jbarker

Hi folks:
New to this forum. I have a '97 Cherokee Sport 4WD stick 4.0 liter that I bought new. It has 270k on it and has been a wonderful vehicle. Runs like a top. Couple weeks ago it began getting a little hard to start. Got progressively worse. Now it must be cranked for several minutes before it starts, then takes a little acc fluttering to keep it going. However, once it runs for a little it runs smooth. No misfiring at all.

Pulled all plugs - look great, no carbon, all uniform tan, cleaned and gapped and re-installed. There is pressure on the fuel rail at the test port (have not measured yet). Gas is fresh (car gets driven every day) and has drygas added. Haven't checked compression or anything else yet because I can't understand why it runs so well!

One odd thing, the temp gage starts at over 100 - did not use to do this, then climbs as the engine warms. I'm wondering if I've got a bad temp sending unit that is fooling the ECM into thinking the engine is warm before it actually is. Anyone know exactly where the sending unit that the ECM reads is on this vehicle?

Any help is much appreciated.

joe bob

Im not sure what the temp. has to do with it but with the high miles I would try seafoam to help clean up the engine.seafoam= magic in a bottle.

Abovetimberline

I would do a compression check first and see how healthy the motor is,I had a couple of cylinders at 60lbs and it ran fine once it was warmed up.
I would also check the fuel pressure with a guage if possible.
And check cps,I would think the cps would be an issue at all times but it is worth looking at.
It sounds like a fuel issue it sounds like the fuel is just taking along time to charge the rail.
Othere things to look at are the tps and iac,

jeepgeek2002

buy the fuel pressure gauge.. if its under 39lbs.. its the fuel pump..
mine ran like a champ, then one day..long long crank. next day long longer crank.. then eventually i had to floor it for it to stay running..

OBD1 showed MAP sensor failure..even though it was a Fuel pump.

Mark

SeriousOffroad

#39psi? Try again....the op has a 97.
Hint:
You're off by 10 psi.

Do a leak down test. Even money says it's your checkvalve in the pump assy. No need to replace the pump, just add an aftermarket check valve.

jbarker

My thinking on the temp sensor was if the computer thought the engine was warm when it was actually stone cold, the fuel mixture & amount might be off. Anyway I replaced the sensor, gauge now goes to low pin but Jeep still hard to start - although a little better than before maybe. It cranks fine just no fire.

Note - it's a temp related problem because once it's a little warm, restart is no prob.

So once it stops snowing I'm going to check compression, cylinder leak-down and fuel pressure. BTW Chilton has idle fuel pressure spec = 31 psi and sez the fuel return valve on a '97 is built-in to the regulator which is on the tank. I might note I REALLY don't want to drop a tank outside in winter in NH.

Thanks for all the help & stay tuned.
JB

jbarker

One piece of info I failed to note - no check engine light. I don't have an OBD-II scanner but I assume no codes if no light - is this correct?

Abovetimberline

Cgeck your light bulb and make sure it is good.

jcstaten

Have you tried cleaning your battery terminals and post. Mine did the same thing. They looked fine but they actually needed cleaned because there was a thin layer of buildup that was causing a bad conection.

ET JEEP

The CEL should turn on when you turn the key to on. It will stay lit for a few seconds then it should go out. This is a system check.

Try this, turn your key to on and let it stay on for a few minutes before trying to start the engine. After 3-5 minutes try to start the engine and see if you notice it starting faster than it has been starting. Also, see if the check engine light blinks or turns on during this period.

jbarker

OK, more data (love that stuff).
CEL is OK, lights up, goes out after a few secs, does not come back on.
Fuel pressure gage: 44 psi idling.
Interesting thing: With gage on port and zeroed, turn key on, gage goes to 44 psi (it has a hold feature), hit the button and it drops to zero (with key still on). Seems like the pump comes on for a second to precharge the fuel system - makes sense to me. Can anyone confirm this feature?

The only anomoly was some pressure gage needle fluctuation - fast bounce - during idle. First test was not there, second it was. I was holding the gage head in my hand so not engine vibe. Still max hold feature was solid at 44 psi after I turned off the engine.

So, ever since I replaced that temp sensor she's been starting up pretty good. I'll polish up those battery posts JIC but it cranks fast. Still, it has not gotten real cold of late but the forecast is it will in the next couple of days. I'll keep you posted.

Thanks for all the input.
JB

jbarker

One more thing. Chilton talks about re-measuring fuel pressure "with the pressure regulator vacuum line disconnected". My regulator is mounted on the tank. Anyone know where the other end of that vacuum line ends up? Gotta be somewhere on the IM but I'm not sure where - there are a few.
Thanks,
JB

jbarker

Frank - pressure on the rail drops to zero in a few seconds after engine is killed. In my mind this would be consistent with a tank-mounted regulator - no pressure and it bleeds psi back in to the tank. What do you think?

Since it holds 44 psi idling it would seem that even if the check valve is leaking, it's not enough to overcome the pump capabilities.

Thoughts?

SeriousOffroad

It's a bad checkvalve in the pump assembly. Get an inline checkvalve and mount as close to the tank as possible.

cherokeeguy

Seems like the pump comes on for a second to precharge the fuel system - makes sense to me. Can anyone confirm this feature?

Yup this is normal!