1994 Mazda B2300. 2.3L. Fuel injected. Purchased truck about 2 months ago. Drove truck for 1st month, and it ran OK, at best. Truck then sat for 3 weeks and then didn’t start. Engine cranked but did not start. Verified that fuel pump turned on. Measured fuel pressure at 20 PSI, well below spec. Replaced fuel filter and then measured fuel pressure at 40PSI, in spec. Truck still did not start, but sounded better. Pulled plugs, they were dark black with carbon deposits – worst looking plugs I’ve ever seen. Replaced plugs and wires and discover on wire re-install that the previous owner had wires #1 and #2 (on the exhaust side) flip-flopped. Truck has 8 plugs, 2 per cylinder. Truck now starts – runs great for about 2 seconds and then quits. I am in the process of replacing all the vacuum lines, but do not think that is going to solve the problem. Any opinions on what I should focus on next? I was thinking the problem was either the injectors or a computer problem. FYI, the guy I purchased the truck from made a habit of running the gas tank to near empty before refilling.

 

You need to find out what its losing when it dies. Is it losing spark or fuel? I have seen a few bad PCM's that did what you described and were losing reference voltage to the TPS. Could be a lot of things really. Ignition module/coil//fuel pump/clogged converter/MAF ( clean it) come to mind.

 

hixx.....thanks for the reply. Given that the car starts and runs, it must be getting fuel and spark at startup. Do you know how I should go about determining which one is cutting out on me? I don't know how to do this. Thanks.

 

If you have a volt meter check the TPS voltage. You should find a wire with 5 volts on it which is the reference voltage. That comes from the PCM. I suspect you have a fuel pump/regulator problem though since the fuel filter was so clogged. That strains the pump and causes it to pull excessive amps damaging the pump/relay. You need to keep a fuel pressure gauge on it and a voltmeter on the pump. There should be a relay in your relay panel that is the same as the fuel pump relay. Swap those out and look at the terminals of the fuel pump relay. If they are extremely discolored then they have been drawing excessive amps through them which means probable fuel pump damage. Always replace the fuel pressure regulator with the fuel pump.As far as spark just stick a plug on the end of one of the plug wires and watch the spark. The PCM will shut the fuel pump off if it loses its signal from the ignition module however so it can be tricky.

 

hixx...I'm about ready to blow the truck up. I checked the TPS voltage and found the wire w/ 5V on it.I can'tfind the fuel pump relay - is it in the tank? With the fuel pressure gauge hooked up to the fuel rail I had a helper try to start the truck. Fuel pressure stays pinned at 40PSI, never dropped - leads me to believe that the fuel pump is not cutting out. Could it really be the fuel pump or the relay if the fuel pressure measured at the fuel rail appears fine? Hixx...check out this guy's problem...http://forums.mazdaworld.org/index.php?showtopic=22291.....it's identical to mine and he solved it by getting the pcm rebuilt. I pulled the pcm with the intention of looking for the capacitor that he speaks about but my pcm is riveted closed, so there is no way I'm looking at the board without busting the thing open. Don't really know where to go next - I've checked vacuum and that looks pretty good, I'm near convinced that vacuum, compression and spark are not my problem. Will be glad to get more advice - thanks for everything you have offered so far. By the way, my truck is a 94, in my original post I wrote 92.

 

Found fuel pump relay - terminals look normal. Little to no discoloration. FYI, problem is not inertia switch, it's not tripped and I measure continuity across terminals. I checked coil resistances against spec values and everything checked out OK. I checked the resistance across the fuel injector terminals and measured 30 ohms. My manual lists spec at 12-16 ohms. How big a problem is this? Not sure I know exactly what this is telling me.

 

I doubt it would be the injectors. Could be the EEC relay which powers the PCM. It should be in the same panel as the fuel pump relay. You can swap the relays that are the same number. Do you have a fuel pressure gauge on it? If so did it slowly lose fuel pressure or did it remain consistent?

 

Turned out to be the MAF sensor. Took it all apart and gave it a good cleaning. After all the tune-up items that I did, truck runs like new.

 

Good to hear. It was not a total waste of time as you learned alot i'm sure. BTW cleaning the MAF was in my first post on your issue.