95 YJ no spark

[TrailsvsRoad]

Hey everyone, looking for some help tracking down a no‑spark issue on my ’95 YJ (4.0L, manual). I’ve gone through the basics but I’m still missing something.

Symptoms
- Engine cranks strong but will not start
- No spark coming out of the ignition coil
- 12V is present going into the ignition coil
- Fuel pump primes and I have fuel pressure at key‑ON
- Dash lights come on normally (Check Engine, Brake, etc.)
- Tachometer does not move during cranking
- No spark at coil → distributor

What I’ve Tested So Far (Voltage‑Only Tests)
I’m working with a multimeter that can only read DC voltage, no resistance/ohms mode, so I followed a voltage‑based diagnostic sequence.

1. Ignition Coil Power
- Coil positive has ~12V with key ON
- Coil positive has ~12V during crank
→ So ASD relay is powering the coil

2. Coil Negative (PCM Trigger)
- Tested coil negative by putting meter black lead on battery positive and red lead on coil negative
- During crank, the voltage does NOT pulse
→ PCM is not grounding the coil

3. ASD Relay Output
- ASD output has 12V at key ON
- ASD output stays at 12V during crank
→ ASD is not dropping out

4. CPS (Indirect Tests)
- Tachometer does not move at all during crank
- PCM power stays at 12V during crank
→ Looks like PCM may not be receiving a crank signal

5. Injector Pulse
- No injector pulse during crank
→ Points toward CPS or PCM not triggering ignition/injection

What I Think It Might Be
Based on the tests:
- CPS signal not reaching PCM (even if sensor is new)
- Distributor pickup (cam sensor) not providing sync
- PCM coil driver failure (common on ’94–’95 YJs)

What I’m Looking For
- Does this test sequence point more strongly to CPS wiring vs. distributor pickup vs. PCM failure
- Any additional voltage‑only tests I can run
- Known weak points in the ’95 YJ ignition wiring I should inspect
- Confirmation that PCM coil driver failure matches these symptoms

Any help is appreciated — trying to narrow this down before throwing parts at it.

Thanks in advance.

 

[mea0033]

Hallo, vielleicht kann ich dir helfen. Nach einer längeren Standzeit aufgrund einer Generalüberholung hatte ich mit meinem 89er 2,5-Liter-Motor ebenfalls massive Startprobleme und bin folgendermaßen vorgegangen:
– Alle Sicherungen geprüft „waren in Ordnung“
– Relais geprüft „waren in Ordnung“
– Zündfunken an den einzelnen Zündkerzen geprüft „Zündfunke war vorhanden, aber der Motor sprang trotzdem nicht an“
– Zündreihefolge geprüft „Ich hatte die Steuerkette gewechselt und vermutete, dass die Steuerzeiten nicht stimmten, war ok"
– Kurbelwellenpositionssensor geprüft „war in Ordnung“ Widerstandsmessung siehe

– Ich vermutete auch ein defektes Steuergerät und habe es dann erfolgreich mit einer Prüflampe "Noid Light" getestet.
– In meinem Fall war es die Einspritzdüse „Ich habe nur eine zentrale Einspritzdüse“.

Meine Empfehlung:

1. Bei deiner Fehlersuche solltest du zuerst die Ursache für den fehlenden Zündfunken untersuchen → Kurbelwellenpositionssensor! Könnte es ein Timing Problem mit der Zündung sein? Das hattest du ja schon erwähnt.
2. Wenn der Kurbelwellenpositionssensor tatsächlich in Ordnung ist, sollte man zusätzlich eine Prüflampe verwenden. Leuchtet die Lampe nicht, liegt kein Einspritzimpuls vor (siehe
   ).

Grüße aus Frankreich

 

[TrailsvsRoad]

Danke.

Everything you stated I've tested. The pulse that is supposed to be coming off of the PCM ground is constant and does not pulse. I have checked it at the PCM at the injectors at the CPS and the coil.

 

[Chris]

If it were me I'd consider sending the PCM to Mark (wranglerfix.com) to have him test it for you and rule it out.

 

[TrailsvsRoad]

If it were me I'd consider sending the PCM to Mark (wranglerfix.com) to have him test it for you and rule it out.

I sent it off today to someone a bit more local to do the same. If they state they can't fix it will for sure check them out.

 

[lee si hwa]

캠센서+크랭크각센서 교환----PCM----인젝터.점화 영향있습니다...