Performance issues 1986 302
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Performance issues 1986 302
Ok, this is the same 1986 F250 I've been asking for advice on.
It has an EFI 302 with a New Process granny low four speed. Also has 3.55 gears, and 33 inch mud tires
4th gear in this truck is gutless. It will hardly accelerate, and will barely get up to 65 on a flat road. Any grade and it loses speed, will get up to 75-80 going downhill with a tailwind, but is back to 65 once you hit flat ground.
It's a brand new 302. New plugs, wires, distributor, icm, coil, high pressure fuel pump, fuel filter, just about everything. Timing is dead on according to the timing light, and the advance is working.
I'm thinking it's a clogged cat causing my issue, but I wanted opinions and ideas to test before just hacking off the cat.
Thanks in advance!
It has an EFI 302 with a New Process granny low four speed. Also has 3.55 gears, and 33 inch mud tires
4th gear in this truck is gutless. It will hardly accelerate, and will barely get up to 65 on a flat road. Any grade and it loses speed, will get up to 75-80 going downhill with a tailwind, but is back to 65 once you hit flat ground.
It's a brand new 302. New plugs, wires, distributor, icm, coil, high pressure fuel pump, fuel filter, just about everything. Timing is dead on according to the timing light, and the advance is working.
I'm thinking it's a clogged cat causing my issue, but I wanted opinions and ideas to test before just hacking off the cat.
Thanks in advance!
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Joined: Jul 2010
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From: Northeast, OK
A clogged cat can give those symptoms. However, your engine produces little power at low RPM and yet your gearing forces it to run at low revs.
Ford geared most of the trucks with 351 engines to run at about 2700 RPM @ 60 MPH. And the 351's have much more torque at low rev's than your 302 does. But with your big tires your engine is turning more like 2100 RPM @ 60 MPH.
So, before you cut the cat off, try shifting into 3rd. At 60 MPH your engine will be spinning 3600 RPM (the NP435 has 1.66:1 gearing in 3rd), which is well into its power band. If it pulls hills like a champ then your problem is gearing. But if it still bogs on hills then you may have an exhaust problem.
I say "may have an exhaust problem" because it may be an engine problem. Have you checked to see if the computer is throwing any codes?
Ford geared most of the trucks with 351 engines to run at about 2700 RPM @ 60 MPH. And the 351's have much more torque at low rev's than your 302 does. But with your big tires your engine is turning more like 2100 RPM @ 60 MPH.
So, before you cut the cat off, try shifting into 3rd. At 60 MPH your engine will be spinning 3600 RPM (the NP435 has 1.66:1 gearing in 3rd), which is well into its power band. If it pulls hills like a champ then your problem is gearing. But if it still bogs on hills then you may have an exhaust problem.
I say "may have an exhaust problem" because it may be an engine problem. Have you checked to see if the computer is throwing any codes?
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From: Virginia
It's the tires and the gear ratio. The 302 is a very small engine for a f150 when they are stock, f250 is even worse. It's really bad when oversized tires are added. Get rid of the large tires or go to a 4.10 or higher gear. You can do a little math or some of the guys on here can help you do the math if you tell them the tranny you have. They can tell you if a 4.10 gear would be close to leaving your tranny in 3rd gear. You can then drive around in 3rd and see what it would be like. You never know, you may need 4.56 gears.
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It pulls hill like a champion in 3rd, but I don't have a tach and I was afraid of leaving it in 3rd and over-revving the motor.
It just threw me off that it wouldn't maintain speed on a level road after it had gotten up to 75 going down a hill.
Truck isn't throwing any codes at the moment. I'm about to pull the injectors and clean them though, as they are the original injectors to the truck.
The two reasons I was looking at the cat, is that I had a Jeep that acted the same way and it was a completely different truck after I gutted the cat, and the mesh in the one cat I still have on the truck glows some while driving the truck.
It just threw me off that it wouldn't maintain speed on a level road after it had gotten up to 75 going down a hill.
Truck isn't throwing any codes at the moment. I'm about to pull the injectors and clean them though, as they are the original injectors to the truck.
The two reasons I was looking at the cat, is that I had a Jeep that acted the same way and it was a completely different truck after I gutted the cat, and the mesh in the one cat I still have on the truck glows some while driving the truck.
FTE Legend
Joined: Jun 2006
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From: Ottawa, Ontario
That is not possible, the electronics will limit rpms before the mechanical limits are reached and that is up around 5500rpm.
That is because a 302 really isn't enough motor for a heavy truck, but there is lots of room to improve your motor too.
There are lots of reasons this motor is underperforming, primarilly it's because of the stock cam and heads but the stock cats are restrictive too even if they aren't clogged.
That means it's doing its job but how do you know it glows?
That means it's doing its job but how do you know it glows?
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My exhaust is cut off shortly after the first cat. So I can get under the truck and actually see the mesh inside of it.
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From: Virginia
The cat does get hot, part of the way it works. I can't recommend you gut or get rid of the cat, but obviously you do not have inspections if you have the exhaust cut off that far up front. In my area the exhaust has to exit so many inches beyond the cab for obvious reasons.
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