Hesitation and stalling

[SilverXJ]

You will need to do some modification. Larger injectors or piggy back or map adjuster. Running a 100% stock fuel system in open loop will result in some nice tulip shapped valves. I.e. running lean enough to heat the valves up enough for them to deform.

[Don H Jr]

USE your TOOTHPICK, lol. It seems to be the answer for some. My 94' you can put dist in eyball method just as well. Curious to answer to your problem Silver. Mine always ran so well but lately has me stumped still with the cruise bucking an missing in neutral. New coil helped but not the whole answer. Seems your's is in the camsensor/dist postioning. Good luck.

don jr

[Don H Jr]

TONY: the rev limiter effect at 1500 RPM could be PLUGGED CAT COnv.

d jr

[Don H Jr]

SILVER: did a cam change fix this?

D Jr PS That may be my problem too, flat cam lobe. Been clickin' for 10 years cyl 1 or 2 lifter area.

[Tar2001]

Advice needed, pls!

I have the following stroker running for several months already on my 2001 XJ:
258 cranckshaft with 4 counterweights
525 pistons (0.020 overbore)
deck shaved to a clearance of 0.01
Comp cam 231-4 with an adjustable double roller cloyes
SCR sould be around 10 or maybe more, I haven't cc'd the combustion chambers
custom 99+ intake manifold with 2 throttle bodies

The problems I have:
When I open the throttle from idle, the engine always seems to hesitate like choking before reving up, I can even see the rpm needle going down before picking up. Occasionally, if I just blip the throttle or if I suddenly decelerate, the engine stalls.

The stalling problem was much more severe during the early life of the stroker (it used to stall when I lift off the gas pedal during cruising), but I still notice that it is much more frequent when in reverse and suddenly braking to stop.

Another serious problem occurs usually when accelerating very lightly and when the torque converter is locked, the engine seems not very responsive and if u insist on pushing the gas pedal a little more, a very strange problem occurs:
the engine starts hesitating severely like power is shut off and on several times per second until I lift off my foot.
The problem stays even if I go WOT and the transmission is not able to downshift during this problem.

The problem is consistent and now I can even predict the behavior of the engine. Like when i feel it's not responsive I can either push a little less than WOT but enough to downshift before the problem happens, or lift off and go WOT again, then the jeep accelerates like a rocket without a problem.

I know for sure that the porting of the head is not correct, the exhaust ports were enlarged almost to the size of the pre-98 gasket, so they are much larger than the primary tubes!
Could this be the problem?

I also noticed that the camshaft position sensor is not aligned towards the back of the vehicle but rather rotated a few degrees clockwise, is that a problem also?

I am preparing another head to be swaped in along with dough thorley headers, any other suggestions before doing so?

[SilverXJ]

Don, a cam change did fix this problem.

Tar, That sounds like exactly like my symptoms. How did you break the cam in? I would try to re synch the cam sensor and checking other sensors paying particular attention to the MAP and TPS sensor. Before you swap the head you should really fix this problem.

[Tar2001]

Silver, thanks for the reply.

To break in the cam I followed the usual recommendations, if I remember correctly I kept the rpm around 2500 for abt 25 mins as soon as the stroker was fired for the first time.

The cam sensor was supposedly synched on a DRB. Since it looks a bit rotated clockwise, is it enough to synchronize it on the DRB or should the whole thing be remove and then rotated??

I was hoping the new head would fix the problem!

So did u go back to a stock cam? Do you think I should do that? Which cam do you recommend?

[SilverXJ]

I doubt the head will fix the problem unless there is some issue with the valves not sealing, but I doubt that.

The Cam sensor does not need to be synched with the DRB. Use the tooth pick method: http://motorage.search-autoparts.com/mo ... rticle.pdf

Take the sensor out, remove sensor top, find TDC on #1 on the compression stroke, align cam sensor using tooth pick, drop in cam sensor, tighten down cam sensor, remove the tooth pick, and put top back on. It is not terribly important where the plug is pointing, as long as it is reward and the sensor is installed correctly.

Also, did you degree the cam in, or just line the dots up?

If you cam is fried you will need to putt he engine and have it cleaned and replace the cam.

[Tar2001]

Silver, thanks again for the advices.

No the cam was not degreed.
The cam sensor was initially intalled using the toothpick method, and later on when checked on a DRB it showed that it was out of range around 12 degrees. So we rotated it until the reading was close to 0 (may be -1 or 1 deg).

Would that setting be reset if the battery is disconnected for a long time?

Anyway I will try to re synch with the toothpick, and see what come out of it.

So I should not suspect that the extra large exhaust ports in the head might be the cause? Like causing reversion at a specific rpm...?

How can I tell if the camshaft is the actual problem other than by removing and inspecting it?
Could you also please clarify what you mean (put the engine?) in case the cam is fried?
So did you go back to an OEM camshaft

[SilverXJ]

Silver, thanks again for the advices.

No the cam was not degreed.
The cam sensor was initially intalled using the toothpick method, and later on when checked on a DRB it showed that it was out of range around 12 degrees. So we rotated it until the reading was close to 0 (may be -1 or 1 deg).

Would that setting be reset if the battery is disconnected for a long time?

No, the adjustment is physically rotating the cam sensor.

So I should not suspect that the extra large exhaust ports in the head might be the cause? Like causing reversion at a specific rpm...?

Exactly what happened to this head? I was under the assumption that you just had a worn out fatory head.

How can I tell if the camshaft is the actual problem other than by removing and inspecting it?
Could you also please clarify what you mean (put the engine?) in case the cam is fried?
So did you go back to an OEM camshaft

I pulled my pan and saw small metal pieces on the sides of the block and the oil pan. The engine will need to be pulled to clean it of all the metal from the cam. I did not go with am OEM camshaft.

[SIXPAK]

Tar, you may have created at least PART of your problem with the dual TB manifold. The ECM is not able to add enough fuel to balance the inflow of 2 TB's opening at the same time. You could with some linkage make the second TB progressive. This way your primary TB which has the TPS works off idle then anything over 1/4 throttle the second TB would start to open.

[Tar2001]

Sixpak:
I installed this manifold on my 4.0 with a ported head even before the stroker engine was ready and it ran ok for several months without a problem, with an excellent boost above 4000 rpm. In fact it is not the equivalent of 2 throttle bodies, because I have necked each one of them down to around 46mm. I just designed 2 small inserts that can bored to any desirable diameter. I agree with you, it might be causing part of the problem but I am not sure of it, I wonder why it did not affect the 4.0 engine (it only caused the transmission to upshift high gears a little bit early on light throttle because of the distorted TPS reading). But that is not much of a problem with the stroker engine.

Silver:
The guy who ported the head did not see the size of the headers primary tubes, he only had a pre-99 gasket and assume the primaries woud be close in size. So he enlarged some of the exhaust ports to around 37mm or even more (larger than the headers tubes). I only discovered this problem too late... so I had to live with it.

But now I am working on another head myself and I made sure not to enlarge the ports too much. It's almost ready, so I'm wondering whether there's anything else I should check (other than synchronizing the cam sensor, and checking MAP &TPS).

So if my oil and pan contain no metal, I should not worry about a worn cam I guess. In that case, I am also thinking of retarding the cam using the adjustable cloyes gear because my DCR is presently a bit high probably between 8.7 and 8.8.

Thank you guys for the valuable info.

[SilverXJ]

Sixpak:
I installed this manifold on my 4.0 with a ported head even before the stroker engine was ready and it ran ok for several months without a problem,

I didn't catch the fact the you had the dual TB manifold prior. But sixpak is correct that could add to the problem.

Silver:
The guy who ported the head did not see the size of the headers primary tubes, he only had a pre-99 gasket and assume the primaries woud be close in size. So he enlarged some of the exhaust ports to around 37mm or even more (larger than the headers tubes). I only discovered this problem too late... so I had to live with it.

That could be part of the problem as well.

So if my oil and pan contain no metal, I should not worry about a worn cam I guess. In that case, I am also thinking of retarding the cam using the adjustable cloyes gear because my DCR is presently a bit high probably between 8.7 and 8.8.

Not necessarily. You may not see it in the oil. In my case I didn't until I pulled the pan. You could see a sparkly line around each cam lobe.

Now that we are getting all the facts from you its a bit hard to pin down your problem. Between the overly poster head and the dual TB manifold you problem could lie there. On top of the fact that you are running a stock PCM with all these mods on top of the stroker.

What are your goals with this engine? I'm all for doing something different, but you may just going overboard and more problems than it is worth.

[Tar2001]

This car is my daily driver, no off-roading planned. Of course I welcome any potential power gains, specially in the mid and upper range.

I am fairly satisfied with the performance results so far, and the hesitation/choking problem is not that severe but remains a frustration after all the work and efforts done. I am not sure if it is exactly the same symptoms you had with your stroker, but the severe problem only occurs between 1500 and 2000 rpm and usually when slightly trying to accelerate. Choking is always noticed when trying to rev up the engine from idle, and less severe if the AC is on...

Anyway, I will proceed with re-synchronizing the cam sensor, checking other sensors, then trying to inspect the camshaft itself. Im not sure if there's a way to do it without having to actually remove it? Will definitely remove the oil pan before that.

I still have my original intake manifold, might install it with the new head, but I am sure the engine has much more potential than what a bored 60mm or 62mm TB could handle.

Will let you know how it goes.

Many thanks.

[Tar2001]

Solved part of the problem...

The severe problem that used to take place on part throttle is no longer there (described in an earlier post): all I did is I disconnected the map adjuster 10 days ago and the problem disappeared since then.
Resynchronizing the cam sensor did not change anything, but while the oil pump drive was out we noticed some minor play in the shaft. I will replace that one.