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hard to start not a starter issue

GordoSmasho

Nevada Raisins
NAXJA Member
So back story is I got a 97 two door 4x4 4.0 Aw4 for free. Obviously had some issues. I rebuilt the engine. New head and the things I will detail below. Issue is it takes a long time cranking to start. It has a new battery and its cracking at normal speed. I heard about the check valve in the tank so I tried a few times cycling the key several times before starting and no difference. It takes a good 5to 7 seconds of cracking to start. Fluctuating the gas doesn't seem to affect it. Once it starts it runs like a gem. Smooth as can be with great throttle responce. There is a slight dip in power through the middle rpm range 2500 to 4000 but it is still getting out of its own way. I'm thinking cps anything else I should be checking. It just passed smog but there was a spike in the nox at the 25mph vs 15mph. From 7 to 590 all other values were well within parameters. Also looking for some input on that.

List of things replaced within 500 miles.

Head from a 98 good condition replaced valve seals
One piston from the same 98 #1 cylinder
New piston rings
New main and rod bearings
New timing set
New radiator
New battery
Plugs(champions) wires cap and rotor
Air filter
All shift solenoid
Thermostat
Radiator cap
Master gasket kit

Any suggestions or direction welcome.
Thanks for your time.
 
Since this is relatively recent rebuild with new rings, etc, the engine is not broken-in yet. A lot of friction is generated in a rebuilt tight engine and you'll notice it when starting. Likewise, the engine will run a little warmer for awhile until the rings seat properly and parts wear-in. As long as the engine starts and runs normally, oil pressure is OK, I wouldn't worry about it until you get some significant miles on it.

One thing I do with rebuilt engines to fire them up and run for an hour at about 2000 RPM. That throws oil on the cylinder walls for lubrication and cooling, breaks-in the camshaft etc. After checking for oil leaks, etc., I take it out on the road and accelerate at about 75% throttle up to 60 mph and then let it coast down to 20 or 30 mph. The acceleration forces the rings against the cylinder walls to seat them. The coast down oil get on the cylinder walls to lube and cool them down. I repeat this acceleration and coast for about 6-12 times.

Best regards,

CJR
 
In my view, a few hundred miles does not break-in an engine properly. A lot has to do with the type piston rings used (some types take longer to seat than others), if the crankshaft was reground and not binding in bearings, whether the crank and cam bearings were align-bored, tight fitting valve stems which loads the camshaft and in turn loads the engine, cam advance, etc.. Accelerations at 75% throttle helps to force the rings out against the cylinder walls and speed the ring seating and wear process. The other items just need time to wear-in. Also, the cylinder walls must undergo a material transformation where the surface hardens with a carbide wear-resistant coating. On used engines that carbide coating must be taken off with grinding stones before the soft cast iron can be bored with standard cutters. Brake rotors have carbide coatings like that as well and require carbide cutters to machine. I consider my engines to be broken in between 5000-10,000 miles, but that's me.

Modern day engines are automatically cycled on test stands to increase wear and seat rings before they are placed in the car. Before that, dilute oils (break-in oils) were used in new car engines to accelerate the break-in. The new owner was then told to bring back the car after so many miles to have the break-in oil drained and standard oil put in.

As I mentioned before, as long as your oil pressure is OK, hard starting typically goes with how the engine was rebuilt. Friction, in a newly rebuilt engine, requires more torque to turn the engine. Once the engine comes up to operating temperatures, the parts get oiled and run smoother with less friction.

Best regards,

CJR
 
What happens when the engine has been well warmed up and driven some time and turned off .. is it still hard to start hot or only when cold ?

If hard to start hot, then i don't go for the hypothesis of an engine that hasnt been broken in yet. But i havent even stayed at a holiday inn express before so what do i know.
 
Update.

Yes it is hard to start still even after about 1000 miles. Hot or cold its hard to start. Tested the tps its all good. Idle control seems to be working. Changed the cps, no change.

I'm also having a bit of a power drop in the mid rpm range like 2500-4000. Only at wot. When I back off a bit it jumps in power a bit.

I'm thinking map sensor. But I don't think the map would effect starting would it.

Another symptom has shown up as well. While running at idle if I touch the connector to the map sensor and wiggle it a bit the engine starts to stumble.
 
losing prime in fuel line; filter/regulator (silver can on top of fuel pump module)
Put a gauge on it strat it and run it; note pressure; shut off and walk away, come back 10 min later; should still have full pressure in fuel line. if not youre having to crank til pressure builds once again.
that can is available seperately though most parts stores wont find it; strangely if you bring them a part number they see that it is available; youll pay $~90-100;
look on Ebay; thhere are 2 places; 1 in FL and one in CA that regularly sell em for$35 and IIRC ship free. they are EXACTLY the SAME as the ones shown fr triple that on Ebay; same thing same PN same markings when one of each held side X side next to each other. You can replace that and the pump strainers etc all for $100; much cheaper than an assembly from the parts store and if your gas gauge works a whole assembly makes NO sense anyway.
 
Did some research on the check valve. I tried the key on off on off priming procedure about five times, made no difference. And I get a good squirt of fuel pressure at the shradder valve on the fuel rail. Even after an over night cool down.
 
Update.
So I changed the map sensor and everything seemed to get worse. I did find what I think is a damaged wire right at the connector to the map sensor. Is that connector rebuildable or do I need to cut and splice.
 
So just to update this thread. After changing the tps map plugs wires pickup coil and many other cleaning and priming issues. It was the injectors. Picked up some 4hole 703 Chrysler injectors rebuilt and flow checked from a guy on cherokeeforum shipped for 70bucks. Swap took 30min. Solved the problem. Found out I had three injectors leaking heavily after every engine shutdown. Fixed the dip in power at full throttle as well. Easiest mod to the jeep yet and a huge bang for the buck and time.
 
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