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Discussion Starter #1
Hello All. This is my first original post since joining the forum recently. Requesting your help and a sanity check mainly with the fuel pressure test below. I put a lot of background info so sorry if tmi.

O6 X with 143K miles. Had a P0305 code at 141K and with the help from this forum (thanks!), ran through plugs, coils, egr, one-by-one and ended up adjusting valves as they were out of spec.

So about 2K miles later I’m getting occasional stumbling or rough idle when the engine is cold or warm. The X starts but runs at 500-750 rpm on the dash tach and then smooths out. Seems to happen after the car sits for an hour or so but only occasionally – maybe once or twice in 10 starts. Happens with the engine loaded or not, meaning AC/lights on or off.

I cleaned the throttle body including the MAP passage and wiped down the IAT probe (all were not very dirty). Unplugged IAT separately and got high reading code. Then uplugged the MAP and the engine died. Reset codes each time with battery disconnect and did PCM relearn. Thinking it’s not the throttle body.

With my hand on it, checked the blue fuel pump relay under the driver’s side dash to make sure it’s clicking. (Brown one for the PCM is clicking too.)

No vacuum or external fuel leaks.

My X has quick connect fittings so got some connectors from a 2005 Accord from a local pick-a-part yard (see pic). Rigged the fuel line with a rented fuel pressure test kit from Autozone (pic). Confirmed no leaks. Except for the short piece of high pressure hose on the factory connector, the other fuel lines at the T is the regular, unlined 5/16 inch stuff.

So pulled the blue relay and started the car to relieve pressure (pic). Static fuel pressure is running at 54psi with the key on position II. When running, the fuel pressure is almost always at 58psi. Spec for 03-06 is 57-64psi. However, after the engine is turned off the pressure starts dropping and has ranged from 35 to 44psi in 45 mins (5 trials). I was able to recreate the stumbling problem when the pressure was 35, engine loaded, and started the engine like normal (turned the key not waiting 2 secs for the fuel pump to build pressure.) The engine started ran at 500rpm stumbled and then ran up to about 1000 RPM.

To isolate if it’s the fuel pump, reconfigured the test line to only test the pump (pic), primed the line several times with key on position II, and long story short, same falling pressure results in 45 mins. Reconfigured the line back to test pump and injectors and got the same falling pressure results. So, I’m thinking it’s the pump although I did not test just the injectors for leakage.

Here are my questions:

1. How long is the pump supposed to keep the line pressurized?
2. Do you think the readings I got by connecting the pressure gage directly to the fuel feedtube from the tank is an accurate way to check the fuel pump? I made sure the line was primed. It didn’t leak. I’m concerned I bypassed something.
3. Do you think the regular fuel lines in the test rig could have stretched giving false pressure readings?
4. Should I test the injectors? How would you test only the injectors - with air pressure?
5. Any advice, thoughts, am I missing anything?

Thanks a lot in advance!
 

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1. Suspects for fuel pressure drop are fuel pump check valve, injectors, and external pressure regulator (if equipped). Looking at parts catalog views of the fuel rail on 2001 vs. 2006 shows no external regulator on the '06, so you probably have a "Returnless" system. It takes only a very small leak to drop the pressure, since the system volume is small. Based on your pump isolation test, its points to the pump. I assume that you have a good sense of smell and do not sense any gasoline smell around the car.

2. In theory, the system should hold pressure for many hours. The reason for the 2 second prime when you switch power on is there because as systems get older they do tend to leak down a bit. i.e., your situation is not abnormal given the age of the vehicle.

3. DO NOT use air pressure to test fuel systems. You are introducing air under pressure to a system with a substance that can spontaneously ignite under pressure in the presence of oxygen. Remember, that's how diesels work.

4. Link to DIY leak test:

https://youtu.be/NuVfS5ZUGPo


5. Pressure test point: The closer to the delivery portion (fuel rail), the better. E.g. if you had a badly restricted line between the tank and the engine, a test at the pump could show good, but the fuel rail test would fail.

6. Just because pf age, you might want to remove and clean the injectors. You can leak test them at the same time. Use new sealing o-rings when you re-install the injectors. Install them after cleaning, because "Carb Cleaner" solvents can damage them.

7. Have you done an OBD2 scan for pending mis-fire codes?
 

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I'm betting against it being a coil problem, since that would almost certainly throw a P4XX code.

I think you're onto the issue with your (extensive) fuel pressure testing. And there really isn't a whole lot that could cause that. The pressure in the entire system north of the pump should be at the same pressure, so it's safe to say that your pressure IS dropping well below spec, and it's not surprising that would cause stumbling and other issues.

The only things that are likely to cause the problem are the fuel pressure regulator (attached to the pump - apparently the "return line" is internal to the tank), the fuel pickup and/or filter, and the fuel pump itself. Thing is - it seems that only the older (2004 and before, I think) have a separate fuel pressure regulator and pickup assembly. It seems the 2005-6 models have just the fuel pump. Probably your best play is to just replace the fuel pump itself - I really can't imagine that WON'T fix the problem.

FWIW, here is some info for the 2003-4 model - I can't find anything that indicates there's more than just the fuel pump assembly (presumably with any filters and pressure regulators internal to the pump).



Here's a link to an Acura parts dealer showing the configuration of the 2006 fuel system: https://www.acuraoemparts.com/auto-parts/2006/acura/mdx-5-door/prem-trim/5-speed-automatic-engine/electrical-exhaust-heater-fuel-cat/fuel-tank-3-scat
 

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Discussion Starter #4
Bluepill, habbyguy, a quick thanks for the information and advice. Esp the safety advice against using air which I hadn't thought about and the fuel pump diagram. I'm going to continue now so will reference your points and do some more checking, reply back on what I find.

From your comments, I know the system isn't leaking fuel but will check for kinked or damaged lines underneath. I recall seeing posts by habbyguy and forbin404 about checking PCV so will do that too. Re codes, no lights and I'm afraid that I've erased anything with the throttle body work and multiple PCM relearns. That being said, asked my wife and she said the check engine light came on the other day but went off same day while she was running errands. Oh well.

Lastly, you gave me an idea on how to isolate the injectors. I'm thinking a valve or just pinching the hose on my test line between the T and pump will allow me watch the pressure to check if the injectors are leaking. I won't be able to watch the pump side but thinking there would be a large pressure drop when I open the valve or unpinch the hose after 30-45 mins.

Thanks again and will come back with results.
 

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Discussion Starter #5
OK! I'm sure it's the pump - but there is some leakage from the injectors.

Removed and checked the PCV - still has movement. Checked the fuel lines from the tank and all visible lines are good - thanks for the website diagram as that helped me trace the lines.

I reconnected the test line, pressurized the system, and then pinched off the hose between the T and pump so I could read just the injector side (pic). Pinching the hose made the pressure fluctuate a little but it went static at 50psi and lost 4psi after 30 mins. When I released the clamp, the system pressure was 36 confirming most of the pressure loss is coming from the pump! (Pic) (Not too concerned about the absolute numbers as the pinch as mentioned, interfered a little with the pressure.)

So here's what I'm thinking about the pump and injectors:

On rockauto I found the pump for about $83 and the entire assembly with the nut, gasket, and lifetime warranty for about $128 (plus shipping). After studying the pump diagram from habbyguy (thanks!), I'm thinking there's some risk (from my limited skill, old plastic) of breaking some of the plastic tangs on the bottom half to replace just the pump. The $45 premium that includes the nut, gasket, and warranty seems worth it.

With some pressure loss on the injector side, I'm going to clean them with Techron or Seafoam. I watched the injector video from Bluepill (thanks too!) and looks pretty straightforward.

So I'll replace the pump assembly and check to make sure the problem is fixed. Then move to clean the injectors. I'm going to order the pump and will post results after install in a couple weeks because the pump is a week for shipping.

Bluepill, habbyguy, thanks a lot for your help and advice! I really appreciate it!
 

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Discussion Starter #6
Pump arrived Friday and installed it. Looks like the stumbling, rough idle is resolved. Chalk up another win for this forum!

Lot’s of threads and videos out there so this is not a how-to but some observations and pictures of the pump change.

This week while I waited for the pump, since I knew the fuel pressure would drop in about an hour, I tried to always put the key in position II two times to pressurize the fuel line before starting the engine. I was able to avoid the stumbling and rough idle all week.

Took the middle driver’s side seat out the night before, prepped a drop cloth and tray for the old pump. Tank was < ¼ full.

Relieved fuel line pressure. I cranked the engine a few times after the line cleared to reduce the amount of fuel in the line. Battery disconnected. Disconnected the fuel line.

Pump change took about 1.5 hrs including vacuuming the pump area with a mini brush and taking pictures. The area was full of dry, black dust that I didn’t want to fall into the tank or get into the fuel line. The fuel clip and the inside of the connection also needed a wipe down. Went with the Spectra Premium brand from rockauto. Comes with new nut and seal. Has a little louder whirl than the OEM pump but I’m fine with it.

Rented the fuel pump repair kit from Autozone which has a special wrench to take off the nut. You can fasten a socket wrench to it. Worked well. Nut was on stiffer than I expected. Pulled up on the pump fuel line connection and the old pump popped right out. Pulled it out about halfway to let it drain. Left the windows and doors open the whole time to vent the cab. Need to be extremely cautious about sparks, static, flames, electrical cords, etc.

The float on the new pump had to be attached. It was a simple, snap-in process. Only goes in one way so it’s hard to mess up. There’s an over bracket that also snaps-in. Placed the new seal on the pump up to the spring area. Seal has a top and bottom so be watchful. The pump has springs that allow the pump to fit different depth tanks. You place it in and press down on the top so that the spring collapses. Seal goes in tank first then push pump rest of way. I used WD40 on the pump–to-seal interface so that it slid in easily. Also used WD40 on the fuel connection.

Tightened the nut, reconnected the fuel line (book says to use a new clip), reconnected the battery. Placed the key in position II 4 times to prime the pump and line. Checked closely for leaks. Started right-up. Let it run for 7 mins to do the idle/PCM relearn. Filled the tank to approx 1/2 full then went on a test drive with turns and braking to slosh the gas to make sure the nut was sealing.

Started it this morning after the X sat overnight and no sign of stumbling - starts up strong. I’m not going to check the fuel pressure because I’ve taken the quick connect fitting in the engine compartment apart a number of times and don’t want to risk damaging the o-ring to test again. I’m also confident in the pressure testing done last weekend. I’m going to see how it goes over the next week to see if the injectors may need to be cleaned. I bought injector o-rings and have a plenum gasket set in case I have to go down that route.

Hope this helps. Thanks again to habbyguy and Bluepill and to all who ask and contribute to the forum!
 

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Great write-up, LOP... That will no doubt help a lot of folks searching for info on a fuel pump diagnosis / swap. I didn't know there was a rental tool for the fuel pump "cap"... live and learn!

I agree that it would be a waste of time to even bother checking the fuel pressure at this point. Since virtually everything that could cause low fuel pressure (other than a massive fuel leak!) has been replaced with the new pump (with its internal fuel pressure regulator), there's no reason to believe that you didn't fix the problem 100%.

It's always good to see a diagnosis / repair go smoothly - congratulations!
 

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Discussion Starter #8 (Edited)
Thanks again habbyguy!

FWIW since I have some LOPs and in case anybody is interested in the pump construction or wants to replace just the pump unit, here’s a quick post mortem (not a how-to). I did the disassembly on the driveway. Obviously, you’d want to protect it and keep it clean if the plan was to reuse it.

Much easier to remove the pump than I thought it would be – took <10 mins to take it all apart. After 11.5 years, all the tabs were flexible. Used a screw driver and plastic trim tool to carefully bend them. Used a small rubber mallet to tap the housing cover off. Sock filter looked dirty but didn’t appear clogged. There is an internal corrugated looking filter that cannot be replaced. The electrical connectors have the usual tang that have to be depressed to pull apart. Pump has two tangs that hold it in place.

My personal impression is that this is doable (no promises) if you’re careful and don’t mind spending the time. The o-ring sealing the pump at the discharge end to the body had flat spots so it should probably be replaced. If that o-ring leaks, you'll lose pressure in the fuel line. Other risks or unknowns to replace just the pump unit would be the condition of the internal filter and pressure regulator. Recall that this pump was operating just 1-3psi over spec with the engine running, 3psi below spec static. Maybe the internal filter was starting to clog.
 

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Discussion Starter #9
Noticed the test rig and old pump pics are being viewed so adding a couple more pics.

I've got an idea to clean up and use the old pump assembly to test the injectors - basically remove the injector rails from the engine and hook them up to the old pump using the donor connectors. I can then get a 50psi charge and clean with Seafoam or something like it. (I've read that ultrasonics is one of the better ways to clean.) The injectors are about $35 each at rockauto so want to avoid cleaning, if not then clean, and only replace if needed. The X started and ran well all weekend and this morning (3 cold starts and another 10-15 warm or hot starts) with no signs of stumbling so will decide later this week or next to test/clean the injectors.
 

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Kudos to Honda for figuring out how to keep plastic happy in THAT kind of environment for 11 years! The pump does look amazingly "good" - that pickup pre-filter looks a little nasty - might have had enough restriction to reduce your pressure.

I like your idea of using the existing pump to build an injector cleaner bench - I'm thinking that running some Seafoam (or similar) cleaner through an injector would remove anything that was going to be removed from an injector without tearing it down to its base components (something I doubt is possible for us DIYers). And of course, pressurizing it to the low end of its normal working pressure would show any problems with the spray pattern. If you do this, please (!) share photos and any interesting results.
 

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It wouldn't hurt to try replacing the fuel pressure switch, I think that's what it's called? On our 04' it's located drivers side, forward of the rear wheel. Easy to get to and replace. Not an expensive part to throw $ at in hopes of a solution.
 

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Alternate issue/solution for rough idle

Hi all, wow that is intense stuff. Not being a DIY'er but checking this forum for info and education, I took my car to a local shop for a rough idle thinking it may need a valve adjustment - but instead, he said I was low on coolant and when he added coolant and cleaned the throttle body, car is idling at 1000 rpms again, (vs 750-900 when I noticed it a bit rough). I was very happy with this fix and wanted to post in case anyone else searching for 'rough idle' could use this information. Also, reminded me when I was less informed and took this car to the dealer for a rough idle at 85k (many years ago) they convinced me I needed a new timing belt, valve adjustment etc etc and when I think of all the money I spent taking the dealer's advice before getting on this forum... oy, just don't tell my kids how their inheritance has been reduced, lol.

Thanks to all you masters with the real know-how, I hope this "it was that simple this time" information helps anyone looking to educate themselves when sometimes it's that complicated to fix.
 
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Discussion Starter #13
Fuel Pump Update – Broken Tank Nut

Here’s an update to my 06 X fuel pump replacement described which I did back in Sept - about a 1,000 miles ago.

I recently got a CEL code P0455 (large leak) so replaced the gas cap with a known good one from my 08 TL. Reset the CEL with battery disconnect and idle reset. A few days later got the same code plus P0456, (small leak), P0457 (fuel cap loose), and P0497 (low purge flow). Smelled gas a couple times so suspected the evap system, my work on the fuel pump, or my work on fuel line connections where I had disconnected fittings to test and/or replace the pump.

I visually checked the fuel line connections and looked for cracked hoses in the engine compartment - nothing. Also visually checked around the evap pump and related circuit under the X – nothing. So removed the middle seat over the fuel pump port and opened the hatch. Shocked to find that the large plastic nut that seals the pump to the tank had split most of the way. The pump had popped up at an angle about a ½ inch. There wasn’t any pooled fuel but part of the area was shiny wet! Pictures show the nut on the tank with the pump popped up and nut after removal.

So, I had kept the old parts including the factory nut, so rented fuel pump kit 27160 from Autozone, and replaced the nut. Reset the CEL and idle. Checked for leaks, drove around, checked for leaks again, started the engine about 7 times and again this morning. Everything appears OK.

I bought the pump from RockAuto and it came with the nut and gasket so will contact them to see if they will replace the nut.

Other than the issue with the nut, the fuel pump has resolved the rough idle. I’ve had the X sitting for days, up to a full week and it starts right up every time so I don’t think the injectors are also leaking as I had suspected when I first wrote this post.
 

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Yikes! :eek:

Good thing you caught that before something bad happened.

BTW, this is one case where "left over parts" was a good thing... :grin:
 

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LOP, wow. I'm really glad that the (usually nothing but annoying) evap system codes finally helped someone do something "real" to their car! ;-)

Funny how Honda made plastic that looked good after sloshing around soaked in gasoline for 11 years, but the supplier of the new pump couldn't manage to keep their plastic intact for a couple months in a clean environment. Maybe it was a casting flaw or maybe something bad happened to that "nut" before you put it on. I'll certainly try to remember that if I ever end up having to swap out a fuel pump... wouldn't want to have to deal with that in the middle of a road trip!
 
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