'91 t2 won't stay running...
 

Ok, so RoXanne is having some troubles.

First:
Normally she has a bit of trouble starting the first time of the day, but a little nursing and feathering of the gas and everything's fine. She purrs along just like she's always done.

Yesterday morning, I tried to start and instead of the warbling rumble she normally starts up with, it was a harsher growling noise, and she wouldn't stay running. Just turning the key was a short "start-growl-die". Key plus a small (20%) push on the gas gave a "start-growl-growl-die". And finally turning the key and then tromping on the gas got "start-growl-growl-growl-die" as a result.

Fuel pressure showing normal, no massive raw fuel smell, everything seems to be functioning normally with the exception of the engine not remaining running.

Secondly:
This might be related, I don't know.

When the engine is warmed up and running normally, a light press (not much more than the weight of my foot on the accelerator) will cause the RPMs to drop drastically. If I don't either remove my foot immediately or press harder, I can kill the engine.

Basically:
0% = idle
1-10% = engine dies
11-100% = RPMs increase normally.

Third:
Also possibly related.

When cruising in 4th or 5th, 65-75mph, RPMs in the mid 3s to low 4s, my narrowband AFR gauge will suddenly drop from it's normal reading on the rich side of the rich/stoich line down to WAY lean, accompanied by sound of the engine "Stumbling" or "hesitating" I'm not sure how to describe it. Maybe "struggling" would be the best term.

I've been watching the fuel percentages on my SDS, and when that happens, the fuel amount going to the engine remains steady, my manifold pressure remains steady, etc, etc.

It sounds and feels like the fuel cuts out, so if I wasn't seeing my instruments tell me otherwise, that would have been my diagnosis.

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So those are my three issues, they may all be related, maybe not.

I really need some help, as RoXanne is my DD, and I'll confess to not being that engie-savvy, so I'm not even sure where to start looking to find problems.

Thanks in advance!

Update: Just went outside and tried to start her again (first time today)

Same symptoms, "start-growl-die" with the growling of various lengths depending on my application of the accelerator.

I actually managed to get her warmed up, but I had to keep the RPMs above 2500.

New symptom: While @ ~2500 RPM the fuel seems to cut out and the RPM drop drastically, if I goose the accelerator, the engine "growl-pop!" and then runs normally for a bit, then the cycle starts over again. The pop isn't quite a backfire but it's definitely an audible pop.

After a few minutes of this, just as the temp sensor crossed into optimal operating range, the RPMs dropped again, I goosed the pedal, and... nothing. While I was still getting resistance from the pedal, the engine didn't respond to the added fuel and died. I was watching my SDS the whole time and the fuel delivery increased in response to me pressing the pedal.

Now the car won't start at all, just turns over continually without catching.

I stopped trying, because I didn't want to burn the starter out.

Now I'm really worried, because I have no idea what to do.

sounds like it could be a tps problem

Sounds like the fuel pump took a dive, can you verify fuel pressure?

I don't have a secondary gauge to use to check...all I've got is the pillar-installed fuel pressure gauge, which shows a normal linear increase in pressure with the position of the throttle, then spikes up in pressure a bit as the RPMs drop and the engine is about to die, then settles back to base pressure when the engine is off.

For reference, fuel pressure gauge reads ~40 when car is off, ~60 when starting and then between ~45 and ~60 when car is on, depending on throttle position.

Shown pressure increase while RPMs are dropping and engine is dying is ~5

On my NA s4 I had a very similar problem. After describing the problem to my friend/shop neighbor Paul (owner of http://www.rotorsport2.com/ ) he walked to his work bench, grabbed an old thermo switch he had lying around and threw it to me. Replaced the thermo switch with the one he kicked down, problem solved. It is the switch that is located below the alternator plugged into the thermostat housing. Not sure if it is the same on your TII S5 motor.

Not sure if a bad thermo switch could cause this on startup, but hey, it's a cheaper fix to attempt than replacing a fuel pump for $270

Anyone else have any suggestions of something to try?

Sorry for the late response, I've been super busy. Is everything still as described above?

Steve

can i have a pic of the thermo switch please? installed and uninstalled

really sounds like a bad tps, check it with an OHM METER should read 1k idle, or no trottle if you have the cold start assist removed, and 5k ohm full thottle, sounds like it's not reading right down low.

1. Pull trouble codes
2. Check closed-loop emissions operation
3. Check spark present at all 4 high tension leads
4. Check timing
5. Check operation of double throttle diagram
6. Check operation of bypass air valve
7. Check for vacuum leaks
8. Check condition of spark plugs
9. Check O2 sensor voltage

Procedures in FSM

When was the last time...

...the fuel injectors were cleaned?
...the O2 sensor was replaced?

Both of these are 30k mile items, and either one could cause the problems

Check also TPS operation for flat spots/dropouts using an analog ohmmeter

Check mass airflow sensor for the same

Boost sensor

Air pressure sensor

...?

FYI... (not trying to be a dick at all)
1.The SDS doesn't have diagnostic capabilities.
2.Closed loop is only used at predetermined levels of vacuum.
4.Please don't move the timing unless it appears to have moved by itself.
6.It doesn't have a BAV.
9.The SDS doesn't change its mixture based on o2 reading unless its in closed loop.

Good info though.

Is this still going on Isaac?

Check if the SDS is showing accurate TPS readings on the TPS page. The TPS probably wouldn't be causing this. I still think it's a vacuum leak...

Lacking information to the contrary, I was assuming the problem car was equipped with a stock ECU. Is the SDS an aftermarket control unit? His symptoms sure sound like a lean misfire due to insufiicient fuel or excess (unmetered) air.

Ok update.

@calpatriot: SDS is aftermarket fuel controller. My AFR gauge is showing Stoich to Rich readings until the engine starts to die.

@OTT: Yeah, everything is still the same. Talked to some local guys at the Mazda dealership, some of the old master techs, and their suggestions were to check with a timing light to make sure my coils are still good, and if so, they would let me use their rotary compression tester to check compression.

Their diagnosis is either bad coil(s) or no compression (blown engine).

Either way, we'll see

Here's to hoping its the coils, and not the compression.

Quick question - when was the last time you changed your fuel filter?

The part about giving it slight throttle + dying sounds like not enough fuel. I had a somewhat similar problem, pulled my fuel filter to watch chunks of rust fall from the intake side of it. Slapped a new one on + it ran awesome.

I'm going to replace that anyway, but I need to procure a timing light and possibly a compression tester first to check that all out. No sense buying a $30 fuel filter when I might have to drop $2k on a new engine...

Best deal on a timing light may be the Harbor Freight one for $16. Mine works great...

They also have a little $3 spark tester which should show you with a no-light condition if you have a failed coil...

Supposedly you can test the compression with a conventional tester (though there is a specialized one) but you have to watch the 'bounces' of the needle pretty closely. The peaks are supposed to be over 85 lbs. I have not tried this yet... perhaps someone else will have...

Fuel pressure is a possibility, but seems unlikely if you AFR is reading OK right up to the problem, but it is not hard to check. $30 will get you a good fuel pressure guage kit with all the connectors you need. If the fuel filter were the problem, I would expect the fuel pressure to fall off at some rpm, but it would seem you should see that on the AFR if it were happening.

Vacuum Leak? My car behaved the exact same way when I blew the tube between the Idle air control valve and the charge pipe off.
Compression is easy to test.just pull the egi fuse and then pull the front leading spark plug, stick your finger in front of the hole and have someone crank the car. You should feel and hear a lot of air movement like this" pshh,pshh,pshh,pshh,pshh etc." the replace the front leading plug and do the same for the back. You'll be able to tell if you have a compression problem. I'm gonna say you've got a big leak in the charge system somewhere. Stock TMIC or FMIC?

I'll check out HF, I've got one near my work.

That was my thought exactly.

I've already done the finger trick to check compression and I -am- feeling pressure, but talking to a Mazda master tech he said that the difference between a good engine and a blown one is 150 vs 120, which he said can be barely felt physically.

I'll check all the vac tubes again, maybe just replace the lot of them for the hell of it.