GracefulShanks

Hi all,

I just bought an AT 04 here recently with 85k miles on it. Engine was rebuilt/replaced by Mazda at 59k in 2009. I just had the plugs and coils replaced. Compression is at 145 PSI on each rotor according to the mechanic I bought it from (he didn't do the standard rotary compression test but says he followed the Mazda manual when testing with his standard piston compression gauge).

Here in the last week, my 8 has had trouble maintaining speeds on the highway when going up hills. No matter how much gas I give her, she doesn't accelerate/increase RPM in 4th gear after reaching a max of 3300 RPM or so. The only way it accelearates is by shifting down to 3rd gear and getting up to a max of 4800 RPM and even then it struggles to accelerate to 75mph going up a hill. I can redline in 1st no problem and still has plenty of pull in 2nd as well. The problem starts to come when I need a little more oomph to maintain my cruise control setting of 70-75mph going up these Kansas hills.

So today, my mechanic looked at the fuel pressure and it would reach 60 PSI when turned on and primed, but as soon as I turned the ignition off, the pressure dropped pretty quickly down to about 20 PSI within 3-4 seconds. Also, when he disconnected the fuel line, he noticed he didn't get much gas decompressing through the line AKA spraying gas everywhere like it should when under pressure.

So my problem is obviously a fuel issue and not the Cat or MAF. My question is do I need to replace the entire fuel pump assembly or is there just a certain part that needs to be swapped out?

I found that the going price these days for a fuel pump assembly is around $180 like this one here:
Anyone find a cheaper one lately?

Legot

iTrader: (1)

I would start with a compression test that isn't total BS.

GracefulShanks

I took those results with a grain of salt, but it is somewhat accurate and an indication that engine is doing fine at the moment.


Has anyone else had an issue similar to mine?

Colon Terminus

You say you can redline it in first gear; that indicates that there is no problem in fuel delivery.

I'd follow the previous advice and get a rotary specific compression test at a Mazda dealer. That's the only way you're gonna know the true health of your engine.

GracefulShanks

I probably should do that at some point, but I really don't think it's a compression issue. I don't have any hot start or flooding problems, starts up quick, around 20 mpg (80% highway 20% aggressive city driving), minimal rough idle after cleaning the MAF, ESS, and throttle plate although it is a bit jumpy when warm.

Tonight, I switched back to BP gas versus the grocery store gas I had been using when I first noticed the issue and I also added some fuel system cleaner and the issue seems to have gone away; she runs like a champ again.

Anyone have any thoughts? Could it really have been the brand of gas I was using?

Colon Terminus

It's entirely possible that bad gas was causing your problems. Rotary engines like steady diet of good high octane gas and plenty of it. I had a problem similar to yours with an RX4 and it turned out to be crappy gas.

You should still consider getting that compression test though, just for the peace of mind. I get one annually.

drebbrnator

I have had similar experience with my 8. I am also going to second Colon Terminus. I experimented with regular vs super gas when I first got it, and it runs TERRIBLE on regular, including the symptoms you are mentioning.

Since you didn't mention using regular, I will assume you are a reasonable person, and use super; which brings us to the much less fun issue.

When my fuel pump was failing, it started with starving for fuel at high speed, preventing the car from going above a certain RPM, then became stalling at idle. If your car is doing this; then you have a bad fuel pump. You can buy that pump online; but I would suggest just getting a replacement pump motor instead, as they are much cheaper.
Brand New Custom Electric Intank Fuel Pump w Installation Kit Replacement E8229 | eBay

HOWEVER, if your car is not stalling at idle, you have two other possible options. The least problematic is that some foreign material has wormed it's way into your gas tank, and clogged up the fuel sock. This can be fixed for free, and just involves following the DIYs other forum members have been nice enough to make.
The other option is that your fuel pressure regulator is bad. In theory, your pump should only come on is bursts, and the regulator makes sure a certain pressure isn't exceeded. Since you indicated that your mechanic thought your fuel rail was losing pressure abnormally fast, this could be it. This might also cause your power loss at high rpms, as your fuel pump is having to pressurize the rails, and the return lines that the pressure regulator normally blocks off.

GracefulShanks

Thanks for the response.

Yes, I have been using 91 octane. The only difference is the brand of gas I have been buying. The problem hasn't come back yet, but I'm gonna guess it will come back after I burn through this tank with the fuel system cleaner.

I haven't had the car stall at idle, but the engine has some erratic behavior at idle. Two weeks ago, after I replaced the coils, cleaned the MAF, ESS, and throttle plate and the rough idle I was experiencing when I bought the car was mostly gone, but I did have a jumpy, searching idle. Fast forward two weeks and the rough idle is back but it is not jumpy or searching anymore, it sits at a steady 850 rpm when hot.

I'll look to get a compression test here soon just to be sure I'm didn't buy a dud.

gwilliams6

Generating Power at Full Throttle
• Ignition Coils
• Spark Plugs
• Spark Plug Wires
• Engine Compression
• E-Shaft Sensor (ESS)
• Air Filter
• Intake Valving
• Throttle Body
• Mass Air Flow Sensor (MAF)
• Fuel Pump
• Fuel Injectors
• Catalytic Converter (Cat)

Keeping the Engine at a Cruise
• Ignition Coils
• Spark Plugs
• Spark Plug Wires
• Engine Compression
• E-Shaft Sensor (ESS)
• Intake Valving
• Throttle Body
• Mass Air Flow Sensor (MAF)
• Fuel Pump
• Fuel Injectors
• Front O2 sensor
• Catalytic Converter (Cat)

Keeping the Engine at an Idle
• Ignition Coils
• Spark Plugs
• Spark Plug Wires
• Engine Compression
• E-Shaft Sensor (ESS)
• Mass Air Flow Sensor (MAF)
• Front O2 sensor
• Catalytic Converter (Cat)
• Intake Vaccum

drebbrnator

Rough / searching idle opens up a whole new can of worms.

Most of that is caused by bad fuel air mixture, which is very possibly from a break in your intake system. You can do a quick check of this by getting a 10mm socket, can of carburetor cleaner (or any similar flammable cleaner like wd-40), and a fire extinguisher (ask me how I know).

Use the socket to check that the clamps on your intake air box are snug, and visually inspect it for cracks in the accordion section. Next, start your car up from cold, take that carburetor cleaner, and spray it around the vacuum lines in the engine compartment. If there are any cracks / pinholes in your vacuum lines or intake accordion, your engine will stumble as it sucks in the cleaner.

If you find anything, just replace the vacuum lines, as they are very cheap; the accordion, not so much.

As a sidenote, check those plastic elbows that connect to the intake accordion. They can become brittle over time, and I broke one of mine taking off my intake.