Topic: 2000 Jeep Still Surging

[wefly5]

Well i have replaced it all. Fuel pressure is 49 lbs. Replaced the map. replaced the tps. replaced cap, rotor, Wires
plugs . Still surging around 1900-2200 RPM's

[Jeffy]

Have you checked for CEL codes?

[aw12345]

First of does it surge under full load at that rpm or is this cruising?
Fuel pressure should be checked under full load in top gear to make sure the pump can maintain volume and pressure. If that is good it should do fine under load.
If it surges while at cruise speed start looking at the front 02 sensor, make sure the heater works and it toggles pretty quickly

[sharpxmen]

i'm also thinking O2 but should check for codes first.

and x2 on the fuel pressure under load.

[wefly5]

I have also change to 24 lb fms injectors because i seemed to be running lean. The

injectors gave a little more power but the stumble/surging is still there at like 1900/

2200 rpm's. One thing i have noticed is this does not start happening till the jeep

get up to operating temp . Like around 160 degrees it' in open loop right ?  So can

i just go get me a 160 degree thermostat and keep it in open loop ?

[sharpxmen]

I have also change to 24 lb fms injectors because i seemed to be running lean. The

injectors gave a little more power but the stumble/surging is still there at like 1900/

2200 rpm's. One thing i have noticed is this does not start happening till the jeep

get up to operating temp . Like around 160 degrees it' in open loop right ?  So can

i just go get me a 160 degree thermostat and keep it in open loop ?

your Jeep needs 23.2lb/hr at 49psi if my memory serves me well - depending what injectors you have that can be an issue (what pressure they are rated at for 24lb/hr).
the one that i found assuming you meant ford motor sport as in fms is FMS-M-9593-A302 and it is rated 24lb/hr at 39.15psi which would result in 26.85lb/hr at 49psi on your Jeep - is that the ones you installed? - if that's the case you are at 16% more flow than the stock injectors and you should see a code (CEL) related to an unusual large correction factor.

No, you can't keep it in open loop unless you ditch the O2 sensor - will go in closed loop after about 5 min under normal ambient temps, maybe a bit longer if it's really cold outside

EDIT: what you might have heard regarding the operating temperature is probably related to the O2 heater, when the O2 is at temp will provide the AFR feedback to the computer.

[wefly5]

Ok well i have installed an MSD 6AL and blaster coil......opened the gap up to .035. Jeep still
surging.. but runs better . I have changed all sensors.....cam PS, TPS, O2, the only 1
i haven't changed is the crank PS......could this be the 1 ?. Also the 2.5 has a free flowing exhaust.
Could it be to free flowing. Is the 62mm throttle body the cause ?

I think my next thing will be a digital coil on plug ignition. No moving  parts.

I also installed 24 lbs injectors to see in the surging was coming from a lean
engine.  Again no codes

I had it at the jeep dealer yesterday and they flashed the computer and installed
an update .



Whats the deal.?

[Jeffy]

.035" is the stock gap.  I wouldn't expect to see any change with a MSD.

[wefly5]

Ok ell i have the front O2 unpluged and the senson in the intake the measures air temp. The jeep runs
better and does not surg as bad.

It still has the miss at 2000 rpm's .   

You take off and shift thru the gears and rev the engine to 3100 or so and shift from first to 2nd, when
you let off the clutch and put on the gas the engine bucks........and when you go past 2000 rpm's
the engine will miss 1 time. just miss fire at 2000 .  When you shift to third the same thing happenes.
It is driving me crazy. 

I'm thinking about trading it off.

When you first crank it in the morning and it cold it runs like a top. You can just go thru the gears
and it will even pull 5th gear at 60 mph and 2500 or so rpm's with like 1" of pedel and just cruise right
along effortlessly.

But when it warms up.............a dog.

i'm going to get a 180 thermo and put in it now. and i'm going to unhook the rear O2 also and see
what happens.


PLEASE help if you can !!!

[sharpxmen]

did the dealer put the scanner on it? Might as well since you're stuck. I can start guessing but you might end up replacing parts that are fine so not sure if that is wise or not (since you seem to have replaced a few of them already). I wouldn't run it without the AIT and O2 sensors, defeats the purpose - if you still don't get a code after disconnecting them then there's something wrong there, you should have a CEL quite quickly if you ran it like that.