Bucking underload and moving misfire

2008ms3nick

2008ms3nick

Greenie N00B Member
Hello everyone, first time poster here, I’ve been following this community for awhile with all sorts of help from these threads but I have finally hit a wall with my gen 1. I’ve had the car for about 3 years now, second owner , it has about 150,000 on the dash , I only have a cobb Sri installed. For the last year I have been fighting with this car because I cannot figure out why it is bucking and misfiring under load. At first I thought it was plugs, I changed those to the ngk ix iridium and gapped to .028 and the problem persisted, I then tried coil packs and it still continued, I have replaced the turbo and evap solenoids, i have tried two different MAF sensors, I have replaced the o2 sensors And two injectors and had the other two cleaned with new seals installed and still nothing. The car runs perfectly until I go WOT then it acts as if it’s getting fuel cut. Then yesterday on the way home it threw a cylinder 1 misfire so I cleared the light to get her home and two more misfire codes came on only for it To finally stay on cylinder number 4. So I parked it and came here to look for answers, I have tried to talk to the guys at cork sport but no help there .is there anyone with a similar problem? Am I missing something obvious? I really love this car and want to keep it alive forever, any help would be appreciated.
 
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Welcome to mso officially. Sorry about your luck, has your vvt/timing been done with 150k on the clock? Have you pulled your hpfp and checked it for cleanliness and scoring? Maybe spill valve needs a service, more likely though could be failed pressure relief valve (prv), easy swap unfortunately silly price for a check valve. Checking the hpfp and prv is where I'd start given that you've already done spark plugs, injector cleaning/ seals and coil packs.
 
Awafrican said:
Welcome to mso officially. Sorry about your luck, has your vvt/timing been done with 150k on the clock? Have you pulled your hpfp and checked it for cleanliness and scoring? Maybe spill valve needs a service, more likely though could be failed pressure relief valve (prv), easy swap unfortunately silly price for a check valve. Checking the hpfp and prv is where I'd start given that you've already done spark plugs, injector cleaning/ seals and coil packs.
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Pressure relief valve? Where is that located? And I thought about order the hpfp internals today because I have never looked into it to see if it has scoring but I do religiously run royal purple fuel cleaner in it every 5k
 
You can check the pressure relief valve by monitoring HPFP pressure after a hot shutdown. If your fuel pressure (which should be at ~1000 PSIish) starts dropping after you shut the engine off...its likely the relief valve failed/failing.

The relief valve is on the driver side by where the water exits the block. See picture below, look for the yellow clip thing I am pointing at.

IMG_20200912_094852.jpg
 
Ok thanks guys, when I get off work today I’m gonna try and monitor fuel pressure and check my battery, I saw another thread on this and some said possible bad battery? Ever heard of that? And would the pressure relief valve really cause all this trouble? I mean I’m not second guessing you guys I just wanna learn how these speeds think and act
 
Oh yes pressure relief valve can cause all sorts of fuel issues. The amount of oats between here and Facebook that when someone finally replaces the PRV issue solved.
Bad batteries can cause gremlins, but you'd likely notice issued starting before it's something while driving I'll post a link with voltages to expect, more likely suspect is that the ground near the hpfp is slightly loose.

Edit: forgot link https://www.autobatteries.com/en-us/battery-testing-and-maintenance/car-battery-voltage-and-testing
 
Ok and does anyone have a part number for the pressure relief valve? I called Mazda and he said that he can’t narrow it down because of all the engine sizes -_- no help at all
 
Is it also cleanable? Like does it work the same way as a pcv valve? If I pull it off and test it can I spray it with carb clean?
 
Ok I will check it soon shouldn’t be to hard to remove, I did however see a video where a guy had to pull hiS coolant hoses off? Is that correct ?
 
When I go to plug in the scan tool and check fuel trims and fuel pressure at idle what numbers should I expect as far as short and long term fuel trim
 
Its the high pressure fuel pump pressure after a hot shutdown that you should be monitoring. I dont recommend checking it while at WOT (the only other way I know to diagnose)

As far as removal of the relief valve, get one of these adapters. Makes it much easier.

IMG_20200912_183856.jpg
 
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So I turned the car on today to try and check fuel trims and it was still misfiring on one cylinder which was number 4. I pulled the plugs out after only having them in for 2 days and they look like this (left to right 1-4) what should my next step be? New plugs and a retest? Or is this motor done?
 

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So 15 mins in and I got the pressure release valve out. No coolant lines removed it was a relatively easy removal, now from what I read from you guys I’m supposed to be able to blow through this thing atleast one way right? Well it’s completely clogged no air through either direction and it was corroded into my fuel rail so I have one on order coming in soon hopefully it fixes the issue
 
Well that'll certainly cause an issue, glad you got it out easy hopefully a new one solves the issue, it should based in your findings.
 
Bruh. Why are you using your lungs to test the valve when you have (calibrated) sensors to do it for you?
 
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