Need B2500 Engine Specs

[00M6SSLS1]

Hello Everyone,

I'm trying to diagnose a rough idle condition on my dad's 1999 Mazda, B2500.
It's a 2.5L, inline 4 cylinder.

This truck will start with no problem, but will begin to idle poorly after 20-30
seconds. It will also stall if the throttle is slammed shut. Very weak power
overall.

The Haynes manual is far from helpful, there are no specs for compression,
or camshaft dial-in.

I suspect the cam has jumped at least a tooth because the compression is
reading 198-210 PSIg across all four cylinders. According to some forums,
this is about 30-40 PSI too high. My guess is the cam has advanced itself,
or the previous owner did some engine work and did not install it properly.

If anyone can confirm the compression readings for this engine, and also
indicate how to tell the camshaft gear position I would really appreciate it.


Some other measurements taken:
- fuel pressure 70 PSI at idle
- 02 sensors are both responding and crossing from 100 mV to 800 mV
- No DTC codes are present when ODBII port is scanned
- TPS reads fine and responds when probed
- IAT and ECT are working and read the same when starting the motor
- Electronic ignition timing (read by scanner) says 19 degrees (advance)

Fuel injectors have 12 volts and pusle with the engine cranked.
New wires and plugs (all 8 plugs)
New fuel injectors
New IAC valve
EGR valve checked and functional. Have also blocked it off for a test
No apparent vaccum leaks. Hoses look good and are tight fitting.

Thank you in advance for any tips!

 

[Rogue_Wulff]

This is the best timing belt article I have come across for the 95+ 2.3L/2.5L engines.
http://www.therangerstation.com/Magazine/Summer2010/4cyl_timing_belt.htm
My 95 was doing much the same as you describe, and it turned out the cam was 5-6 teeth advanced, and the CPM sensor was at least 120* out of sync. Resetting the timing belt, according to that article, solved all my rough idle/low power/lousy MPG issues. I truely cannot explain how the truck even managed to run *at all*. But, I did buy it for $700......

The above article is what prompted me to join this forum, after having just casually scanned over it the last couple years......

 

[00M6SSLS1]

Thanks so much! I've looked high and low for this simple, yet critical info.

I'm shocked that the Haynes manual does not have this basic info for
cam phasing.

 

[Rogue_Wulff]

Thanks so much! I've looked high and low for this simple, yet critical info.

I'm shocked that the Haynes manual does not have this basic info for
cam phasing.

I looked long and hard trying to find this info, and finally resorted to visiting a freind that has an auto repair shop, and he looked it up on his alldata. Even that wasn't quite as clear and consise as the pics in that article....... Had to really blowup the "pic" (drawing) from alldata, in order to see the specific marks and how they were supposed to be aligned.
The pic of the triangle and diamond marks lined up is, in my opinion, priceless.
I saw the article the day after I reset my timing belt. Since the last person who was in there did it wrong, I was really at a loss as to how it *actually* supposed to be set.
Just as an example of how wrong they had it, they lined up the dimples with the marks on the cover. Here's a quick pic of the cam gear, showing the correct way, and the dimple can be seen 5-6 teeth over.....

And a pic that shows the wrong way to set the aux gear.....

I know the aux gear is incorrect in that pic, but it shows just how far off it was, as it was also lined up with the dimple. The proper mark is a diamond, and is nearly 180* from the triangle mark.

Just for the sake of it, here's the crank gear without the pully, showing how it should be set:

This pic *should* be added to that article.

 

[00M6SSLS1]

It turns out the cam is aligned properly. I guess the compression numbers
are good for this motor.

Can anyone confirm at 200 PSI?

The engine is still idling rough and stalls when the throttle is shut quickly.
Even if you let off the accelerator slowly, the motor really shakes and feels
like it wants to stall.

I used a timing light to measure the spark advance and the marker was
jumping up and down about +/- 10 degrees from zero.

I'm not sure if this is the result of the rough idle, or if the timing is causing
the rough idle.

So...I poked around the coil packs and found what appears to be a filter
with a vacuum line and a two wire connector. Here is a picture of the cap.
If you take it off, and look inside there is a sponge filter.

(sorry that the pics are blurred)

With this removed, the engine idles better. There is another located on
the driver's fender near the brake booster.

Can anyone tell me what these are, and what they do?

What is the function of the vacuum line attached to the coil pack "filter" ?

 

[Sunk]

My truck does the same thing, and has as long as I've owned it. I had in the shop a while back for bad injectors and I was told the air/fuel mixture is too rich when returning to idle and the computer is to blame.

 

[Guest]

I know this thread is over a month old, but not seeing an answer to the question of what the part on the back of the coil is, I thought why not answer it. That is the control unit for the EGR valve. If the EGR is sticking, not closing, the engine will have a very hard time idling. Check the EGR valve and make sure it is clear of deposits, and sealing when the engine is at idle.
Sometimes when the control fails it sends vacuum to the EGR at idle and this will make the engine idle very poor.
Easy enough to tell, just disconnect the vacuum line at the EGR and see if there is vacuum present when at idle. There should be no vacuum. And if the EGR is working and sealing when no vacuum is applied, the idle should improve as soon as the vacuum line is removed if the control is sending vacuum to the EGR at idle.