Hard Starting - 1990 Cherokee

Probably the anti-drainback valve in the fuel line leaking, allowing the gas that is supposed to stay in the fuel injector and fuel rail to drain all the way back down into the gas tank. The delay in starting is the time the fuel takes to get back up to the fuel injectors from the gas tank.

Jerry

Jeff Falkiner did pass the time by typing:

Fuel rail pressure. Fit a gauge to it and see if it stays about 32 psi and doesn't drop more than 4-5psi over a few hours. If it does you either have a leaking pressure regulator (front of the fuel rail), drainback valve (on the fuel pump), or a leaking fuel injector. further diagnosis isn't too hard but you need a set of hoses built for the job.

In the mean while you could try turning the key on, wait for the pump to cycle, then off, then on again. That cycles the pump and gets fuel and pressure back into the rail.

When my fuel pump was dying (91 XJ, 4.0) last year, it took longer and longer to start until one day when it just didn't. In my case, the regulator and drainback valve were fine. We replaced the pump and filter and everything is now tickity-boo.

Regards,

DAve

How complicated was this operation? You had to drop the gas tank right?

-Bill (remove "botizer" to reply via email)

They have a strange ignition system and seem to take forever to start first try of the day.

Ours got better maybe when we changed the gas filter, but it seems the CPS has to get a signal before the thing fires, so depending on where the flywheel is is an issue. I don't think the ones after 91 had this issue when they changed the computer system over.

I would go for the filter first.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Jeff Falk>

The XJ pump is in the front of the tank so you can pull it from under.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Wblane wrote:

Thanks for the help folks. We've got some work ahead of us.

Jeff

I would highly recommend you find another pre 91 Cherokee to compare cold start times before messing around. It sure 'seems' like a long start, but it could just be the normal 'long start'.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Jeff Falk>

8-10 seconds is a little too long. Maybe 3-4 seconds is what I consider normal even after sitting for weeks.

Might be a fuel problem. Have you buddy try to cycle the ign key on and off a few times and he should hear the fuel pump prime the system and then see if the starting time lessens.

Might be a CPS (crankshaft position sensor) problem. Have you buddy clean the CPS terminals at the harness plug and also tighten them. Apply some di-electric grease to the terminals too. See if that helps. ;-)

Of course the distributor may need indexing too since the history is unknown on this Jeep. Was a "tune-up" done? Plugs, cap, rotor, plug wires, filters, etc.?

later, dave AKA vwdoc1

88 XJ 4.0 auto

The service bulletin from Jeep about the CPS says to change the CPS AND wire the CPS connection directly to the computer, bypassing the large connecter directly above the brake booster.

While problems can come from a bad CPS, it is the high resistance at the CPS connection within the large plug and socket that should be resolved before replacing the CPS.

You should check the resistance within the CPS at varying temperatures (use a hair dryer or heat gun) as part of the troubleshooting if a hard start-no start-die out condition.

If the CPS seems OK, unplug the connector above the brake booster and clean the connections for the CPS.

and that kit the Dave in Columbus is talking about is only around $23 or so and it is the CPS too! My local dealer has never sold this kit, but I researched the price from galeana auto group.

FYI Regular CPS is around $50.

later, dave AKA vwdoc1

"Dave in Columbus" wrote

I've researched this for mine and I found that the crank sensor is often the problem. I replace it, and the problem went away.