp clipped to the battery negative, and the lamp probe/tip placed onto one of the fuse test holes (2 very small holes at the top of the fuse used for testing).

Which ever method you use, report back your findings.

4x4jeepmanthing

yes I kept all 99 parts

4x4jeepmanthing

we tried both methods. Test light remained on before and while trying to start, multimeter was at 12.47 and dropped to 10.8 once I tried starting.

I can hear and feel the ASD relay clicking when I key on power. Another discovery if it matters, the open door should beep with the key in, it doesn't beep unless I hold the key up in the tumbler a little. I believe it's done this a long time, I just noticed again.

DFlintstone

Was the CPS left bolted to the bell housing during the swap? If so, tough not to crunch that during a swap. Just a thought, I gather some failures there won't throw a code. With that shot I suppose the injectors wouldn't be firing ether. You said you swapped all parts but not from which year. I ask mainly because the torque plate is different for pre 91, fits fine but the notches the CPS uses are different.

4x4jeepmanthing

I did remove the cps before removing the engine, I read specifically to as to not damage it in the swap. Multimeter continuity doesn't tone on posts b,c. I believe it is still good?
I took all my original 99 parts, flex plate, ignition coil, distributor, everything stayed and bolted to the replacement block. Cap, rotor, plugs are new. It's getting fuel, I found a little dribbling from cylinder 4 onto my intake. Looks like new o rings are needed.

gat

If the coil isn't producing spark, then it either is defective or it isn't receiving voltage.

I'd think that a leaking injector would still leak when the injectors weren't being energized as long as the pump was pressurizing the rail. You might as well verify that the pressure is correct before and after cranking at the fuel rail. You should be able to unclip and pull off the connector from an injector to verify that the injectors are being energized.

If you can access a wiring diagram for the starting system, then that would be helpful to you. Haynes', Chilton, Mitchel, Factory Service Manuals, your local library would assist you.

jordan96xj

It's not that simple.

It must receive constant 12v power (with key on). But the circuit is completed (ground provided) by the PCM via a control circuit - which pulses to accomplish spark timing.

4x4jeepmanthing

so you want me to check the fuel rail next or what's my next step?
what did my test on the fuse tell you?

jordan96xj

We need to move to the ASD relay and ensure that during cranking that the PCM is providing ground to the control side of the relay. It will only do this if it is happy with what it knows about engine RPM, and crank/cam position (via the sensor signals it receives). If that ground is not being provided, we will know that the computer is not initiating ignition and we will have that a direction to start with. It will explain that there is no spark - because the PCM is not allowing it.

This can also be tested in a round-about way by probing the control side of the ignition coil connector. The control side is the wire that comes from the PCM and provides a pulsed ground that is responsible for generating spark via the coil based on the PCM's desired timing (cam/crank position). If that control signal is active, it means that the PCM is trying to allow spark to happen.

But both of the above will have to be happening for ignition to actually happen, because the positive side of the ignition coil (constant 12v) is going to come from the ASD relay. The ground/control for the ignition coil is going to come from the PCM. These make up the 2 wires you find on your ignition coil connector.

Do you have a wiring diagram for the sockets on your ASD relay? (because I don't want to advise you go probing around with circuits connected to the PCM unless we know which sockets to probe). I don't have a 99 Manual, and I don't want to assume that it is the same as my 96 (though it probably is).

4x4jeepmanthing

No sir I do not have a 99 service manual, but i will happily start scouring the internet for this relay diagram.

DFlintstone

You might check at cruiser54.com He has some manuals/info there, IDK about 99.So you can hold a something in the coil while it's cranking and nada....(that's how I finish diagnosing no spark)