89 4.0 Running great until sudden no start

[ttanton]

Hey guys,

 

Heavy lurker here. I'm a relatively new owner (about 1 year). Been working through Cruisers mostly renix updates, driving the truck 2 - 3 times a week. It's been mostly solid for me minus a fuel pump replacement about 6 months ago.

 

The problem: Today while running errands, I was on my 3rd or 4th stop when the truck just straight up wouldn't start. I have never had trouble starting the truck throughout the last 12 months. But today after starting several times just fine along the way, it wasn't even thinking about it. Strong crank, smells relatively rich after cranking a while, but seems like no fire. The electrical in this rig is not the best, whacky stuff from PO etc, but again, it has generally been trustworthy and I've refreshed most of the grounds etc. It's (not) driving me nuts how it just went from 100% fine to 0% fine so quickly 

 

It's currently stranded at the local gas station. I'm going to head back tomorrow morning to play with it for a few hours before resorting to towing measures. My plan so far is the following:
 

1. Check for spark
2. Check for fuel pump power/fuel pressure (pump replaced ~ 6months ago, priming has been silent since then, so hard to hear, but when cranking and no start, exhaust smells rich)
3. Check CPS

 

I'm all ears if anyone has ideas for relatively simple gas station diagnostics. I installed NickInTimes REM too if that can help. Not much else to note. Blower motor fuse blew a few days ago, and I played around a little in the fuse box below the driver to address that (all sorts of jumps and whacky stuff down there, but again nothing changed recently since it's been running well).

Thanks in advance for any advice. I'll be browsing through existing topics heavily as well in case I can draw anything there. Cheers.

[fiatslug87]

Have you tried disconnecting and reconnecting the CPS? Sometimes that works.

 

Also put some of the MJ’s details in your signature: year/engine/trans, etc.

[Ωhm]

Look at the vacuum hose between the Fuel Pressure Regulator (FPR) and intake manifold for fuel. Leaky FPR.

[ttanton]

I’m going to try both of these tomorrow morning when I head over there - I’ll check the cps connector and vacuum hose to the FPR. Thank you both

[Alan C]

Does it fire at all? I had a problem in that mine would want to start but not actually run. It turned out the wire to the ballast resistor (on the driver's side inner panel) was corroded. Doesn't sound quite like your problem, but checking those wires would not hurt.

 

https://www.youtube.com/watch?v=01JeJPjJRDs

 

Good luck!

 

[ttanton]

@Alan C No, it doesn't fire at all - dead as a doornail. Thanks for the reply.

[cruiser54]

All good advice so far. Take a peek at the throttle body to MAP sensor tubing while you're at it and make sure your CPS wires aren't melted on the exhaust. 

 

 

[ttanton]

Headed over right now. Will be checking all vacuum tubing from the intake manifold to map & fuel pressure reg, and check on the cps wiring and sensor tip if I can get to it. Thanks all - will follow up once I know more this morning

[ttanton]

Confirmed no spark at the plugs. trying to work my way backwards and up the line to see what’s failed I guess. 

[ttanton]

Testing the ignition coil. I’m only getting about 0.5 ohm resistance between positive and negative terminals. Chitons says I should be .95 - 1.2. Not sure if that’s far enough off to be a problem though. It’s a spectra ignition coil, looks relatively new, replaced by PO.

[ttanton]

I am getting infinite resistance between positive terminal and  high voltage terminal or case. So secondary resistance seems okay 

[Ωhm]

Disconnect C213. Check for Battery Voltage (B+) on C213_A with KEY ON and during ENGINE CRANK. C213_B is the GROUND leg for the Ignition Control Module (ICM).

 

 

[ttanton]

I put a plug in the wire from the ignition coil and cranked and did spark from there. Going to look at what ohm shared above too though 

[ttanton]

Got it turn over! Spark again at the plugs. dang SOB.

 

My guess is, the in high voltage terminal on the distributor cap didn’t have a good connection. It had some corrosion on it. Me plugging and unplugging and wiggling was enough to reconnect everything. That or the terminals from the wiring harness to the ignition coils. Those were pretty rough too, I brushed and bent them back for better contact with the coil block. 

[ttanton]

Thank you all for the quick replies and suggestions. Hope everyone has a great new year! Cheers.

[cruiser54]

excellent!! Always refresh connections before replacing components. 

 

That said, your Jeep is due for plugs, wires, cap and rotor every 30,000 miles.