Just bought a 91 mazda b2600. The owner was upfront about its issues. It has almost no power. You can’t rev the engine driving along. It’ll just faint and gradually go back to like it was. What’s been changed: fuel pump, fuel filter, pressure regulator, distrib pickup coil. I checked his work and it looks ok. Checked fuel pressure: about 18 should be 28. Gonna do checks on the injectors: leakage, maybe spray pattern etc. Visually they look ok, orings look good. Spark plugs all look good w correct gap. Checked compression: one cyl very low then came up but not like the others which were ok but right at the minimum spec. The owner put in a glass pack muffler. Somebody told me once that reducing exhaust back pressure can define the engine. Don’t know. Help!
That just sounds very low for a electronic fuel injected engine…
I found multiple places saying this: place the pressure gague in line after the fuel filter the pressure should be between 64 - 85 psi. it regulates down to 28 - 37 psi
Rather it is correct or not I can not tell you, but it sounds more realistic then what you posted…
Have you checked the cap and rotor for corrosion and wear?? and plug wires??
With a worn out engine (low compression) you are fighting an uphill battle…
But even if the FP psi should be 28 psi then 18 psi is 36% ish down…
Your guess that the symptom is related to a fuel system problem seems correct. The first step is to figure out why the fuel rail pressure measures 18 rather than 28+ psi. The engine will never run correctly with the fuel pressure at 18. The post above mentions 64-85 after the fuel filter, but I’m guessing that is measuring w/a purposely blocked fuel line; i.e. pump’s dead-head pressure. It’s the 18 psi that’s the problem. Since you have a new fuel filter and new fuel pressure regulator, most likely the replacement pump you installed is defective. That would be my guess Other possibilities
- the voltage input to the pump is low
- there’s some sort of blockage or flow restriction between the pump and the fuel rail.
- the replacement fuel pressure regulator is faulty (there should be no gas in its vacuum line)
- faulty fuel injectors (one or more is stuck open possibly)
I doubt the muffler is the cause. I also doubt the imperfect compression is the cause, although that may be part of the reason the power seems low. But if the engine starts right up, doesn’t require long cranks, compression doesn’t seem like the primary problem you are battling. Suggest to focus your shops attention on correcting the low fuel pressure.
I’d love to see a picture of that old compact truck today. I had a 1991 Mitsubishi Mighty Max. Loved that thing. No modern equivalent.