Explorer EFI 5.0 Poor Throttle Response

[betzgb]

I have a newly rebuilt explorer 302 with factory EFI and a newly rebuilt 4r70w, Dana 20, and 4:56 gears behind it. Tires are 33". Everything is new or rebuilt including injectors, TPS, BC Bronco throttle cable, etc. The motor starts great, idle is super smooth and the engine runs perfectly down the road with one exception. The throttle response is pretty dismal. When you step into it is gets loud and sounds impressive but accelerates slowly and certainly doesn't press you into your seat at all. Really slow to wind up. From a complete stop, it feels pretty decent starting off, but just feels like it bogs. Suggestions on what to validate that I am getting the most I can from this engine?

 

[onpier55]

I would say that sounds pretty normal. The explorer motors are not a stroker hot rod motor. Have you checked gas mileage? Mine gets up and goes. Not like a hot rod motor. But what does an explorer motor have 200hp?
I have an np 435 and 3:50 gears. Cruises at freeway speeds great.

 

[JKH67302]

I have a similar set up and the only time I would say it is a little boggy is when I'm cruising at slower speeds and the OD drive is on. I assume that is what your feeling too. If what you are experiencing is more serious than that then something else could be going on. The bogging I am referring to is due to a gearing issue. 4.10s are a little tall for this combo. 4.56 or 4.88s would keep the motor in it's happy power place better. Try taking it out of OD more often when cruising at slower speeds. Overall I am very happy with my combo and pleased with the power, but someday I bet I regear.

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[betzgb]

Yes, I wasn't really expecting a thrill ride, but a strong pull through the RPM range and it just seems like something isn't right. I am getting about 13-14 MPG with it. Strong off the line, but at cruise the throttle response is just blah. I have a 74 stock motor with the 3 on a tree and perhaps I am keeping it at higher RPM but it is much more responsive with 33" tires and 3.50 gears. I guess i'll double check compression, make sure the accelerator linkage is getting the throttle body all the way open, and make sure brakes aren't dragging or something silly like that. It has the stock explorer torque convertor in it if that could be a factor to consider as well. Other ideas welcome.

 

[DirtDonk]

Stock torque converter should not be an issue unless it’s defective or worn out.

Definitely check the action of the throttle like you said and make sure it’s opening all the way.
Did you change the ratio at all? That was a common modification to slow down the over-reactiveness of the stock linkage.
But sometimes you go too far and it slows it down too much.

The 4.11‘s and 33s is not out of line for this combination. But it’s not perhaps the perfect combination either.

Your fuel mileage, if that’s a combination of warming up in the driveway and driving around town and maybe a little highway, is not out of line at all. You’re at almost double what the stock one used to be!
Well, maybe one and a half times.

Did you rebuild the motor yourself, or was it done at the shop? Fully assembled by the shop, or by you?
New camshaft, or original explorer?

 

[Timmy390]

Maybe your trans isn't downshifting?

Tim

 

[JKH67302]

Dirtdonk makes a great point. Check the throttle linkage. I use the stock cable and a custom bracket for the throttle body. My setup is pretty similar to what would be on the explorer. The BC cable might be changing the ratio some or maybe it is adjustable?

I also agree that the 4.10s and 33s are really good together, it's really just an OD thing where it can be undesirable at lower speeds. If you compare this setup to your 74 motor and 3 speed it should be a huge performance upgrade, or at least it was for me conparing my old carbed 302 and C4. Food for thought.

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[betzgb]

Dirtdonk makes a great point. Check the throttle linkage. I use the stock cable and a custom bracket for the throttle body. My setup is pretty similar to what would be on the explorer. The BC cable might be changing the ratio some or maybe it is adjustable?

I also agree that the 4.10s and 33s are really good together, it's really just an OD thing where it can be undesirable at lower speeds. If you compare this setup to your 74 motor and 3 speed it should be a huge performance upgrade, or at least it was for me conparing my old carbed 302 and C4. Food for thought.

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Exactly! I was expecting to see an improvement and it definitely has less throttle response compared to my carbed 302. As for the motor, I had a machine shop prep the old explorer block (clean, check, hone) and I did the assembly myself. Used the explorer cam, pistons, rods and crank. Stock explorer motor all the way around just re-ringed, new bearings, pumps, gaskets, etc. It is a new torque convertor but ordered as a stock replacement to the transmission from Rockauto. I rebuilt the transmission as well. The transmission seems to downshift fine as I am often opening the throttle pretty wide just to get er moving up and down hills, passing another car, etc. I used the BC bronco throttle cable and it seems to work fine but does not have the pulley type stock cable setup that the explorer had which I assume slows the opening. The fuel mileage is a mix of all as we do have a fair bit of city roads/highways around here. Where is the sweet spot rpm range for this motor? I'll try with overdrive off and on at different speeds and see what RPM range and see if it still feels doggish in that range.

 

[betzgb]

Exactly! I was expecting to see an improvement and it definitely has less throttle response compared to my carbed 302. As for the motor, I had a machine shop prep the old explorer block (clean, check, hone) and I did the assembly myself. Used the explorer cam, pistons, rods and crank. Stock explorer motor all the way around just re-ringed, new bearings, pumps, gaskets, etc. It is a new torque convertor but ordered as a stock replacement to the transmission from Rockauto. I rebuilt the transmission as well. The transmission seems to downshift fine as I am often opening the throttle pretty wide just to get er moving up and down hills, passing another car, etc. I used the BC bronco throttle cable and it seems to work fine but does not have the pulley type stock cable setup that the explorer had which I assume slows the opening. The fuel mileage is a mix of all as we do have a fair bit of city roads/highways around here. Where is the sweet spot or range for this motor? I'll try with overdrive off and on at different speeds and see what RPM range and see if it still feels doggish in that range.

Also, shorty headers into 2 to 1 Bronco hut - 3" exhaust system for what that is worth.

 

[JKH67302]

I'm running the same exhaust, so another similarity with different results.

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[betzgb]

Quick update on this one. I just installed the hard top this weekend and went for a joy ride. With the reduction in wind/road noise I was able to hear an exhaust leak on the passenger side. So that gives me a new path to work down. As I mentioned, I have the Bronco Hut exhaust kit which has Sanderson shorty headers and a customer two into 1 pipe setup with a ball/flange connection at the header.

 

[73azbronco]

the 302 is at best marginal in moving an EB. Have you driven others with a 5.0? An exhaust leak could be playing with your O2 sensor.

How is timing?

What is fuel pressure?

 

[Broncobowsher]

Little late to this one. But it I were to pick one thing I would say the gearing is on the economy side and that is what you are getting. Bronco on 33s getting 14 MPG is an economy gear. I was running 4.88 gears with 33s and the 4R70W and thought they were pretty good highway gears for a Bronco. It was a 351, but remember thinking of how it would be a really good match to a 302.

4.11 gears were a real good choice for 33s when you don't have an overdrive transmission (C4, NP435, etc.)

 

[EFI Guy]

^^^What he said. With 33's you'd need to be at 4.56 just to match the final ratio of the Explorer. I'd go 4.88 if you are wanting better throttle response than the stock Explorer.

 

[duffymahoney]

I have 4.56 and 4r70w and 32". Response is great

 

[betzgb]

Sorry! Typo in the original post. Too many projects…. This truck has 4.56 gears.


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[DirtDonk]

And let’s get some thing clarified here. Are your tires 33‘s, or are they 33’s?
The difference being are they flotation sizes that have a rating of 33 inches, or are they metric that you’re calling 33?
For example, if they are 33x12.50x15 then they are probably between 31 and 32 inches.
But if they are metric, they’re probably bigger and heavier than those other 33‘s.

 

[EFI Guy]

Sorry! Typo in the original post. Too many projects…. This truck has 4.56 gears.

Well then it shouldn't be a slouch, but I wouldn't expect it to pass the $100 bill taped to the dashboard test either. Definitely get your exhaust leak fixed so that you know that it isn't skewing fuel trims.
Then I'd pick up an OBDlinkMX+ or a Vgate Vlinker FS. From there I can remote in and get you set up to datalog. Then you can just email me the file after a couple of pulls and I'll look to see if everything looks right.

 

[betzgb]

Well then it shouldn't be a slouch, but I wouldn't expect it to pass the $100 bill taped to the dashboard test either. Definitely get your exhaust leak fixed so that you know that it isn't skewing fuel trims.
Then I'd pick up an OBDlinkMX+ or a Vgate Vlinker FS. From there I can remote in and get you set up to datalog. Then you can just email me the file after a couple of pulls and I'll look to see if everything looks right.

Thanks Garry! I will order a OBD device and get back to you when ready to remote in. In the meantime I will chase the exhaust leak and see if behavior changes.

 

[duffymahoney]

Could the trans be the issue?