manofthefield

Fair warning: I’m going to include the car’s history from the last three years. The basics are that the car was running and had an issue that felt to me like fuel starvation, and now it dies immediately after starting ( ).

The car has roughly 55k miles had been stored for ~20 years. It went through two owners more recently that got it back on the road before I bought it. I’ve had it about three years. Everything was fine as far as I knew, though I think it burns more oil than it should on startup, but no big deal. It’s stock, though does have some aftermarket replacement parts (maybe exhaust, fuel pump…). I’m guessing I’ve put about 5000 miles on it driving around, driving to work and autocrossing.

There is an ongoing issue of vacuum building up in the gas tank especially when low on fuel; this causes fuel starvation at high RPMs. When I experienced this, I could stop, crack the gas cap and let it pressurize, then the problem would go away. This past fall I was at an autocross when I started experiencing this loss of power and assumed it was vacuum in the tank again. I cracked the gas cap between runs, but continued to have problems. On my 40 minute trip home on the highway I continued to experience the problem and I could tell I had no additional power at 70mph. I could maintain speed but had no acceleration. Again, it felt to me like fuel starvation. I drove it once or twice more in the fall before I stored the car for winter (change oil, Sta-bil in the fuel, fogging oil in the intake, remove battery) and of course was still having stumbling at high RPMs.

I changed the fuel filter, then put the car back on the road this spring experiencing the same trouble. The last time I was out it got progressively worse, to a point where I could only get to maybe 3k RPM in first and second would just “bog” unless I just barely touched the accelerator. I finally gathered some tools to start doing diagnostics.

I’ve tested fuel pressure and flow, which both look good. I was about to check the resistance on the coils, but then I wasn’t able to get the car running to get the coil up to temp per the FSM. It starts consistently, but dies after 1 or 2 seconds. Pressing the accelerator (giving it some gas) after it starts results in coughing and it still dies out (see video).

Coil resistance at ambient temp looks to be about .9 ohms, which the Haynes manual says is right, if I’m reading it correctly. I’m waiting for a second set of hands to test things like spark. Speaking of, I changed the spark plugs at some point in the fall (first time I had changed them) and noticed that the trailing plugs were pretty well deteriorated. I’m not sure if this is normal or not. The new plugs still look okay.

What should I be checking? Obviously easy things first. I keep saying this feels like fuel starvation, but know it could also be ignition related or maybe even something plugged in the exhaust. I’m hoping it’s not the fuel injectors, because they look like a pain to get to, but it looks like that could be a possibility.

diabolical1

iTrader: (3)

so does it still have the stock cat?

atheadwins

iTrader: (3)

Subscribed, I had almost the exact same issue. I have since replaced the entire fuel system except for the injectors, ran SS -an lines all the way from a fuel cell to the fuel rail and installed a new pressure regulator.

Everyone told me over and over there is no vapor lock on a EFI car and there is no way this could be happening. Yet it did. Especially on hot days.

I think our common issue here is the long term storage, possibly something was allowed to build up in the fuel lines during such long time periods. The car would run fine until warm up making me think there was just enough fuel but once warmed up under WOT it would stutter.

Good luck to you finding this I think it is a fuel issue. Once I get my car running I'll let you know how the full replacement went and if it solved the issue.

atheadwins

iTrader: (3)

Could be on to something here though, if it has the cat removed your stutter may be from the six-ports or auxiliary ports not opening because they don't have enough pressure.

manofthefield

There is a cat, and to me it looks like it is probably aftermarket. This was done before I purchased it and hasn't changed in the past three years. Car was running well with no known problems the first year or two I had it. Because I'm new to rotaries and the aux port, I don't know if it was operating correctly or not. And before it stopped running, it was much more than a stumble, it fell flat on its face.

LongDuck

Inoperative '6'-ports won't prevent the engine from starting, as they only open under 2-4psi of exhaust backpressure which is only generated under heavy throttle.

That Cat is aftermarket, and it could be clogged enough that it won't allow exhaust gas to flow past, in which case you're pressure stalling the engine. An easy test would be to disconnect the exhaust where it enters the Cat and move the car outside, get a fire extinguisher handy, and try to start the car. If it starts and runs - you'll know it because it will wake the dead! - then turn the engine off and replace the Cat, as that proves it's clogged. Some guys without emissions testing will just ram a steel rod (rebar) down the cat and break up the catalyst, effectively opening up the exhaust path, but this will increase noise considerably and then the car won't pass emissions testing, obviously.

The only other thing that jumps to mind is to check your Trailing coil lead which determines the signal for the ECU to fire the EFI - this is a white wire coming from one of the spade posts on the Trailing coil at the driver's fender, and also the ignitors themselves. An easy check on ignitor function is to swap leading and trailing ignitors on the distributor and see if it changes the condition - the engine won't start on Trailing ignition only, and swapping them potentially moves a good ignitor into a Leading position which allows it to start and run. If yes, your leading ignitor is bad (*which you just moved to trailing position!). If not, chances are both ignitors are good.

Since the car seems to fire for at least a moment during startup (enough to get the engine spinning), this sounds more like a fuel or exhaust issue - and you've already done the standard fuel filter replacement. Aside from that, the fuel pump might be to blame - but they tend to go out suddenly, not over time gradually. On that pump, I'd check the fuse (replace it, even if it looks good), check the power leads to the fuel pump in the storage bin behind the driver, as well as the connections on the external pump itself just in front of the tank after you remove the ding shield. A high resistance connection could keep the pump from drawing enough power to get solid pressure. It could be that you have enough static pressure when the engine first starts, but when more fuel is demanded, the pump can't provide any more pressure and then you effectively run your injectors out of gas.

Have a look at those things and report back - I'm sure we can get it nailed down. Good luck,

manofthefield

Good suggestions, I'll probably look into those this evening.

Fuel pump seems to be good; it runs, has good pressure, and flow when jumpered to run at the connector by the air box. My only other thought there is maybe the relay or other wiring is faulty.

Edit: reread your comments on wiring to the fuel pump, I will take a closer look at that stuff too

manofthefield

Short story is it's now running and I'm still not sure what was wrong.

I tried "manually" running the fuel pump by jumping the test connector while starting the car. I was thinking this would bypass the pump relay. No difference.

I disconnected the flange in front of the cat, no difference.

Using a timing light, I checked for spark on all four plug wires. All were good.

I'm not sure I got this right... LongDuck said "swap leading and trailing ignitors on the distributor," I swapped the coil to distributor wires with no difference.

Pulled the rubber air intake tube off the intake throttle body (correct name?) and sprayed gas in with a spray bottle. This was assuming the injectors were not working properly. No difference. I did note that the hose clamp on the airbox end of the rubber hose was loose and correctly tightened that when I re-installed the hose.

As another check for fuel, I disconnected the coil wires and turned the car over for about 20 seconds. Then I pulled the plugs to see if they were wet. Both trailing (top) plugs were wet, leading 1 (lower front) was damp and leading 2 (lower rear) was dry. So getting fuel, but seemed odd to me that the lower plugs were not as wet (or dry).

Dried the plugs and put everything back together. Figured "what the hell" and tried to start it again. It started, pretty roughly, probably because it was still partially flooded. But kept running and ran more smoothly. After 20 or 30 seconds I gave it some gas and revved to 2k RPM no problem. Let it idle for a few minutes while cleaning up and went for a test drive. After warming up, I ran up to 7k with no hiccups.

So I'm dumbfounded and a little concerned, but happy it's running again too. Time will tell, but I'm guessing I will still get vacuum in the tank when it's close to empty.

dnt 2.5

Are you sure that you have the fuel lines hooked up properly from the gas tank? My S had the same problem, and it turned out the previous owner had connected the gas lines incorrectly, and the fuel pump was trying to suck from the return line.

LongDuck

Actually, what I suggested was to rule out a bad ignitor by swapping the 2 that are on there for position. In other words, take both off and put them where the other one went. This could get you leading spark which will run the car when trailing spark alone, won't.

Also, your comment about the amount of gas on the plugs - remember that the plug holes aren't the same size for leading/trailing such that one will have a little tiny hole with very little chance for gas to get the plugs wet. That would be leading (bottom). Trailing holes (top) are bigger because they only get a fleeting shot at the A/F mixture as it's whizzing past being pushed by the rotor.

The biggest thing - is that it's running well now! Enjoy it,

sir revalot

Are you sure? Pretty sure trailing hole (top) is the small one.

Less chance for fuel to run away. I reckon.