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Ron, ASE Certified Technician
Category: Mazda
Satisfied Customers: 36058
Experience:  35 years as a automotive tech
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99 b3000. I'm getting the following codes-- P1405 P1151

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99 b3000. I'm getting the following codes--
P0302Where do I start?

Hello. My name is ***** ***** I am happy to assist you today. Give me just a moment to review your post, and I'll be right back with the help you need.

You have a DPFE (EGR pressure) code as well as a Bank 2 sensor one HO2S code and two cylinder misfire codes, is the engine actually misfiring?

If you clear all of these codes which ones reset?

Customer: replied 2 months ago.
It might be misfiring a little on acceleration, not sure. It has an exhaust leak right now and the noise from that and poor acceleration, I'm not experienced enough to be sure if I'm just experiencing those things or a misfire. What exactly does a misfire sound like? Is it the same as a backfire?A little recent background-- recently had the head gaskets changed by a non professional mechanic. Afterwards it was running very rough and backfiring badly.I installed a catalytic converter, which was missing, and was getting a p0141 code, so I added the o2 sensor and reset the codes.It was still running pretty rough so I looked up the spark plug wiring diagram and the 4 and 6 wires were swapped wrong. Switched those and it ran much better, although low power and slower than normal acceleration. Drove it awhile this morning and code light came on and got the codes listed above. First time I've seen these codes on this vehicle.Sorry for the long response. Thanks for your patience.

A leaking exhaust system can cause the DPFE code to set and can dilute the exhaust enough to cause a HO2S code to set as well so until the leak is resolved I would ignore the P1405 and the P1151 codes. The codes to focus on would be the misfire codes on cylinders #1 and #2. Because both cylinder misfire codes are coming up and your low on power have you by chance ran a compression test on cylinder #1 and #2?

Customer: replied 2 months ago.
I haven't. I have a compression tester kit that I've never used though so I'll do that and let you know what I find. I'll also tighten down the manifold where it's leaking (it looks like the bolts weren't tightened down completely) and see if that fixes the leak.

If you can fix the exhaust leak you may also solve the DPFE code as well as the HO2S code at the same time. Let read compression on these two cylinders and we can work from there.

Customer: replied 2 months ago.
ok Ron i checked the compression on cylinders 1, 4,5 & 6. Having trouble getting my tester connected to the other two.4,5 & 6 all read between 100 & 105. 1 reads 65.What does that tell you?

Normal compression should be at least 125 to 135 PSI give or take on all cylinders. If your getting 100 and 105 and 65 then you have a worn engine. The cylinder with 65 PSI will not even fire because the compression is just to low. Depending on how many miles you have on the engine a valve job would likely correct this .

Ron and 4 other Mazda Specialists are ready to help you
Customer: replied 2 months ago.
ok gotchya.
Customer: replied 2 months ago.
Weren't the valves done when I had the heads reworked?

Yes they should have been if you had the head reworked.

Customer: replied 2 months ago.
what does that mean? What needs to be done in addition?

If your compression readings are accurate then your machine shop that did the heads need to have another look at there head work. The only other thing that can give you such low compression readings would be worn piston rings and if in fact that is the case you would usually also have smoke out the exhaust as well.

Customer: replied 2 months ago.
Could it be that the heads weren't installed correctly?

That is a slight possibility but more likely the valves where not reworked properly. If there not seating properly it will cause low compression.

Customer: replied 2 months ago.
ok, so take them back to the machine shop and have them re-examine them. Got it.

Yes that is where I would start. Let them know your compression reading as well.

Customer: replied 2 months ago.
ok. will do

Okay thank you as well.