Jeep Strokers

I have a customer that has had a 4.6 stroker built and is having problems with it so he brought it to me to look at. Basically it seems like it hits the rev limiter at around 4200-4300 then has a stumble when it comes back to idle until you hit the throttle a couple times then it smooths out. It has 30lb injectors in it but it still shows lean on the plugs. It hasn't ran right since it has been a stroker.

Does the ECM control fuel pump as for voltage?
What could be making the ECM think that it is fat to cut the fuel to the inj.?

It doesn't have any vacuum leaks or codes.


I haven't had much time to look over other stuff just got done tonight and figured that I would post up to see if any of you have had the same problem.

I don't thing you should go any higher then #24 injectors unless there is a turbo or blower involved.

I know you said it was lean, but #50 injector is not going to fix the problem.

Does it have an adj map sensor on it?


Flash

What FMU? OBDI, OBDII, aftermarket?
John

I didn't put the #30 inj in. it I know that wont fix it but it shouldn't hurt it if anything I'd think it should be a little slobbery at idle. I looked at it a little more today. It has the stock Fuel pump and regulator I put a pressure gauge on it and did a pass on the dyno and it seems to be running out of fuel.

It does have a Edge Trail Jammer. I disconnected that and put a stock throttle body on it with a adjustable MAP with no difference.

I have a HV/HP pump and adjustable regulator on order. Hope this fixes it

Yes it is a OBDII

Might be the OBDII system spending too much time decreasing duty cycle of the 39#injectors and getting out of the program mapping, goes into limp mode. Swap the injectors for something smaller and see what change you get.
John

Thanks for the suggestion John I just got done trying that exact thing took a set of #24 off the shelf put them in and still the same thing if not a little worse.

With that check complete, you are likely looking at a electrical/sensor/ecu issue. Fuel pressure checked normal, volume tests might show something. Restrictions could starve it. I have not ran into that issue on Jeep OBDII systems, but it might be there. Keep us posted, interesting.
John

Ok still messing with this thing this is what I've found and done and still with no change.
It will turn the header red after 10 minutes of run time at part throttle
I have put a complete fuel system on it ( pump, adj fpr and upgraded to 3/8 lines ) checked all possibility of vacuum leak ( was none ), synchronized the distributor and moved the ITS to intake tube.
I called a friend of mine that has a 98 Jeep TJ told him to bring it to the shop. I swapped all sensors no change, swapped ECM no change. Checked all grounds and connections no change. tried a adj. MAP it didn't like it at all.

It's not throwing any codes

it is a 1998 TJ
here is the build sheet

Jeep 4.2L 3.895" stroke crank
Jeep 4.2L 5.875" rods
Jeep 4.0L 3.875" standard bore pistons
9.7:1 CR
CompCams #68-231-4 206/214 degree camshaft
Ported HO 1.91"/1.50" cylinder head
Stock 0.051" head gasket
0.081" quench height
head has been ported
it has a 30lb inj.

What RPM does it turn the header red at? I.e. 2000 for 10 minutes? Is this while in neutral?

yep around 2000-2250 in park

That pretty much normal for a OBDII. Happens to mine every time I break a cam in. In park, pushing some RPMS for an extended time the manifold may glow. I've seen it happen on even stock vehicles. The engine is trying to keep a pretty lean condition around 14.5:1 AFR.

I would focus on the original problem. I.e. hits a wall at 4300 RPM. Does it happen while in WOT and driving or park? What plugs? 30# injectors are definitely too large.. what is their part number? Some of those injectors are rated at x# at y psi. So if the Jeep is giving it more pressure than they are rated at it will push the pound rating up. Also, I wouldn't doubt that that it is running rich at WOT above 3500 RPM. My experience has been that the 98+ Jeeps are programed to run richer at WOT above 3500. Meaning that it is getting too much fuel now. I would try to get an adjustable map sensor working though. Also, when are you reading the plugs?

I am reading the plugs rite after a pull on the dyno
I am using CR9's

It will do it both driving and in park.

It will do it at part throttle and at WOT.

Good thinking on the injectors
I don't know what the part # the inj. are I am having my customer getting me the part # as we speak ( Accel doesn't have the p# on the inj.) Yea they could even be a low impedance for all I know.

I did just find out that it does have bigger valves in it than I thought it has 2.02/1.60's I don't think it should make any diff. but I just want you all to know exactly what the engine is.

The valves won't make a difference. I have 26# injectors in my 2000 and it runs rich at WOT... I can dial it out with the apexi though. Since you have access to a dyno, can you get AFR readings? I don't see how the plugs can show a lean condition after a WOT dyno pull if you are running 30# injectors.

Yea I know that is what is baffling me to. Yea I guess I'm going to have to put my wide band O2 on it I was hoping not to (didn't want to weld a bung in the header).

I think putting a wide band on it will answer a lot of questions. One thing that has been bugging me is if you actually indexed the distributor correctly. Sometimes you need to cut the ears off.. check this site out: http://www.angelfire.com/my/fan/dist_index.html

We already ruled out sensors and the computer... what is left is the wiring, distributor, injectors, or an internal issue ( which I doubt)

-Chris