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Jared D
Jared D, ASE Certified Technician
Category: Ford
Satisfied Customers: 1355
Experience:  Shop Supervisor at County Fleet
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1992 ford heavy duty 7.5 liter, poor acceleration and bogs

Customer Question

1992 ford heavy duty 7.5 liter, poor acceleration and bogs dowm. did full tune up plugs, wires, cap, rotor, all filters.. no change in performance. will not get up to speed
Submitted: 11 months ago.
Category: Ford
Expert:  Jared D replied 11 months ago.

If you have already done all of that work, the only thing left to check would be an exhaust restriction. With the engine idling, see if the flow from the exhaust is strong enough to push your hand away (thick gloves are a good idea). You shouldn't be able to hold your hand over the pipe for more than a second or so with the engine running if the exhaust is flowing correctly.

Let me know how it looks.

Customer: replied 11 months ago.
I cannot hold exhaust back, it flows good. it idles perfect.. in gear and accelerating is the issue
Expert:  Jared D replied 11 months ago.

Does it feel like it is shifting up too quickly?

Customer: replied 11 months ago.
no
Expert:  Jared D replied 11 months ago.

Do you have a fuel pressure gauge to check pressure from the fuel pump?

Customer: replied 11 months ago.
36 psi, and the pump is 3 weeks old, we did the before everything else sorry!
Expert:  Jared D replied 11 months ago.

Have you checked base timing or engine vacuum?

Customer: replied 11 months ago.
No i have not, I will check them, what should vacuum be? as well as timing?
Customer: replied 11 months ago.
I have 54 kilopascal of vacuum
Customer: replied 11 months ago.
30 degrees advanced timing
Expert:  Jared D replied 11 months ago.

The timing is right.

I was trying to convert kilopascals to PSI. 54kpi (7.8psi) is a little low. Not terrible though. If you pick up the idle to about 2500 rpm what does the vacuum do?

Customer: replied 11 months ago.
it stayed the same, it dropped a hair..
Expert:  Jared D replied 11 months ago.

I think you have an exhaust restriction, most likely in the cat. I think the next step should be disconnecting the exhaust system at the manifold or in front of the cat and see if the acceleration improves as you drive. It's going to be noisy.

Expert:  Jared D replied 11 months ago.

I just wanted to check whether you need any additional info.

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