running lean at wot

while i was at the desert last weekend i would get a ce light and code 51. i usually get this at wide open throttle after about 15 min or so. the only other time i get it is when i am climbing the grade home and at wot. i am wondering if i put a vaccum regulator in line of the fuel pressure regulator to kick the fuel pressure up would it have any effect? i tested the regulator and it works fine all my injectors are fine. my fuel pump is a month old and i took pressure readings at the rail and there fine.

Can you be sure your injectors are fine? If they are the original 14-year-old units, I'd say they're probably a long way from fine and it's time to change them.
Have you done any mods to your 4.0 to increase airflow (intake, bored TB, exhaust, header)?

mark91xjbeef said:

while i was at the desert last weekend i would get a ce light and code 51. i usually get this at wide open throttle after about 15 min or so. the only other time i get it is when i am climbing the grade home and at wot. i am wondering if i put a vaccum regulator in line of the fuel pressure regulator to kick the fuel pressure up would it have any effect? i tested the regulator and it works fine all my injectors are fine. my fuel pump is a month old and i took pressure readings at the rail and there fine.

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After 15 min @ WOT what wrong with this picture?
Need some gears?

about two months ago i swapped in a 96 motor and tested the injectors with everything out and they do pulse fine. i have already re geared the jeep and i have all the bolt on fluff you can buy to give it a little more pep. i have a set of 96 injectors but have been told they are not compatible with the 91 fuel pressure so i used the 91 injectors in the motor swap. any other suggestions

Are you taking the I-15 between Alpine and El Centro to get to the desert? Than I know what youre talking about. For non locals, imagine they put the road over a mountain but you go from sea level to what 4000 ft, 6000 ft. (don't remember) then back to below sea level in something less than 100 miles. So its a steep, straight grade that goes on forever, the rapid elevation change is the first/last few miles on the east side... Fun in the summer when its over 110.

My advice is just to put it in a lower gear, don't use so much throttle and creep up the hill, give up on trying to keep up with v8 powered vehicles.

Also, test your fuel pressure to make sure that your fuel pump and regulator is keeping up with specs UNDER WOT/load not idling, use fuel injector cleaner and change your fuel filter if you haven't done so recently. BTW I always thought injectors usually ran too rich (leaking gas) when old but I could be wrong.

i take the I-8 out to the desert.my gears are fine and don't need to be any lower. at wide open throttle i hold about 70 mph up the grade. i want to know if there are any ways to dump more gas in at wot.

mark91xjbeef said:

i take the I-8 out to the desert.my gears are fine and don't need to be any lower. at wide open throttle i hold about 70 mph up the grade. i want to know if there are any ways to dump more gas in at wot.

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Get a adjustable MAP sensor or build one.
http://www.angelfire.com/my/fan/MAP_adjuster.html

been there tried that. it didnt solve the problem.

Sorry I need coffee I meant to say I-8 thats the road I'm talking about.
Basically you'll be doing the engine a favor (esp in when its really hot in Imperial county) to reduce speed, use a lower gear - transmission not talking about axle gears - to keep the revs up and reduce throttle.

At WOT, I thought the computer favored a rich rather than stoich mix. So something is preventing that from happening. How about the TPS sensor, mine had "dead spots" and I replaced it recently, the effect is very noticeable. If its out of spec the computer isin't accurately compensating for how much the throttle plate wide open. That, and what I say about checking the fuel pressure under wot to make sure the old pump is keeping up with increased fuel demand. I've heard of people taping them pressure gauges to the hood and I've had people buy the meters with some feet of fuel line, hose barbs and clamps to do this. And the fuel filter which if dirty is going to cause fuel starvation under high gasoline demand conditions.

mark91xjbeef said:

been there tried that. it didnt solve the problem.

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Then you need to be sure it is really running lean and not just a bad sensor.
Check the TPS voltage at WOT.

mark91xjbeef said:

i take the I-8 out to the desert.my gears are fine and don't need to be any lower. at wide open throttle i hold about 70 mph up the grade. i want to know if there are any ways to dump more gas in at wot.

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Yes -- replace the injectors.

You didn't give a direct answer about what mods you have, but since you said "all bolt ons available" I assume you have an air tube intake, a hi-flow exhaust, and probably a few more things. All flow more air, without adding any fuel. Your injectors and ECU are calibrated for the stock equipment. Most likely the injectors simply can't flow enough fuel for the conditions you have created. You need t move up to the next larger size.

none of my sensors are bad i went through them all with a multimeter. what else could be done beside buying new injectors?

mark91xjbeef said:

none of my sensors are bad i went through them all with a multimeter. what else could be done beside buying new injectors?

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Run thinner fuel :laugh3: