1993 B2600i weird problem

[philipb446@gmail.com]

I am a newbie to this forum, but have average/above average do it yourself skills.

This is a very weird problem. Truck is a 1993 Mazda b2600i 2wd le-5 stickshift with 163k miles. has slight tick from a lifter going bad (maybe) but no big deal, and no smoke from tailpipe. replaced ECM 20k ago with a NAPA rebuild. truck ran fine. all of a sudden the other day i'm driving and out of the blue it bogs down hard like it is losing fuel pressure and when i hit the gas there is a loud hiss like a vacuum leak coming from somewhere either behind the engine or under it. I pull off, and it stalls (i could keep it running if i feather the gas). i sit there for a minute and it starts right back up and runs fine with no hissing. and i get it home. again today i am driving and the same thing happens again. Any ideas?

[jayratliff12@yahoo.com]

i would check for vacuum leaks with some carb cleaner first, it's the easiest thing to do. if you have some intermittent vacuum leak going to the fuel pressure regulator, it might cause your problem. Usually, a leak in that hose wouldn't cause it to hiss a whole lot. It takes quite a large vacuum leak to cause an audible hissing noise. check for cracks in the hose leading to the brake booster. I've seen a lot of funky problems stemming from a leak in that hose. This is a pretty simple truck, so it shouldn't take too long to track down your problem. Good Luck.

[philipb446@gmail.com]

i would check for vacuum leaks with some carb cleaner first, it's the easiest thing to do. if you have some intermittent vacuum leak going to the fuel pressure regulator, it might cause your problem. Usually, a leak in that hose wouldn't cause it to hiss a whole lot. It takes quite a large vacuum leak to cause an audible hissing noise. check for cracks in the hose leading to the brake booster. I've seen a lot of funky problems stemming from a leak in that hose. This is a pretty simple truck, so it shouldn't take too long to track down your problem. Good Luck.[/b]

Thanks, I'll try that in the am tomorrow. The thing that strikes me is that I cannot replicate the problem in the driveway, no matter how long I run it or how high/often I rev it up. If I can't track down a vacuum leak then it's off to AvPro with the ECM. I'll let you know how it turns out, and thanks for the feedback!


Phil

[philipb446@gmail.com]

Could not find any vacuum leaks, and could not duplicate problem in driveway so I called AvPro and the guy said it is a symptom he has heard of with a bad ECM before so I sent the ECM to AvPro to get rebuilt. I'll let you know what happens when I get it back in a week.

Thanks,

Phil

[philipb446@gmail.com]

Ok, the ECM was not the problem. But I now know what the problem is and I have fixed it. Just want to vent a little first. I sent the Ecm to AvPro and got it back quickly (4 days). the only thing that needed done was some "base adjustment" but it did not need rebuilt, so they did not rebuild it. But that did not stop Avpro from keeping all the money for the rebuild. I saw people say they were concerned as to why AvPro would not take credit cards and that is probably why. I look at it this way, at worst I paid for a lifetime warranty, and/or diagnostic labor so to me it was worth it, but somebody else may think that they shouldn't have paid full price for something that was not done. Lesson is this, I should have done a better job studying and diagnosing before I spent the money. Lesson Learned.

Believe it or not, THE MUFFLER was the problem. Yes that's right, The **** muffler. There was a broken baffle inside the muffler that would intermittently plug the exhaust and cause excessive backpressure. The hissing noise I was hearing was the exhaust gas escaping through a few small holes in the exhaust further upstream when the baffle inside the muffler was restricting it. And when I turned the truck off, the baffle came to rest again and would be fine until I was moving and there was a jarring motion like hitting a bump or something coupled with higher exhaust volume (acceleration) and it would plug up again, loud hiss, etc... This was a maddening problem as the muffler was only 1 year old, and not even rusty yet. I had got it at Carquest for like 40 bucks or something and it too had a lifetime warranty so I got it exchanged and put it on myself. Now all is fine. Nobody else who reads this forum may have this problem ever but I felt it was important to post this so that just in case, it may at least spark someone into checking into their problem further before they waste money. Anyway, I'm so happy to have my little green machine back running like a top again! I think i'll go out and haul some crap around the neighborhood now, just because I can!
Cheers!

Phil