Help for my powerless truck



Well, for those of you following the saga with my truck 1994 Mazda B3000 3.0l v6 53,xxx miles… I’m about to pull my hair out. After my ordeal with Pick N Pull today, I have put a new MAF in my truck… Well I just got back in from taking it around the block after letting it sit with the battery unplugged for an hour or so; so that the computer would reset. It idled much better, but when driving it, it’s STILL weak. It’s so slow it’s not even funny.

So, the new, longer list of fixes includes…

New air filter

New fuel filter

New plugs

New wires


New 02 Sensors


2 doses of injector cleaner, no improvement

Fuel pump and fuel pressure check out OK

Distributer checked out OK

Symptoms include

-Very, very slow and underpowered… It’s getting to the point where sometimes I literally am having trouble keeping up with traffic

-Chugging gas (14mpg)

I’m getting so sick of this… I’ve got a set of brand new Bosch Platnium +2 spark plugs going in tomarrow, and we’ll see how that goes. Honestly, after all this, if it’s just the plugs, I’m going to be PISSED. I’m trying to think of what it could be… I’m 99.9% confident that I don’t have any blown seals or gaskets, because all my fluids come out fine, only oil in the oil, only coolant in the coolant, ect, and it has never smoked of any kind. Last oil change it was a quart low when I refilled, but it may have just been that I’m a retard and put 4 quarts in the time before, not 5. The only thing left I can think of is the plugs and the EGR valve/tube, and if the new plugs don’t help, and I have a suspition they won’t, that just leaves the EGR system… Which I don’t know how to test and I can’t afford to fix right now.

Thoughts? Any help is greatly appreciated.


So after resetting things, did you check for any error codes?


It sounds like you might have an exhaust restriction. You can remove the catalytic converter to eyeball any clogging.


I vaguely remember this truck from the old board. Your most likely causes of very sluggish running are:
low compression
retarded timing
clogged converter or muffler

With only 50k+ miles it’s not likely a compression issue unless the vehicle has been overheated in the past. A compression test would verify this.

A clogged converter is possible and this can be verified with a vacuum gauge. Continued operation of a badly running vehicle WILL clog the converter.

The ignition timing is the simplest. Has this been checked? The base timing should be checked only when the test connector is used. Failure to do this means the timing will be severely retarded, which will mean poor running, bad gas mileage, and over time will clog the converter.

A vacuum gauge can also be connected and will let you know quickly if the timing is way off.

Going to another set of new plugs will not cure this problem unless the old “new” ones are total junk.


Three possibilities.

Restricted exhaust
Timing problem (retarded).
EGR open during acceleration.


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Thanks for the help guys :slight_smile:

This morning I went out and unbolted the exhaust after my catalytic converter and peeped in with a flashlight, and everything looked nice and clean, no built up carbon or damage that I could see. HOWEVER, the bolts to unbolt the cat from the downpipes where too rusted for me to get off without stripping, so I couldn’t look in from the other end. So, the catalytic converter is still suspect in my mind, can you elaborate on how to test it with a vacuum gauge?

My Chilton’s manual says that my engine uses a timing chain instead of a belt, and you don’t need to check it or worry about it, and sure enough, there are no timing marks on the crank. So can anyone offer any tips on checking the timing?

Now, For the EGR… Is there a way I could bypass it, like take the valve off and plug the vacuum lines to test and see if it runs better?

Oh and my compression checked out A-Ok…


Does this engine have a throttle position sensor you can check out? If so, the contacts in it may be dirty. Also check for a leaky injector.


Nope, no TPS here.

I put in the set of Bosch +2 plugs, and it’s made a lot of difference. The truck is idling better, doesn’t ‘chug’ when accelerating and has more power. She’s not up to 100% yet, but she’s coming closer.


my dad had the same problem, it was his electronic throttle response


The EGR should open on acceleration unless the engine is cold. You’ll need to follow test procedures to determine if it is working properly though.

To find out about ignition timing, go to the underhood sticker on the truck. This will tell you what you need to know and the sticker ALWAYS takes precedent over anything that any of us may say or what any book may state.

A vacuum gauge is one of the handiest tools around IMHO. I use them all the time, they only take a second to hook up, and can tell you a lot of things once you learn to read it.
If you buy one (they’re cheap) it should come with a pamphlet explaining how to use it and interpret the readings.

In the case of a clogged converter, connect the gauge to manifold vacuum and let the engine idle.
You should have a reading of around 16-20" of vacuum. This varies depending on altitude, barometric pressure, engine conditions (even timing), etc.

This reading (assume 17 for the sake of argument) should be rock steady at idle. When you blip the throttle quickly the reading should drop instantly to zero.
When you snap the throttle closed back to idle the 0 reading should instantly go back to the original 17.

If the needle is slow and/or somewhat jerky returning to 17 then you probably have a clogged converter.

The first thing I would check would be the timing. If someone has been dinking around with the distributor for whatever reason and they are not familiar with a timing test connector, it is very easy to have the timing retarded too much. Depending on the vehicle, setting the timing without use of the test connector may retard the timing by 6 to 10 degrees; and that is a bunch.
Retarding the timing also has the effect of richening the mixture so that could be your mileage problem.
A clogged cat also has the same effect of richening the mix up.

Hope that helps.


Another thing that may be going on is if there is a coolant temperature sensor for the ECU fuel settings, it may be bad and is telling the ECU the engine the coolant is never warming up. Keeping the fuel mixture in a rich condition. By checking the voltage changes across the sensor while the engine is warming up it will tell you if that is correct or not. The sensor is different than the one that is used for the gauge.