2000 Mazda Truck Stalls when driving, misfire after shiftin

Tiny
CANYONCARVER
  • MEMBER
  • 2000 MAZDA TRUCK
  • 4 CYL
  • 2WD
  • MANUAL
  • 156,000 MILES
Baffled here.

The motor starts fine and idles smoothly when cold. Give it a little gas while cold and it starts to misfire like a plug gets fuel fouled. If it dies, it's hard to start. When driving while cold, it dies instantly after pushing the clutch in when rolling to stop.

The motor idles fine when hot. When accelerating and shifting gears, and letting the clutch out, the motor stumbles while attempting to accelerate in higher gear. (Lean misfire?) Shift points around 3k rpm.

Manifold vacuum is at 18-20 in/hg at hot iidle. When checking manifold vacuum, and revving to 2k rpm, motor dies when throttle is closed.

No consistent ECU codes. Have had random "cylinder #1 misfire" and DPSS EGR codes over the past year.
New plugs and wires.
No exhaust blockage.
Vacuum checked EGR valve function, o.K.
New PCV valve.
Spray tested for external vacuum leaks.
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Wednesday, September 30th, 2009 AT 8:59 AM

9 Replies

Tiny
BMRFIXIT
  • EXPERT
WHAT do you have for codes
I would suspect fuel issue and or fuel pump
check fuel pressure and also do a fuel flow test
if fuel check out good
check MAF sensor
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Thursday, October 1st, 2009 AT 6:25 AM
Tiny
CANYONCARVER
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P0301 Cylinder 1 Misfire Detected

This code appears after cold start if I give it too much gas, it dies, and then becomes hard to start. If I avoid the condition that makes it hard to start (like a plug gets fuel fouled) the code will not reappear.

P0402 Exhaust Gas Recirculation Flow Excessive Detected

This is linked to a differential pressure switch that activates the EGR valve. I replaced this switch a while back. The code has reappeared intermittently. I can avoid the driving condition that has caused the code, ie: driving up a long hill on the interstate where I have to downshift and run the motor at a rather high rpm in order to maintain the speed limit.

I will check fuel pressure, but don't think it's the problem. The motor seems to run fine at higher rpms once it gets past the stumbling after shifting.

Beyond checking the MAF connector resistance, are there any other MAF test?
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Thursday, October 1st, 2009 AT 7:05 AM
Tiny
BMRFIXIT
  • EXPERT
You can disconnect the MAF sensor and drive test if better suspect its bad
you can clean it too
check EGR operation as if its leaking internally it would have the same symptoms
remove EGR and check if stuck open
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Thursday, October 1st, 2009 AT 12:53 PM
Tiny
CANYONCARVER
  • MEMBER
Disconnected the MAF and it ran worse. Cleaned the MAF and no improvement.

I removed the EGR and fabricated/installed a block-off plate. No improvement there either.

I guess I'll do a compression test tomorrow.

Thoughts?
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Friday, October 2nd, 2009 AT 9:05 AM
Tiny
BMRFIXIT
  • EXPERT
OK will wait the result
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Friday, October 2nd, 2009 AT 4:13 PM
Tiny
CANYONCARVER
  • MEMBER
The numbers are in. Warm motor, t/b held open, & 4 plugs removed. Front-to-rear.

135
132
138
138

The plugs look the normal creamy tan color.

Another note, if I don't rev the motor over 2500 rpm, it doesn't seem to miss, warm or cold. Yet, while parked, if I rev the motor and hold it for a bit and bring it back to idle, it seems to be missing on one cylinder.

I also vacuum checked the fuel pressure regulatpr & evap canister, and checked the intake manifold and t/b bolts for tightness.

Any advice?
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Tuesday, October 6th, 2009 AT 8:24 PM
Tiny
BMRFIXIT
  • EXPERT
In park or neutral with engine no load
should not take the RPM more than 2500RPM
or internal engine failure will occur
most you can go is 2500rpm for ONLY few sec.
At a time

This is my list of possible causes and what was pass and what test not done yet

POSSIBLE CAUSE:

Ignition system. Was checked and all result came back OK
Fuel injectors?
Fuel pressure. OK
Evaporative Emission system. OK
Base engine. OK
Running out of fuel. OK (NOT running out OF FUEL WE have fuel and fuel pressure )
Camshaft Position (CMP) sensor?
Stuck open EGR Valvesystem OK.
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Tuesday, October 6th, 2009 AT 8:40 PM
Tiny
CANYONCARVER
  • MEMBER
After getting to the end of being frustrated, I finally took it to a local shop to have them look at it. Among other things I told them that the compression was at 132 - 138 across the four cylinders. After they looked at it for a day, they were also baffled. They ran compression and got it in the low 140's. We were both figuring that was significantly different. After doing some more testing, they did the compression again, and a leakdown test. This time compression was low 130's. They ended up looking inside the combustion chambers with a camera, and could see that the exhaust seats were pushed up into the head a ways. Apparently what was happening, was the motor ran fine at low RPM's, and when oil pressure built up at higher RPM's, the lifters were holding the valves away from the seats, not allowing them to seal.

I thought cool. Pay them a coupla hundred bucks for the diagnosis, pull the head myself, and get it rebuilt. That wasn't hard, except when I took the head in for the rebuild, the guy found the head had cracks, two cracks each at the #1, 2 & 3 exhaust seat area. I didn't have the time to go and find another head at the junkyard, so I got a rebuilt head and paid the core charge. Like $550 total for the head with core.

So, in summary, If everything checks out o.K. And it still runs bad, check the valve seats.
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Tuesday, December 29th, 2009 AT 1:29 PM
Tiny
BMRFIXIT
  • EXPERT
Thank you for the update
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Tuesday, December 29th, 2009 AT 6:41 PM

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