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On a 2004 jeep wrangler unlimited if I raise the rear wheels…

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On a 2004 jeep...

On a 2004 jeep wrangler unlimited if I raise the rear wheels off the ground it will run at 80mph and shift though all gears. If I put the wheels on the ground and drive it will only reach about 35mph and bogs down. I also get a flashing check engine light and a code of p0303, p0305, p0300.

Mechanic's Assistant: Does the light stay on, or does it blink?

Blinks

Mechanic's Assistant: Are you fixing your Wrangler Unlimited yourself? What have you tried so far?

New tps. Tried New coil packs. No change. New plugs.

Mechanic's Assistant: Anything else you want the mechanic to know before I connect you?

195000 original miles. Original engine.

Submitted: 6 months ago.Category: Jeep
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Answered in 5 minutes by:
1/2/2018
Jeep Mechanic: Matt, Engineer replied 6 months ago
Matt
Matt, Engineer
Category: Jeep
Satisfied Customers: 23,314
Experience: Honors degree in Mechanical Engineering, worked 8 years as a Formula 1 engine engineer.
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Hello and welcome to Just Answer

This sounds like a lack of fuel and could be a lack of fuel pressure from the electrical pump at the tank.

1st thing to try is to remove the fuel filler cap and then flick the ignition on whilst listening for the brief ‘buzz’ of the pump

If the connections to the pump are corroded or damaged then the pump could stop at any time or could not be running at full speed. Check that its relay switches in and out and the relay contacts are clean and bright – replace the relay if in any doubt and do the same for the fuse,

Ideally measure the pressure at the injector rail (should usually be around 3Bar / 45psi +) and if this is low check the pump as described and also consider changing the fuel filter as if this partially blocked this too will reduce pressure.

You can also get this issue with contaminated fuel , if there’s water or dirt in the tank then either the petrol floats on top of the water or the filter sock on the pump is choked up – so if the other things check out then I’d consider pulling out the fuel pump and cleaning the filter sock

And one other thing to try is to loosen off the fuel filler cap, as there’s a 1 way valve built into the cap to let air into the tank and so prevent a vacuum from being created as the fuel leaves the tank to the engine

If this helps then replace the cap with a new item

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Jeep Mechanic: Matt, Engineer replied 6 months ago

My goal is to give you the best advice that I can and I hope that I've helped today. Please remember to rate my service by selecting from the 5 stars at the top of the screen before you leave. If you need more help, use the reply box to let me know.

If you're not pleased, also let me know because rating bad does not result in a refund, there are better options. Rating now will not close this post nor prevent further replies

Thanks Matt

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Customer reply replied 6 months ago
Fuel pressure running is about 45 or 46 but needle isn't steady. Needle is vibrating between 43 and 48 very fast.
Customer reply replied 6 months ago
If I apply the gas it holds steady at 45psi.
Customer reply replied 6 months ago
After turn car off pressure holds steady at 45psi with out any leak down.
Jeep Mechanic: Matt, Engineer replied 6 months ago

OK

so not a lack of fuel then

I'm assuming that this is the 4.0 ltr 6 cylinder

so I'd consider doing a compression test next to check that the engine is in good health

as all cylinders should be within 10-15 psi of each other

it would also be worth checking that you're getting full throttle?

if you remove the air intake pipe to the engine and with the ignition on but engine off have your assistant slowly press down and hold the accelerator pedal

as the throttle should open smoothly and slowly and stay fully locked open with full throttle

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Customer reply replied 6 months ago
I have full throttle. I will do a compression test and let you know the results.
Jeep Mechanic: Matt, Engineer replied 6 months ago

OK

other possibilities for a lack of power are:

misfiring and you have a general misfire code on all cylinders and identified misfires on cyl5 and 3 so low compression can create this

if this checks out then I'd check the condition of the injector plugs / connections as this could be a lean misfire if an injector isn't firing properly - the best way to check this is with a 'noid' light

http://www.noidlight.com/

Then check all the connections to the engine sensors one at a time, remove each one and examine for signs of corrosion or damage and a squirt of contact cleaner ( not WD40) will also help.

This could be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and leans the engine out causing rough running.

Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.

The best way to locate a leak is to have the engine running and warm and then spray lighter gas around each joint in turn. If the engine rev's up you've found your leak.
Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.

Might also be worth checking the wiring and connector to the airflow meter for any signs of corrosion or damage. you can do a quick fault find if you unplug the meter and run the engine without it.

if the engine condition is the same then chances are the meter or the connection to it is faulty

It’s also worth cleaning the MAF sensor wires, as they can get coated with dirt over time which then offsets the reading
Use some contact cleaner or brake cleaner to spray onto the wires to remove the dirt – on no account touch the wires with anything as they are very fragile

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Customer reply replied 6 months ago
Cylnder 1=125
2=120
3=105
4=120
5=125
6=120
Jeep Mechanic: Matt, Engineer replied 6 months ago

OK

nothing much wrong with those compressions, so at least your piston rings etc are ok

next test is to check the condition of the wiring loom and use a noid light on all the

its also possible 1 or more of the injectors is bunged up or not flowing?

so you could try a bottle of injector cleaner in the tank and also consider having them flow tested / cleaned

although sometimes its cheaper just to replace them with new

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