Visited the site for help for a long time, finally posting. Long story short, I turned the key and the engine cranked and reluctantly started this morning. I turned it off and tried again: crank, no start. I've tried holding the gas pedal when cranking, and for a small second the engine responds before bogging down. The exhaust has a burnt carbon smell. I've tried on and off throughout the day, giving an hour+ in between tries in case it's flooded.


Brand new battery (nominal 12.5 V not cranking), new Idle Air Control, 30,000 miles on CPS, new fuel pump assembly, new head/valve cover/ exhaust/intake gaskets. I unplugged and replugged all sensors on the throttle body, unplugged and replugged CPS. Engine block is connected to ground. I pulled a spark plug wire (#1) and tested them with a screw driver against unpainted A/C compressor, and saw a spark. I think that rules out CPS, but I could very well be wrong.


I plan on getting some throttle body cleaner to spray in the throttle body and spark plugs tester. Any leads would be very appreciated as it's my daily driver, thanks!


1998 Cherokee RWD, 4.0L inline 6

 

Do you hear the fuel pump turn on when the key is turned on?

check fuel pump relay. Quick search will get you there.

 

I did. Also pressed the Schrader test valve both during and post-cranking to check pressure in the fuel rail, and there is fuel in there.

When I had the head and intake manifold off a couple months ago, the injectors had some gunk around them, but the area around the injectors was clean and free of any residue.

 

Did this start immediately after the head was done? If so, did the distributor get timed correctly and the plug wires in the right place? Refer to http://cruiser54.com/?p=68

 

Pressing the Schrader valve doesn't mean there's adequate fuel pressure to start. I've seen it many times. The fuel pump can put out 20 psi, which isn't enough to start. And you can't tell 20 psi from 55 psi by pushing the Schrader. Hook a gauge to it.

Unfortunately, having spark also doesn't eliminate the CPS. I've seen aftermarket CPS put out the wrong signal, which results in spark, but incorrectly timed spark. It having ran for 30k miles leads me to believe it wouldn't suddenly start putting out the wrong signal though, so it's an unlikely suspect.

 

Nope, it's been running fine for months. Would pulling a battery cable help to reset the computer, if that could be an issue?

 

1) very unlikely it would help...plus if you have a "brand new" battery you have just had the cables off;-)
2) any codes stored?
3) I don't know what "burnt carbon" smells like but with all that cranking I'm surprised you're not smelling fuel in the exhaust. As another suggested I would check the fuel pressure with a gauge. (I know you said it is a new fuel pump but.....) and take a look at the wiring harness/connectors feeding the injectors.

 

So... this morning I disconnected the battery for a few minutes and jiggled the connectors to the PCM (slight corrosion/oxidation on electrical connectors has always been an issue inside, usually fixed by plugging in and out a few times). I cleared any codes on accident and... it fired up. Sounded fine, went up to 3000 rpm on the interstate and it still ran great.

I don't want this to happen again, does this give any idea into what the root problem could be?

 

If jiggling the corroded connector fixed it you found your root problem-loose/corroded connectors. I suspect in this case the injectors weren't firing.

I would use contact cleaner and/or deoxit to get the contacts totally clean . (and remember the infamous dielectric grease is NOT intended to improve conductivity (it actually is an insulator) , it is only used to help seal whatever is supposed to waterproof the connector-like spark plug boots for example.