P0091 after engine swap

S

Scum

Greenie N00B Member
We just swapped in an ms6 engine into our 2007 ms3. It's running but we get an p0091 code. We haven't moved it out of the garage yet, so just idling with some revs. Totally new to mazdaspeed but not to working on cars. I'm looking for ideas of what to look for. I have torque pro and able to read out the fuel rail pressure. At idle is 50-60ish psi.

I've read the hpfp will boost to 400+ but I'm not seeing the pid to read that.

The car sat for a year so the gas is stale for sure but I can't see it effecting psi. I still have hpfp and stuff from the old engine.

Any guidance would be awesome
 
Hmm. So when I graph it using torque pro, fuel rail pressure as x, it shows 430-500 (a bit bouncy). It doesn't show what the y units are though. When I just create a dial to watch fuel rail pressure, it says 50ish.

I trust the dial gauge since it actually gives the units. So, maybe I'll try swapping the hpfp. I was hoping to avoid ripping into it again but I suppose that's not an option at this point.
 
Check your grounds, one near hpfp should be tight! May need a clean pretty common to cause issues there. Also a ground on the between the passenger motor mount / chassis.

What's fuel pressure readings KOEO? Right now sounds like you're just getting the ITFP pressure none from hpfp. PRV could be toast, or spill valve stuck
 
I'll check koeo when I get back to the car. That was my thought too, it seems like I'm not seeing the hpfp reading OR I am and it's toast. Would it even idle smooth if hpfp was at 50psi? There is some hesitation when I Rev it. Oh, and a lean condition code popped up - no surprise.

Anyone familiar with torque pro and what pid to pull the hpfp?

What is itpf and PRV.
 
Idle would probably not be get but makes sense you get lean when revving not too familiar with torque for PID parameters

Also check that electrical connector on the hpfp.

Itfp= in tank fuel pump, PRV = pressure relief valve, it's on the return from the fuel rail, basically a $70 check valve if it fails open shit pressure and it's not uncommon for it to go after years.

Spill valve can get gunked up too here's a list no to cleaning the hpfp https://mazdaspeeds.org/index.php?t...nd-spill-valve-michael-rey-facebook-kit.8069/
 
OK folks. Back for more advice.

I still have the old engine so we just went brute force with it. We swapped the HPFP (with the spill valve) and the PRV. We checked and retightened all the grounds I could see around the HPFP. We checked the wiring as well, it all looks OK. No change in behavior at all. I should note too, both times we cracked open the fuel lines, there was little more than a dribble of fuel. I was half expecting some high pressure in there but I suppose it confirms the fact that we are not building up pressure - which is part of the reason I'm not bothering changing out the fuel rail pressure sensor. Seems an unlikely issue.

Fuel Rail pressure idles around 70. It'll blip up to about 125 or so if we pop the rpms. We tried driving down the road once and it was horrible. popping and bucking with no power.

I think the only left is the actual fuel pressure regulator in the tank. Is this right? Can you change regulator without having to change the whole pump? Or, am I at the point where I might as well just change the pump and filter while I'm at it?

ANY other ideas of where I should be poking before I get into the pump? Is there another fuel filter in line under the car? Or is the one on the pump the only filter?
 
You're getting 70psi which the amount the in tank pump supplies. I would be looking to swap out the pressure relief valve on the fuel rail as if it's failed open it'll just dump all the fuel pressure building up in the rail.

This is the test procedure for it
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Ya, we swapped that out too. I honestly thought it would be that for sure for exactly the reason you said.

I had only done visual check of wiring. It all looked good in my defense ;) Seriously though, no pinch points or scrub marks. Not your usual suspect problem spots.

Did some continuity checks and found the blue wire from the spill valve to the ecu wasn't making a connection. Other one is. Pulled that whole top wiring harness off to see if it was (hopefully) isolated to that section. That same blue wire was shorting to at least two other wires within that harness. Fortunately, we have that same wiring harness section with the old engine so we are swapping it out now. Obviously it is A problem. I assume (and hope) it is THE problem. Will report back.
 
Woops I see reading your post before that you did do PRV as stated sorry from the skim.

Wiring short could definitely do it, hopefully fixes it.
 
Welp. No joy. It's running better for sure but p0091 still there. Before we weren't even able to make it down the block. This time, we were able to drive around the community but lots of hesitation and bogging. Watching the PSi as we drove, the times it really bogged or hesitated, the psi was dropping down as low as 40.

FYI - I did double check the connection to valve and it's good now. Truly at a loss if it's not the FP.

@Easter Bunny
Your comment makes sense I guess. I'm reading the Fuel rail pressure. Shouldn't that be 400-1600+ since it's after the HPFP. My thinking is if low pressure pump is feeding a drizzle to the HPFP, the HPFP is then boosting pressure up to 70-ish. If it's dropping down to 40, then it's really starving it even more?

I'm clearly trying to talk myself into it being the fuel pump. Though I just pulled the back seat to take a look and, seriously, WTF. I hope the engineer that designed that hole was fired and lives his life in shame as a Walmart greeter knowing he couldn't handle basic geometry.

Please tell me there's some viable trick to getting the FP out? Or that it's really easy to drop the friggin tank. Also, the Mazda dealership in my area has, so far, been a total flop. They don't seem to stock anything so I'm betting they don't have the FP in stock either. Any known issues with just going with something from NAPA or Oreilleys (assuming they have one in stock).

I've got to get this thing in tip-top shape soon. It's my son's car and he's leaving for college in a week. So I really appreciate your pointers and help.
 
The easy way of getting to the tank is to cut the floor

It's not the in tank pump if you want to verify this easily unhook the feed from the hpfp and turn the key on
 
This may not be your issue, but I’ve had multiple issues with the ground wire right near the hpfp even though continuity tests were ok. In the past it stopped my car from turning over and more recently it caused intermittent bucking and a fuel rail pressure sensor CEL.

This last time I sanded the little metal piece at the end of the wire with 600 grit (or something like that) and the plate it attaches to. I also used some deoxit hoping to improve the electrical connection. That fixed it for me.
 
jsilva said:
This may not be your issue, but I’ve had multiple issues with the ground wire right near the hpfp even though continuity tests were ok. In the past it stopped my car from turning over and more recently it caused intermittent bucking and a fuel rail pressure sensor CEL.

This last time I sanded the little metal piece at the end of the wire with 600 grit (or something like that) and the plate it attaches to. I also used some deoxit hoping to improve the electrical connection. That fixed it for me.
Click to expand...
Already been checked...
 
Ya, just to give the warm fuzzy I resistance checked various spots around the block and HPFP area. All 0's, so no resistive connections. I mean, honestly I wish it was that. It would be way easier and cheaper but I'm just not seeing it. Just to confirm though, you guys keep talking about the HPFP ground. There is a ground below it and a ground on the bracket next to it but I don't see a ground attached to it.

Recall, the fuel in the tank sat for nearly a year for this engine swap. So, it's bad fuel for sure. I had planned to drain it last night after we fixed the pressure issue. However, I'm wondering if maybe the bad fuel has plugged up filters. I know there's the filter built into the pump. Is there another inline under the body?

Also, is there a way to resistance or voltage check the FP and Regulator without having to pull it?

@Easter Bunny I'm only challenging because I don't know what else to go after. To my knowledge I've changed out every other possible part with known (was working on previous engine) good parts. Would you say that the FP is good even if pressure is dropping down to 40psi just under normal acceleration and mild load (up a hill)?
 
I guess I haven't replaced the Fuel Rail Sensor. That's the only other part I can think of. But - I'm just not seeing how that is the problem.
 
Check the supply line at the hpfp before you pull the intank pump easy to check before you start cutting the car

Old gas shouldn't clog the filter it wasn't dirty when it got put in the tank and if the cap was closed no more dirt got in

The only filter is the one attached to the pump
 
Thanks. Also realized I haven't checked KOEO fuel pressure which should give me pressure without HPFP interaction. If that's at 70psi, then, yeah FP is fine. If that's garbage, then I feel more confident it's gone south.

I've done a bit of reading on grounds too. I think I'm going to get some heavy gauge wire and run some extra grounds and specifically one to the HPFP directly just to completely eliminate that - even though I'm already reading 0 ohms from negative terminal to HPFP body... Feels like grasping for straws but it's a cheaper investment if it happens to help (cheaper than a $400 FP at least).

Also decided to pull the Spill valve and actually clean it. I swapped it for the one on the original engine - but as I said it's been sitting for a year so I suppose it's possible that both engines spill valves were varnished plugged? Looks like an easy job so might as well try.
 
Awafrican said:
Already been checked...
Click to expand...

I didn’t recall reading that he done anything other than some multimeter checks. Perhaps he did though and I missed it.

What I had meant is that in my own ‘checks’ that ground seemed ok. Even still with the first issue I had to run an extra wire from there to the negative battery terminal to get the engine starting, and the second time (which was after I rebuilt the engine) I had to do as I described about cleaning the surfaces.

I’m not saying that’s the issue. Just giving something else to try, if he hasn’t already.
 
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