New Heads - Now hesitates around 40 MPH - Please Help!

[Jim Jermain]

I have a '00 Explorer with the 4.0 OHV. I replaced the cylinder heads due to a rough idle problem at cold start. Before I replaced the heads I tried just about everything else to fix my rough idle problem, (upper / lower intake gaskets, plug wires, plugs, IAC, TPS, EGR Pressure Control, cleaned MAP, fuel filter, one fuel injector - due to misfire code on cylinder 3). After replacing the heads my rough idle problem appears solved. However I am now getting a minor hesitation -stumble on acceleration around 40 MPH.

I can really use some advice. After spending several days replacing the heads, I'm really tired of trying to troubleshoot the Explorer.

Please, please share any tips you may have. The only three things I can think of are the ERG pressure differential hoses (one looked a little worn), the EGR tube o-ring, (the gasket kit that came with the heads did not include this o-ring and my old one was in rough shape. I replaced it with the closest o-ring I could find at my local hardware store) or possibly is the computer re-learning the correct fuel mixture due to the new head. I'm not sure if any of these could cause my problem.

Thanks,

Jim

 

[joe doe]

are you quite sure you got the right heads?

my 2000 ohv needs heads too. now it needs a trans as well. i,m gonna park it until spring . mine fouls out number 4 every other month or so .well actually it cracks the insulator .
i went thru what you did and more .i even replaced all the gaskets on the entire motor ,only to find out i now have a cracked head .i,m pretty bummed.
so i bought a car and parked the thing .kinda tired of the horrible gas mileage anyway .

where did you get the heads?i hope you didnt buy used?did you buy new head bolts?you need new ones ya know.

 

[Jim Jermain]

Thanks for the reply. I did buy new heads. They are from J and C. I'm pretty sure I have the right heads. The truck runs great with the exception of a very slight hesitation under light load. I notice it most when I am going up a hill under light acceleration. If I did it more gas it runs fine.

I'm stumped.

Jim

 

[ranger7ltr]

What is the fuel pressure?

And when did you last change the fuel filter? I will assume that you changed plugs and wires when you changed the heads...

 

[Jim Jermain]

Thanks for the post. The plugs have about 20K on them and the fuel filter has about 5K. I should also mention I checked for codes and nothing came up.

Jim

 

[ranger7ltr]

My take on this ...

I installed a new engine in my 99 Explorer this past spring...New shortblock, new heads from J&C, remanufactured injectors, etc...All in all a new engine...

After running the first 5 to 6k miles, I changed them because I was concerned about wear...They didn't seem damaged and the mixture looked a bit on the lean side on the porcelain but I changed them anyway...There was a difference in mpg of about 2-3 mpg just from the new plugs...I can say I didn't notice any change in the way the engine ran since it was running fine but the fuel mileage increase was significant especially with no change in driving style...

Now I am a bit extreme I guess and change plugs out in any new vehicle or engine after the first 5-10k out of habit plus I like to see the coloration on the plug tips...Yes I did it on the Charger too...

I would consider changing them as well as the fuel filter at this point anyway as well as checking the fuel pressure...On your truck the range of fuel pressure is 55-72 psi with nominal being 65 psi or so and steady...And it does not vary with throttle opening since there is not a vacuum operated fuel pressure regulator mounted on the fuel rail..If the fuel pressure is dropping, there will not be a CEL until the lack of fuel to the engine causes the PCM to throw a lean mixture code...Otherwise the engine will run as it wants...

When I first started driving the Ex the fuel filter would clog up to the point that I could only get to 45-55 mph and the CEL would come on with a lean mixture code... That was because I was not getting the pressure or proper volume the engine needed to run properly... This was thanks to a rusty fuel tank flowing bits of rust into and through the fuel pump and into the inlet side of the filter...Fortunately the filter stopped all that debris but until i changed the tank I was changing filters every 2-3 months...What fun that was...

 

[Jim Jermain]

Thanks for the great suggestions. I will definitely look at the plugs and check the fuel pressure. I picked up a stock Ford EGR tube o-ring so I am going to change that as well.

Since changing the heads my mileage does appear slightly better. I need to confirm, but after driving about 200 miles on the freeway I am just under 1/2 tank.

My cold start problem is pretty much resolved as well so I think the new heads definitely solved that problem.

Jim