fxct

Hi Folks. Thank you for reading this. I've been reading up on cranks-but-wont-start as it is afflicting my recently acquired 93 ZJ.

Yesterday it wouldn't start in the morning until the 5th or 6th try. When it started I noticed the VIC had reset, which I had not seen it do before. I did not trigger this particular reset by pulling the battery cable; this was "spontaneous".

Drove it around town, stopped twice, started it back up twice no problem. 3rd stop, it dies. Sparks, cranks, even tried to catch a couple times (promptly sputtering out) before just refusing to catch at all over like 20 tries. We whacked the tank hard several times; no dice. So, towed it back home.

This morning, it starts up immediately, no problems. Promptly drove it to Napa and picked up a few things.

Fuel pressure checks out. 35/40. I have a new fuel filter to install but since the pressure is okay I'm holding off on that for the moment.

At home where its quiet I can hear what I presume is the fuel pump priming. If it were not priming earlier I couldn't tell, it was too noisy.

This ZJ is at 150k miles, the CPS appears to be original and will get replaced, but I'm not getting any stalls while driving so I'm leaving that alone for the moment.

The CEL comes up with 12 and 55, and the 12 I don't know when it is from, because I *did* pull battery cables today while checking things out.

Spark is good; I have not tested all the points but since it is starting (at the moment) and running without a bad idle or anything I'm guessing that is not an issue.

The ignition coil has not been wet (its been hot and dry here of late) but I have not tested it specifically. It is on the list of potential things to replace, but I don't want to just start shotgunning parts in there quite yet...

Plugs, wires, distrib cap are all newish.

I don't wheel with this thing currently, though it is lifted, so its not being abused... its just a daily driver right now. Well it would be if it weren't doing this.

I'm wondering if the ASD (?) is being triggered, but I don't know much about how it works, or if I'd even get spark and crank if it were engaged. Once, the alarm went off, when it shouldn't have, it seemed, and I had to key the lock closed/open to disable it.

Thanks for reading this. This is my 1st Jeep; all I know is old (80's) Ford trucks otherwise.

Have the Chilton manual and basic tools, and am willing to get dirty / spent whatever it takes within reason to get this thing straight and reliable, before heading offroad and relying on it next winter.

fxct

Update: happened again later this afternoon. I'm not hearing the fuel pump prime every time I turn the key to "on" before turning it over. Seems like when I hear it prime, it starts. When I don't, it don't.

dave1123

Welcome to CF!

When it's running, try flexing the wire bundles to the PCM. If that makes the engine sputter or die, you've got poor connections on some of the pins where the cables go into it or bad solder joints on the terminal strips inside.

One other thing could be the capacitors taking time to charge up. Try turning on the key several times until you DO hear the pump, then try to start. Capacitors are temperature sensitive when they start to fail and can either stop functioning when hot, or take a while to charge when cold, or both. If you're good with electronics, these can be replaced and save buying a new PCM. Actually it won't be new with yours, it'll be refurbished.

With my wife's 96 Dodge Caravan, a code 12 was "start of test" and 55 was "end of test." Lately I've been told a code 12 is actually "battery disconnected within the last 50 starts." IDK either way.

The ASD relay has to engage to energize the ignition and fuel injectors. If things are not right, the PCM will allow it to drop out. The security system will also make it drop out.

Quick tutorial on the engine control system. When you start cranking the engine, the CPS sends a signal to the PCM telling it the crankshaft is turning. Then the PCM energizes the fuel pump relay and the ASD relay. The ASD relay energizes the ignition and fuel injector circuits. When the engine fires and starts to run, the PCM sends a preset mixture and ignition program to the engine. When the 02 sensor get up to temp, The PCM monitors throttle position, intake air temp and pressure (vacuum), rpm, vehicle speed, and sets mixture from the 02 sensor inputs. This is a quick and dirty explanation, but it should help you to understand what's going on.

fxct

> Try turning on the key several times until you DO hear the pump, then try to start. Capacitors are temperature sensitive when they start to fail and can either stop functioning when hot, or take a while to charge when cold, or both.

Seems to help, cycling the key positions a couple times and waiting to hear the primer go.

It has been more flakey when hot, than when cold. Read something yesterday about wrapping injectors to shield them from heat, particularly no. 3&4. Haven't done it yet, but seems like a very easy and cheap thing to try.

I will try wiggling those wires under the PCM and check for steady +5v on it otherwise, need to dig up my meter.

The positive battery cable(s) are a bit long in the tooth, I cleaned them up at the terminal yesterday and improved the contact, but will be replacing it shortly as well. The VIC did not reset overnight.

Called a shop and requested some time next week to get another pair of eyes on it, and to potentially do the CPS and fuel pump replacement if they turn out to need it... also have O2 and coil inbound, seems like things I should have on hand for a ZJ at this stage of life.

Thanks so much for the reply and particularly the ASD info!

dave1123

My 2000 WJ was recalled for a heat shield on the intake manifold. It turns out it's just an aluminum sandwich thing like an insulator blanket that just lays on top under the injectors. My WJ has cast iron exhaust headers and they soak up the heat. It can't cost that much, although with dealers anything is expensive.

fxct

Update on this: fuel pump replaced, problem gone for now. It never quit entirely but after ruling out many other possible causes, I replaced the pump and the pressure regulator. Before that I tested all the relays and fuses with a meter (all good except one relay had readings slightly off, replaced), then replaced the crankshaft sensor (readings were a little off there too), the throttle and o2 sensors (very old), cleaned the IAC, then wire brushed and cleaned all the terminals, grounds, relay pins and fuse pins, and it was still acting up.

The VIC is still occasionally resetting on rough surfaces, but that seems to be a loose wire somewhere under there, not causing any other issues ATM and tests aren't showing voltage drop.

Next up are differential service and a new t-case chain, then its on to the suspension...

dave1123

Yeah...Jeep=Just Empty Every Pocket! LOL! Just when you think you've got it good to go, something else tells you no.

Davehimself

sup all I have the same problem 93 zj i6 new batt, fuel pump, all the sensors too many to list but probly all of the m and not getting crank from starter
as well as running rough idk if I need new cat or 02 sens any more ideas ohh yea hradio stopped working as well as the dome lights and the vic wtf can some one help me understand this wiring catastrophy

dave1123

Now that's funny! My younger brother used to call that a "cats-after-me!" Anyway, being a 93, it's beyond my understanding as to how the electrical system is wired, but I suggest loose connections on the Body Control Module, if you even have one. Check with Cruiser54 to see if this is a Renix system or not. I know the early Cherokees (XJ) used a Renault-Bendix engine control and wiring connectors and grounds were very important for this system, not to say they aren't in all systems. cruiser54.com

I just went there and it seems the Renix ended in 90, but it's a good read anyway.

Davehimself

Well ive checked the grounds that i could find in the engine compartment im not sure what else to check or what that is you were takin about but ill do some research mine is a 93 grand Cherokee

Davehimself

I did get it started though neede an new starter relay i just bypassed it by pulling it out and used a jump wire however my dome lights and radio and vic still dont work unlesss i hold the bright lights back then all work....????? Wtf idk this is really getting me I now just have this as my daily I cubed my grand caravan soo i have to figure it out