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Q: Unable to solve cylinder 4 and 6 misfire on 2001 Mazda Tribute

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Car has 225,000 miles. Engine idles and runs rough. Codes P0304 and P0306 are active. Replaced all 6 spark plugs. IAC valve and MAF sensor were replaced 6 months ago. Swapped coil packs from cylinders 1,2 & 3 with 4,5 & 6. No change. Swapped fuel injectors from cylinders 1,2 & 3 with 4,5 & 6. No change. Checked cylinder compression. Lowest cylinder read 205 PSI, highest cylinder read 215 PSI. P0151 was also active which indicated a problem with the O2 sensor upstream of the cat in the front manifold. I changed that O2 sensor. Still seeing cylinder 4 & 6 misfire no matter what I have tried. Any suggestions? Could it be the PCM?
Yes, it could be the PCM but you need to be sure a s to what isn't happening for cyl's 4 & 6 first. Make sure you're gettiing spark from the coils. if so, check the injector circuits for power and ground. This injection system is ground side controlled, you should have 12 volts on one terminal and no ground until the engine is cranked or is running, then you should see ground as a signal to fire the injectors. I've seen problems in the ground side of these vehicles causing an injector to fail to operate.
I have verified three different ways that the coils are getting power from the PCM. 1. Pulling the coil and hooking it to a spark plug tester I see a good spark. 2. I hooked up a noid (used to test fuel injectors) to each coil pack wire for 4 and 6 and with engine running the noid was flashing. 3. With the engine running I pulled the connector for cylinder 4 and got code P0354 (Ignition coil D primary or secondary circuit malfunction). If I pulled the connector for cylinder 6 I got code P0356 (Ignition coil F ...). Also, if I pull the connector for 4 or 6 I do not notice a change in engine sound or idle quality. However, if I pull 5 (a good cylinder) it is very noticeable. I have also verified the fuel injectors are getting power using the noids. I have checked engine vacuum at the manifold and it is 18 in Hg at idle. Fuel pressure at the schrader valve near the injectors is 53 PSI.
yes but first u need to check for vaccum leak at the pcv hose and the upper to lower intake gasket . these cars are bad about that .
I checked all of the hoses from the manifold to the PCV valve and all are OK. Due to location I was unable to pull the PCV valve. As for manifold gaskets I have replaced the upper to lower manifold gaskets. I have not replaced the lower to head gaskets as that involves removing the fuel injectors. However, I am running out of ideas! I may go ahead and try those.
Ditto that. We see alot of the lower Intake manifold gaskets leaking on these. They are just Oring gaskets and they get hard over time
All, thank you for your help. The problem has finally been found and boy do I feel stupid! I had removed the front valve cover sometime back since the hold down bolt for coil pack #6 had snapped off. When I put the valve cover back on I swapped the connectors for coil packs 4 and 6. Putting the wires back where they belong fixed the problem.
this is the same problem i ran into its very easy to mix the harness wires up always mark your wires thanks for the help
sorry my answer which follows is wrong..but thought i would share my issue....Same issues a lot of you are having the misfire was caused due to leaking valve cover gasket.. the coil paks go down thru the center of valve cover and the seal to keep out the oil was bad so oil leak down into the tube where the spark plugs are and the spark from the coil didn't make to the spark plug (grounding to the block) thus causing the misfire..if you take out the coil pak and see that their is oil on the rubber tubing you have a valve cover leak..hope this helps someone..
I would like to thank one member for admitting stupity. recently changed coil packs and sparkplugs in 2001 mazda tribute, upon restart had bad misfire .went back and switched coil packs and plugs around could not find issue . took in for code ck there were no codes other then a o2 sensor. have been reading all comments here checked wire harness all vacume lines everything I saw here, then saw one I had previously kinda ingored switching coil wires between 4 and 6 . omg was I happy alls well now just a thought some times stupity may be hard to admit but you never know how helpful it can be TYVM
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