need help diagnosing low power from new 4.7

[xjay]

I recently built and installed a 4.7 stroker. I did a gasket match port, running about 9.4 comp. ratio, stock valves, comp cam, 24 lb ford injectors, header and 2.5" exhaust, K&N cold air, stock throttle body and electronics.
The problem started with similar power to the stock 4.0 and complete loss of power and dieing above 4000rpm. The plugs are white after a hard pull. I have checked the fuel pressure under load and at idle. It holds at 48-49psi.
Could the computer be leaning out the injector pulse? Could the fuel pump hold pressure but not have the volume?
Thanks for any help you can offer!!!!!!

2000 XJ / 10" custom lift / 37" Iroks / 4.88 gears / ARB, DETROIT /

[Flash]

does it run rough at idle or has a high idle?

[xjay]

No. It's not as smooth as stock but doesn't seem to have a miss.

[Flash]

No. It's not as smooth as stock but doesn't seem to have a miss.

Unplug your o2 sensor (It will set a code) and see if that changes any thing(Maybe its shorted and giving bad info........

Is it possible that the plugs have no color on then because you just haven driven it enough to get color on then?

At 4000 RPM, under load, when its cutting out...........Are you able to read the fuel pressure at that moment.

How about a fuel filter, could be worth a fresh one of those.

Flash

[John]

Good advice from flash, also a simple check is for a pinched fuel line in the system, yes you can have pressure and little or no flow. Check for intake leaks. What valve springs are you using? What year electronics? I am guessing OBDII judging from your fuel pressure. If you warmed the engine to operating temp at 15 - 1800 rpm what color are the plugs?
John

[xjay]

I have about 400 miles on the new motor. The plugs have a little color after warming to operating temp. They look good.
(tanish) It is OBDII. Do you think I will need to build an adjustable MAP???? Has anyone been successful with this on an OBDII system? The valve springs are sb chevy stock springs. not sure of the rate. I will find out. If it was floating the valves, would it loose power consistantly at the same rpm cold or hot? The spring pockets were cut to achieve the proper install height.

[John]

Valve float can be an effective rev limiter cold or hot, but would not explain the white plugs after a hard pull. OBD!! adaptive learning makes for mixed results with a adjustable map sensor. I would look elsewhere first, what is the history of your O2 sensor? Have you scanned the computer to see if any codes are stored. There is codes that do not throw a fault light.
John

[xjay]

I haven't scanned it yet , but will in the morning. It seemed to run better today????? After resetting the pcm, does it take some time for the OBDII to relearn the new perameters? I was also thinking of insatlling a air fuel gauge to monitor the progress. I am looking at a Pro Comp narrow band. Is that compatible with the 2000 xj O2 sensor, or should I be looking at a wide band? Which wire is the signal wire to the O2 sensor?
Do you lose the stored codes if you reset the PCM? I was told that by removing the pos bat cable and touching it to the neg side for about 15 seconds it would erase the stored memory and reset the PCM. Is that correct?

[Alex22]

Valve float at 4000 RPM is very unlikely, the LT-1 Springs are equal to or stronger than the stock Jeep ones. Even with the snarliest RV cam in your engine you shouldn't float the valves until over 5000. But, if your valve springs were used and not checked for pressure at the seat and at full lift it is possible that you have one or more dead springs. So, if you do think it is valve float you could ask your machine shop to check your springs while the head is still in the jeep, it grabs the back side of the rocker arm (next to the pushrod) and pushes down on the rocker arm over the spring with a calibrated torque beam for the pressure. If you find any duds I would suggest a set of new stock springs.

If it is not the springs then it could be a few other things.
Fuel: Like Flash said, it could be a clogged fuel filter. To check if it is a volume problem you could rev it up while a friend watches the fuel pressure gauge (if you have one).
Timing: I would check the wires to the CPS and make sure it is bolted in tight, if it is not then vibrations at higher RPM's could interfere with how well it works.
Computer issues: I don't know much about them so i'll keep quiet on that one.

~Alex

[Flash]

I haven't scanned it yet , but will in the morning. It seemed to run better today????? After resetting the pcm, does it take some time for the OBDII to relearn the new perameters? I was also thinking of insatlling a air fuel gauge to monitor the progress. I am looking at a Pro Comp narrow band. Is that compatible with the 2000 xj O2 sensor, or should I be looking at a wide band? Which wire is the signal wire to the O2 sensor?
Do you lose the stored codes if you reset the PCM? I was told that by removing the pos bat cable and touching it to the neg side for about 15 seconds it would erase the stored memory and reset the PCM. Is that correct? That is corect!

As far as i know, all factory sensor are the narrow band design.

A wide band sensor and a gauge, to read it with, would be helpful

Your ecm is now in Default mode or New ecm mode ..........It hasn't learned its bad habit yet !/!?
If your problem slowly goes back to is before intensity...........the ecm is getting bad info from one of the sensor(Meaning bad sensor or bad wires Most common is forgetting ground and cause the sensor to send bad info to the ecm.)
MY money is still on a shorted o2 sensor. IF the sensor is actually shorted and not just lazy, it will usaly set a code and turn the light on
I have also seen oil soaked connectors cause a lot of grief

[xjay]

Thank you guys for all the ideas!! I am being forces to check codes now, because my check engine light came on today. It has been running great, but I installed the air fuel gauge today to see if infact it was running out of fuel. It pulled hard to 5000rpm 5 times in a row without falling on its face. Yup, then the freekin check engine light came on!!!!! Thats what I get for being lazy and not checking codes first. I'll let you know what I find out.

XJAY

[1bolt]

I think everyone missed the fact that you only have 400 miles on it, the rings probably aren't seated (especially if they are chromoly).

[SilverXJ]

But that wouldn't explain the code(s)

[heartlandoffroad]

What Cam did you put in it?

If it has a any less than a .112 lobe center it will send improper pulses from the MAP to the ECM.

I just fought this problem on a 1998 TJ and it ended up to the cam my customer had the machine shop put in his engine was not OBDII friendly.

[xjay]

The cam is a Comp 68-232-4.
Gross lift is .462/.478
valve timing open close
@.050 is int: 13 btdc 56 abdc
exh: 62 bbdc 13 atdc
duration at .050 is 206/212
lobe seperation 113.0

For now it turns out that the cam sensor was going bad. I scanned for codes and it came up with a p1391. Said it was CKS or CMS. I replaced the crank sensor first, because it simply wouldn't start. It started fine after that. I drove it for a while and it threw the code again. ( check engine light came back on) I turned it off and it wouldn't start again. It ended up being the CAM POSITION SENSOR. It was in about 50 pieces when I removed it from the oil pump drive. It also took out the pick up on the top of the pump drive shaft. So I went to the local pull n save and got a whole new (used) unit for $3.99. What a deal.I haven't driven it yet but will let you know if that fixes All the problems with the power etc....

Xjay