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kalamykid
kalamykid, Shop Owner/ Tech
Category: Jeep
Satisfied Customers: 3850
Experience:  I HAVE OWNED MY OWN SHOP FOR OVER THREE YEARS. I HAVE THE TOOLS AND SOFTWARE TO ANSWERE ALMOST ANY Q
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I have a 01 grand cherokee with a 4.0, I had to replace the

Customer Question

I have a 01 grand cherokee with a 4.0, I had to replace the head gasket and now the jeep won't start. I have good spark and the spark plugs have fuel on them when cranking. It turns over and back fires through the intake. Only problem I had was when I was doing the work the coil pack fell and broke in half I have a new replacement that I am now using. I know the spark timing is off but I just can't tell how it has no distributor and I didn't touch the timing chain, also it has a new crank sensor and cam sensor, what am I missing?
Submitted: 3 months ago.
Category: Jeep
Expert:  kalamykid replied 3 months ago.

How long did you have the head off of the engine?

Customer: replied 3 months ago.
Sent it to a machine shop to surface it had it off for less than a week
Expert:  kalamykid replied 3 months ago.

Did you pull the lifters and clean them?

Customer: replied 3 months ago.
Didn't pull lifters and was careful when cleaning engine block to make sure nothing fell down in them, rotated engine to tdc on all cylinders and torqued rockers to 22lbs
Expert:  kalamykid replied 3 months ago.

When you pulled the rockers, the lifters may have "pumped up" and are stuck. How long has it been sence you put the rockers back on?

Customer: replied 3 months ago.
It's been together for about 2 weeks but have not been readjusted since, I was so fed up with it I walked away but you may very well be on something here
Expert:  kalamykid replied 3 months ago.

I had one that really made me mad, and the only way I could get it to run was pull the head back off and pull the lifters out, tear them all down and put it all back together again.

Expert:  kalamykid replied 3 months ago.

The only other thing that could have happened was the machine shop did not clip the tips of the valves and the valve shaft is to long after the head was surfaced and a valve job done.

Customer: replied 3 months ago.
Valve job was not done just surfaced, so I doubt anything was done to the valves, what needs to be done to the lifters when taken apart?
Expert:  kalamykid replied 3 months ago.

You have to remove the square lock and pull all of the guts out and clean all of the oil out, then reassemble them, oil them up and put them back in the engine. Make absolute sure that you put each one back in the same hole or you will eat up the cam.

Customer: replied 3 months ago.
Is there a way I can test this theory like lossen all the rockers and bring every cylinder to tdc and tighten the nut just until valve touches rocker and see if that makes it run? What causes the lifter to lock out in full pump up? And also I'm pretty sure this is the second time the cylinder has been machined does something need to be done to the valves?
Expert:  kalamykid replied 3 months ago.

There is a valve in the lifter that will not reliese the pressure till the lifter is pulled apart.

Expert:  kalamykid replied 3 months ago.

You can try loosening them up to see if it will start and then slowly tighten them up.

Customer: replied 3 months ago.
Ok I will try this might be a couple days but I do think you are on something here
Expert:  kalamykid replied 3 months ago.

just let me know how it goes.

Customer: replied 3 months ago.
I loosened the rockers and no change I also have over 130 psi compression on all cylinders
Expert:  kalamykid replied 3 months ago.

You should be getting more like 160-180. How far did you back off of the rockers? Did you do a comp test with the rockers loose?

Customer: replied 3 months ago.
Ok will check that tomorrow
Expert:  kalamykid replied 3 months ago.

OK. Till tomorrow.

Customer: replied 3 months ago.
Ok compression with rockers loose starting from radiator 150,130,130,145,120,150 I know those numbers are down but that seems like enough compression to run maybe not great, It acts just like the timing were off if it had a distributor
Expert:  kalamykid replied 3 months ago.

Cylinders 2,3 and5 are where your problem is. Can you back off the rockers just a little bit more on them and see if the pomp comes up some?

Customer: replied 3 months ago.
The rockers are off
Expert:  kalamykid replied 3 months ago.

If the rockers are off you can not get a good comp test. The valve have to open and close to let air in to compress. Can you put them back on but only thighten them up enough for them to just touch the tops of the valves and them do a comp test so we can have good numbers to go off of please?

Customer: replied 3 months ago.
Ok I had them just touching yesterday and it is doing the same thing it always has, is there anyway ignition timing can get off?
Expert:  kalamykid replied 3 months ago.

NO. With the numbers you have given me, the valves have to be to blame. You did say that you did not have a valve job done on the head correct?

Expert:  kalamykid replied 3 months ago.

I really need to know what the comp is for all the cylinders with the rockers loose as well as with them tight as well so I can see what the numbers are and where we need to go next please.

Customer: replied 3 months ago.
When I tightened the rockers down I have no compression when I lossen them to just touching I have around 150 on all cylinders
When I try to start after they are lose with compression it try's to start but backfires through the intake I also took off timing cover and that is right but chain has slop in it, also the cam sensor is set with a pin through the allignemnt hole.
Customer: replied 3 months ago.
When I twist the cam sensor assembly towards the back of the engine it runs for a couple seconds and then backfires and dies
Expert:  kalamykid replied 3 months ago.

Then we know for sure that the lifters are pumped up to tight. It is backfiring due to the intake valves still open.

Customer: replied 3 months ago.
but with rockers loose doesn't that take that out of the equation being that I have compression now
Expert:  kalamykid replied 3 months ago.

not unless you turn the engine over and made sure that all the rockers where just touching one cylinder at a time.

Customer: replied 3 months ago.
that is what I did and it still won't run
Customer: replied 3 months ago.
I have two problems I guess
Expert:  kalamykid replied 3 months ago.

It sounds like you have a burnt valve as well then.

Customer: replied 3 months ago.
How can I have a burnt valve with 150psi on all cylinders?
Expert:  kalamykid replied 3 months ago.

For this engine to back fire, the intake valve has to open. You can have just a slight opening and still have good test results.

Customer: replied 3 months ago.
Or the spark is occurring at the wrong time
So I am treating the lifters as solid lifters and have valve lash this is a problem but it's not what is keeping it from running can you tell me how the spark is controlled on this?
Expert:  kalamykid replied 3 months ago.

The spark is controlled by the crank sensor, the cam sensor controls the injector timing.

Customer: replied 3 months ago.
I have backed the rockers off so far that they are barely opening the valves it is still backfiring like a distributor is out of time, can a computer cause this? If your out of ideas can this be passed on to someone else?
Expert:  kalamykid replied 3 months ago.

You did not have a valve job done on this head correct?

Customer: replied 3 months ago.
Head was surfaced no valve job, I get where your going with the lifters but I have eliminated that at least enough for it to start by backing them off and I also have 150psi on all 6 cylinders, I seriously doubt I have a bent valve or burnt valve with those numbers, and btw that pressure is staying in for 30 seconds or more
Expert:  kalamykid replied 3 months ago.

If there is any gap between the valve and the valve seat, when the spark burns the fuel in the cylinders the flame can and will go right through the gap and burn what ever air and fuel is in the intake. Once the fuel and air are burnt, the engine cannot run. Pull one spark plug wire off at a time and see if the engine will start. If it does back fire move to the next cylinder and see if you can find the cylinder that is causing the back fire.

Customer: replied 3 months ago.
I don't have a distributor are you familiar with jeeps with a coil bank? If not please send me to someone else, you know dang well if I have that kind of compression the valve isn't leaking
Expert:  kalamykid replied 3 months ago.

I am sorry, I thought you know that you could pull the col pack off, remove the boots and install spark plug wires to the coils and then to the plugs, so you could pull one at a time to see what it would do. I am sorry, I should have made that more clear.