Starts, revs, dies

[jakepkoe]

Just completed a motor swap. The thing starts, revs to 2k, then dies - maybe two seconds. I can keep it running by spraying starting fluid, so I'm sure it's a fuel issue. I have tried jumping the fuel pump to make it constantly run, but I get the same result. I've read where some folks with a similar problem can keep it running normally by keeping the key turned to the start position - no dice in my case. I'm going to pick up a fuel filter tomorrow and try that since it hasn't been changed since I've owned it (not many miles but 3-4 years) and the fuel tends to sit a while.

My car is a '94 and the donor is a '99. Using the '94 throttle body and other sensors. It has the non-US factory fuel pressure regulator. Will the '94 fuel pump produce the pressure the '99 injectors want? Even if not, I'd assume that it'd run - just maybe poorly? Any other suggestions? There are reports about issues with the AFM, I didn't do anything with it during the swap. I've unplugged and checked it but see no obvious problems. Any suggestions?

[OZMDD]

Check your fuel plumbing on the rail, might be reversed.

[jakepkoe]

Good call. When I read your suggestion I had a glimmer of embarrassed hope for having overlooked it. However, I've just confirmed it's plumbed correctly.

[trickyrix]

Are you using the '99 fuel rail and pressure regulator? FWIW, when I did the '99 head swap in my '94, I had to use the '99 fuel rail, BUT I had to fit the '94 regulator to the rail. IIRC, the '99 regulates the fuel pressure on the front end rather than the return side, if that makes sense.

Also, I'm assuming you're using the old '94 CAS instead of whatever the '99 engine uses. If you haven't done so, you'll need to use the old valve cover and remove the cover plate from behind the exhaust cam - the cam is still keyed for the old CAS.

Those are the only ideas I've got right now...

[jakepkoe]

I'm using the '94 CAS.

The '99 US motors apparently don't use a fuel pressure regulator, and are returnless. The one I bought has the non-US system that uses a vacuum operated fuel pressure regulator. I could still have it backwards though. I have the fuel return line coming out of the regulator and the supply coming in the other end. I'm assuming the regulator restricts flow to build pressure and should be at the end of the run. I don't see how it could give pressure to the injectors otherwise. I ran the lines just like they were on the '94.

[trickyrix]

Yep, the return line should come out of the regulator. Stupid question, but are you sure it's the return line? IIRC, the way the NB fuel rail sits, the pressure and return sides are opposite of the NA. It seems like we had to run new fuel lines to get the extra reach.

[OZMDD]

That's what I think also; they are often reversed when people do the swap. Take them off and run the pump to see which one delivers gas.

[chriscar]

Just looked at my car to confirm: The fuel line closest to the front of the car goes to the regulator, the rear line to the fuel rail.

C

[jakepkoe]

Yeah, I disconnected the rubber line from the hard line at the chassis and ran the fuel pump. Fuel came out of the rubber line from the regulator side. I'll try to source a fuel pressure gauge today and check that tonight. I will also try to check the signal at the injector. It seem that it's somehow losing fuel after the initial start. As if 'start' mode works but 'run' mode doesn't. I'm not sure how any of this is controlled at the computer.

When it starts and revs, it sounds completely normal. It's not revving wildly or anything, just sounds like the standard bump you get when you start a fuel injected car. I still have the fuel pump jumped, so I know that it is pumping fuel constantly when the key is on. I'm sure it's something simple I've overlooked. The old motor was running when pulled, and I'm using all of the electronic controls off the old motor except for the injectors, I think that may be the only 'new' electronic bit I'm using.

[chriscar]

"Fuel came out of the rubber line from the regulator side."

That's backwards. The feed should go to the rail, and the return goes to the regulator.

Remember:
Feed = Fuel Rail
Return = Regulator

C

[jakepkoe]

I wasn't clear. I disconnected the line from the regulator side at the chassis, and the fuel came from the regulator side, not the chassis side. So, the fuel is coming in the other end of the rail and out through the regulator. If it was backward I should see fuel coming from the chassis side of that line. The rubber line that showed fuel flow was hooked to the regulator on the other end, so the fuel is coming from the regulator.


Fuel is flowing from the pump to the back of the rail, through the rail to the regulator, and back to tank. If that's not right I'm happy to change it. I'd love for it to be that simple.

[jakepkoe]

Sorry for the last post, a little repetitive now that I read it again. Trying to say that I broke the connection on the return side instead of the supply side, and that the fuel is pouring out headed back to the tank as you'd expect.

I installed a pressure gauge in the feed side and it's showing 43 psi. When the engine starts the pressure drops to about 30 before it dies. Disconnecting the pressure regulator, the pressure stays pretty steady around 43, but it dies just the same.

[jakepkoe]

Checked the #4 injector since it's easy to reach. Resistance is 13.8 ohms. The signals are there too, with a test light anyway - it glows really dimly so long as the engine is running - I'm assuming it's dim because the pulses are short. If I keep it running with starting fluid it continues to glow. Double checked the pulse and while keeping it running with the spray, I'm seeing pulse frequency of about 24Hz. I have spark, fuel pressure, and injector pulse. Also have air, I can vary the rpm when running with the starting fluid by opening the butterfly. Unless the injectors are so plugged they're not flowing enough to keep it running, but that doesn't make sense since it starts and revs to 2k.

I've been double/triple checking the fuel hose routing. I have the fuel pressure gauge in the supply side line, so I'm sure that's actually it since it's showing pressure - After the regulator, the pressure should be much lower. After the pressure gauge, the line goes to the nipple behind the FPR in this pic: http://revlimiter.net/miata/images/eng_fuelrail.jpg I'm confident the fuel lines are correct - I'd swap them just to check and rule it out but I'm afraid of damaging the regulator.

I tried it with the MAF disconnected, but get the same thing. I've read that a bad coolant temp sensor can cause some crazy issues. The reason I replaced the motor is because I severely overheated the original one, I don't think it would have damaged the sensor but I'm grasping at straws now, looking for any/everything.

I currently have the EGR blocked off. I'd think this might throw a code, but shouldn't keep it from running.

[jakepkoe]

Figured I should update this in case anyone stumbles across it during a search later.

Checked the codes to find 1, 4, 8, 25. I had cranked it before with the CAS unplugged which must have generated the 4/8 codes. Cleared and checked again, and got 1 and 25. Searching on code 1 (IGF Signal) I found this thread, which was quite similar to my problem: http://forum.specmiata.com/cgi-bin/u...4;t=003654;p=0. Went and picked up a coil pack today and lo and behold it works. I never considered the coils as it would run as long as I was feeding it fuel. It's the only thing I changed, so it has to have been the problem. I gather that the coil sends some kind of signal back to the computer and that must be the part that is bad on my old coil pack. I'm going to go finish putting it back together (under tray and sway bar) and take it for a spin and see how it goes. Thanks to all who offered advice.

[OZMDD]

Good job.