Hi,
New to this forum. I have had 25 plus cars over the years, never a Mazda until this week.

I bought a 1992 B2600i with 159k miles. test run was all good. Bought it and drove it back home 100 miles. Next day all I did was move it a few feet to a different parking spot. Then the day following I ran thru it and looked at the plugs, cap/rotor, air filter....etc. I drained off a qt and added some engine flush oil. Ran for a bit in the driveway and when I hit the road it was like someone had a remote control fuel shutoff switch as it would rev up to 2k rpm then drop immediatly back to idle, then back to 2k rpm then right back to idle (back and forth, over and over). If I keep the rpm under 2k it will continue to run but antyhing past that and it surges like described above. It also smells weird (maybe lean??)

I looked alllll over to see if I knocked off a connector or ?? I did attach a timing light to each plug wire while it was surging and all continued to show current.

What gets me is how well it ran for 100 miles two days earlier.....Help !!!

RH

 

You say you looked at the plugs. Check your firing order, and that the plug wires are still OK, that you didn't damage them.

 

Thanks Cusser. Yah I have traced and re-traced my steps. But of all things.............problem is solved.

I was looking for a good spot to hook up a vacuum guage and found a big one on the aft section of the plenum. Hooked it up, started it up and it revved and held rpm. I almost passed out. Turns out the rubber plug had a funky film on the inside, preventing a proper seal. I still can't believe it.

How it went bad in one 100 mile drive.............I don't know or at this point, care.

Time to swap out the belts, hoses, coolant, check tranny/diff fluids and I'm set.

Thanks.............RH

 

check the converter...seen one stop up like that with all the same symptoms you jus mentioned. we cut it off and truck ran fine...Hope this helps!

 

I have a 1993 B2600i with 171k, runs just fine under 2500rpm, any throttle over 1/4 and it just goes flat and loses all power, driving me nuts...going to try cutting off cat.

 

Or you could pound out all the innards to make a straight-through pipe that still fits !

 

That sounded like a great idea until I looked at it...rusted so bad there is no way to unbolt it, so going to have to just cut it off and throw on a glass pack for now lol

 

Update, so I have only had this truck for a short time. Thanks to all of you help avoid the ol replace this, replace that...8) So what I found is its not the Cat, cut a huge hole right before the cat and went for test drive, starts after about third or fourth turn, then idles and there is full throttle power in all gears with no lag on acceleration. I drove about 5 miles to mini mart, then started it up and started driving, in only about 1 mile, its started running rough and loss of all power past 1/8 to 1/4 throttle, could not go over 2500 rpm, got home and it was idling rough to almost die but not. In the video you will see that full throttle to just falls flat and will not rev up, but just pushing it down a 1/4 throttle it revs right up...so I am an old school Holley and throttle body type knowledge...
This reminds me a choke not turning off...is that possible on this engine?
Perhaps the simpler questions for my next troubleshoot run, is there another function here that would make the fuel lack so badly when it warms up?

A couple notes, there is no water in oil, no white smoke out exhaust, cat has been freed , has new fuel filter and full tune up, wires, cap rotor, plugs, oil change, the temperature when it is warmed up is at 180-195F
Video of performance after warm up.