2.5 Soob Engine Starting Bogey
 

Hi all from always hot humid and gusty Panama.

Cut to the chase. My engine is rebuilt ground up and has great performance. After sitting a month recently (traveling) it wouldnt start. Squirted gas into the TB and she sputtered and lit. Ran fine. Then she wouldnt again and again. Cleaned the MAF - brightened up some oxidized (male) leads off coil pack, tested TPS - fine. Reset computer. Started great.

Two weeks later, same issue.
Tried to start over and over - no joy. Then she finally caught but sounded really really rough like it wasn't firing on all cylinders, that smoothed out and she ran well after that. After shutdown while warm I tried again and she wouldnt start, then I let the fuel pressurize longer than usual (she pressurizes and then stops as it should, but I waited) and she started a few times in a row.

What could be going on here!?

Is there a way to check if the MAF is going without using a scope (I dont have one)?

Since I have an 94 Forrester (same engine as my 02 on my gyroplane) should I just swap out the one from my plane and if that goes away -order a new MAF?

One additional note: I recently installed Iridium plugs.... doesnt seem like that would affect start only right?

Any suggestions!???? (In simple terms and step by step because as we have already established I have no business turning a wrench - ha)

I have a 2000 sohc 2.5 engine that had a similar problem. Mine was fuel pressure related. Mine would fire up for about a second and then die but only when warm. I had to let the fuel pump pressure up for about ten seconds and then it would start fine. I have an aftermarket aeromotive fuel pressure regulator that doesn't leave the system pressurized. I never had a issue with it starting cold. My problem was acting like a bad ect sensor but I changed it twice, it could be your problem though.

Fuel pressure is a good place to check, but also check the throttle position sensor. That can make it run rough or not at all for some throttle settings.

By the way...I'm about halfway through my 2.2 overhaul...got my new Air Trike re-drive and am really impressed.

The Air Trike re drive has been very good for me so far. I am running pure synth in it (after doing the flush they recommend after the first high rpm run up). Changed it at 30 hours just because Im superstitious. No big chunks (thankfully).

TPS checked out totally on a sweep test. The start position number was dead on.

Some on another (RS 2.5 Forum) have suggested maybe a leaking injector - but

1. Wouldnt that affect more than start
2. How would I know if thats the issue?

If you had a leaky injector, you'd blow carbon for a bit if and when it did fire. You'd probably have a carbon-coated plug as well. You'd have to do a pressure test on the pressure side of the fuel pump. It should maintain pressure after it stops if the injectors are all good.

Jon is correct, but the injectors are not the only possible cause of a failure of 'reserve pressure'. A bad check valve at the fuel pump, a bad cold start valve (if any), a leaky warm-up regulator, and (of course) any leaks in the fuel lines will also cause problems with this kind of effects.

Had an old grouchy ex-military guy that hung around a shop I was at.
I'd be troubleshooting a squawk, and he would saunter by, wearing an old derby,
and he would say in a John Wayne voice, "Check Yer Grounds Got Dammitt".
May not be relevant, but it sounded good...:noidea:

Thanks guys.

As regards grounds - why would she run 5x5 on all the numbers and performance once started if the ground was bad? I also have three grounds to the frame and engine just to make sure there is redundancy.

The thing is - once she is primed, starts and runs.

Without prime - nothing.

Before I go chasing changing sensors, I thought maybe someone could point me in a specific direction.

BTW how does one check if the pressure regulator is good or bad?

Leaks in the fuel lines would result in fuel smell somewhere - no? She is not leaking anywhere.

This is driving me nuts.

You can get a coolant temp sensor for about $20, it is one of the few things that will cause your problem. If the coolant temp wires are bare and touching somewhere in the harness it will cause the same problem.

If you think it is fuel pressure related install a fuel pressure gauge before the regulator and watch it when the pump is running and see where the pressure levels off and maintains a constant pressure. Turn the pump off and see if it holds pressure. I don't know if the factory regulator will keep the system pressurized after the pump is turned off. My aeromotive regulator does not keep the system pressurized with the pump off but it does maintain 40 psi with the engine idling and 48-50 psi while hovering depending on manifold pressure.

If you think you have a leaking injector just pull the injectors out of the manifold with them still attached to the rail and all fuel lines still attached. Turn the fuel pump on and pressurize the system and see if one is leaking from the nozzle, if you are going to replace one you might as well replace all of them if they are all the same age. While performing the leak check you could also go ahead and time the flow of the injectors to make sure they are all flowing the same. My factory injectors are each flowing 4.3 gph at 50 psi.

Try switching out your MAP(manifold air pressure sensor) with the one from your other engine before doing anything else more expensive.

Two years ago my engine started getting hard to start when it was warm. Then it just refused to fire consistently any more. $700 in various different sensors, coils, and a new starter, it turned out to be the MAP sensor. Plugged a spare in, and the engine ran like it had never missed a lick. If I had found the MAP sensor first, instead of last, would have saved myself the big bucks, and two months of frustration.

Not guaranteeing that's the culprit, but it's worth a shot.

This may sound like an odd point in the discussion to mention this, but the computer should be throwing out a code that will point directly to the culprit. Most of us don't wire for these, but it isn't difficult to wire up a reader if you have the schematic.

Jon,

In my case, I paid a Subaru mechanic to come out, with a Sub diagnostic tool, to see if he could figure out what the heck was going on. Even the Sub tool did not show that the MAP sensor was malfunctioning.

I had already bought a cheap code reader, and plugged it into the harness, prior to the mechanic showing up. The only codes shown were the same ones that always show up when I use a reader, all related to items no longer in the harness.