Wont go faster than 10mph
 

Car info: 04 MT 136xxx miles

I have been in the process of doing an engine rebuild and have most of the work done. As of now, the car will idle on it's own and has no leaks. While doing this rebuild we also replaced the clutch and did the air pump delete when I put an OBX header on.

I took the car out for a test drive today after fixing a fuel leak and the CSR wouldn't go above 10mph or around 2500rpm. I never shifted out of first, but I could put the pedal on the floor and it wouldn't go any faster than that, or even seem to try to. If i have the car in neutral it will rev as higah as i want it to. It does have 2 CELs, P2096 and P0171, both for running lean. It doesn't have any other codes.

Any ideas what would cause the engine not going above 10mph? I thought it may be limp mode, but I expected it to throw a code for that besides running lean.

Edit:Can a mod move this to the troubleshooting forum? I'm on my phone at work and clicked the wrong sub forum.

hey checked you intake and make sure there is no unmetered air entering also check you intake seals by spraying some starting fluid around. if your engine revs up you have a leak and are allowing unmetered air into engine

Your car is in "Limp Mode".
Look at these two links
https://www.rx8club.com/attachments/...n-dtcp0171-jpg
https://www.rx8club.com/series-i-tro...-p0302-173317/
https://www.rx8club.com/series-i-tro...-issue-217828/

They both could point to a problem with the exhaust system. All though, you could have two different problems. One with the exhaust and one with the intake.
I found these searching (Google) for the error codes.

Are you going to the EvolvChicago picnic? I won't be there.

Found a loose hose on the intake. No codes anymore, but still have a CEL and still limps around.

Hook up a Vacuum tester and see if you have any more leaks. Don't think its muffler related if it ran ok before. Also ensure the spark plug wires aren't crossed.

Ok. The car starts easily. The idle wanders for the first 10 to 15 seconds then settles and is smooth. Engine revs normally until the car is in gear with the clutch out...at that point it seems to have a limit between 2500 and 3000 rpm. Max speed in first gear is 14 mph.

CEL is still on, but is showing no codes.

Yes, that is a limp mode as Al says, that isn't a vacuum leak. If anything, a vacuum leak would increase the minimum speed, as it would be increasing the volume of uncontrolled air the engine is seeing.

Nearly every limp mode is due to something being hooked up wrong, ESPECIALLY after a major repair job.

I'm not familiar with that specific limp mode (there are several different limp modes), so I am not sure where to point you first.

Did you get the injector harness plugged in right? (common mistake on engine replacements)
Did you clean the e-shaft sensor and reset the sensor profile? (common mistake on engine replacements)

Thanks for the suggestions.

We did the reset using the brake pedal pump and by disconnecting the negative cable. Made no difference.

As near as we can tell the injector harness is correct. Everything layed out neatly in its place. It is always possible that something is where it shouldn't be.

edit:
E shaft sensor is shiny clean.

Given enough of a run it will get up to 4000 rpm in first gear.

Mixed up fuel injector wiring might be onto something.

It's entirely possible to get them wrong, and it's a common mistake.

The more I think about it, the more I think it's the right diagnosis. Open up the throttle, the ECU sees X g/s of air, commands Y amount of fuel to be dumped in, but the injectors aren't firing right, so it's running WAY lean, killing any sort of power. Free-load revving doesn't take much fuel, so that isn't inhibited.

We kept the injectors on the fuel rail and attached to the harness when we pulled it to try and avoid this problem. Unfortunately we had to take the rails on and off several times due to cut o-rings on top of the injectors.

The wire lengths seem to lead to the right location.

Are there two that are more likely than others to be swapped?

Just got done checking the fuel injectors. It appears that they all are put in the correct places according to the info I found here.
https://www.rx8club.com/series-i-tec...-150432/page8/

Any other ideas after checking that?

Likely the MOP...it will cause limp mode with no CEL.....easy way to check...is reset the ECU...throttle will work normally for about 8 sec...then it will stop openning more than about 10%.....

Check it out :) It is easy to damage the switch on the pump if you remove the engine with it still connected

with your symptoms i would start by testing fuel pressure.

Looks like you are on to something. We don't think fuel flow is the issue anymore. It has full throttle movement immediately after start, then after a few seconds barely opens.

We'll try adjusting the MOP switch tomorrow.

Tried adjusting the MOP today. Lined it up with the white marking on top and about 4 other positons, and none of them got the car out of limp mode. Did the battery cable disconnect to reset the ECU every time. Every time it would rev freely for about 10 seconds and then go into limp mode still.



Any other thoughts guys? Kind of running out of options here.

Did you try the way I have had luck doing it?...you can't just pick a spot and hope it works...start at the baseline and then move it a tiny amount at a time...or just swap in another pump

Yes, we moved it in small increments. Adjusted about 15 times total.

if you can't get codes i would stop blindly wasting time on it and find someone who can plug in and tell you what the ECU is setting it in limp mode for exactly.

yes it likely is the OMP, but we don't know that for sure.

FWIW, if you have an iOS or Android phone, Bluetooth OBDII adapters are dirt cheap on Amazon. Grab one and you can check AND clear codes yourself.

Pull the black sensor off the OMP.

Then OHM the wires. One is not connected to anything(I think it is the center but don't quote me on that). While turning the center of the pot. Just a little turn will show nothing. It has to move about half a turn before it starts working. If you see resiatance then the sensor should be good.

Switch was bad. Purchased a used OMP with switch. Problem solved. Thanks guys!

What are you doing with the bad switch?

Right now the old switch is on the workbench in the garage.