smg944

iTrader: (34)

ok got a turbo 2 fc (s4) that wont idle at all. the cars runs great boosts fine to .35 bar. smooth powerband but will not idle at all. i tried unpluging the bac to see if that was it and nothing. checked quickly through vac leaks but didnt find anything. once it goes below 1000rpms it is shutting off. i checked through the faq but i think its down because it came up with nothing on my searches.

here is the vid i took, i had my foot on the gas holding it around 1500 rpms, until the 57 second of the vid where i let off and it shut down as if i pulled the key out. any ideas would be great.

ultrataco

iTrader: (2)

I was going to start a new thread, but this (old) post describes my problem exactly, except I have an NA and have not yet checked the BAC, and my CEL comes on every time I lift off the gas pedal.
So, any thoughts?

89GXLer

This thread also sounds like the issue I'm having.


Car: 89 GXL NA 5spd

Symptom: Will start up well, runs through the high RPM cycle (~3K), will then idle (~1.5K at first and then slowly comes down to about 1K as it starts to warm up), runs for 3-4 minutes, and then just as it starts to warm up (right around 1k RPM) it just starts shutting down and it's hard to be stopped (burping the throttle will sometimes save it). Can't start after that and the engine floods - after cool down and clean out of flood it will start fine and then do it again.

I just rebuilt the engine (2 used rotors, 2 new housings, and an Atkins rebuild kit) but this issue existed before I started the rebuild (was stored in my garage up to this point) as it would do the same thing when it was only running on the rear rotor (front spat a seal and scored the rotor and the housing, had no compression at all, and thus thus the rebuild).

I assumed this issue was part of not running on 1 rotor but it's still happening.

Note that when it does start now, the engine runs absolutely great - never ran better since I bought it.

Things I've checked:

1) Fuel - I seem to have lots of fuel coming from the filter and the filter is not very old

2) Air filter is almost brand new

3) I have a brand new set of plugs in it as I started it first after the rebuild with the old plugs that were in it and was saving the new ones for after it blew out all the Vaseline and crap from the rebuild.

Plugs are nice and clean when you pull them.

Note: also new ignition wires were installed as part of the rebuild.

4) verified that the plugs are firing from each coil before and after it shuts down

5) I tried restarting it right away by using a spray bottle with gas and spraying it in the intake as I turned it over. Doesn't go.

6) I tried compressed air injected into the intake as I turned it over. Doesn't go.

I put a brand new set of Bonez cats and an exhaust system so there seems to be lots of flow out the back and they shouldn't be plugged up. The manifold was also clean inside when I put it back on.

I put a brand new oxygen sensor on it also as part of the rebuild.

Compression tests:

Front Rotor:
Cold: 30 psi
After it quits: 32 psi

Rear Rotor
Cold: 32 psi
After it quits: 33 psi

(all numbers are approximate and I was using a very old tester)

All bounces are completely even so it looks like my new apex seals are good.

I only checked one rotor for overall pressure (compression valve closed) and it only gave me just over 90 psi so that seems low but I'm hoping that's because it's never reached full operating temperature yet and hasn't been broken in yet.

I bought a clip on tester spark plug to see if it was shutting ignition down but found that it wasn't and that there was lots of spark.

Unfortunately I don't have a fuel pressure gauge to check the level of pressure before, during, and after for the injectors but I have one on order and should have it in a couple of days.

I can't find any vac leaks and I still have to double check the timing (set it to the same spot it had been before the rebuild and it seems to run really nice up until the 5 minutes).


I did some more playing around, started it, pulled the water temp sensor right away (ECU should have gone into a limp home mode (adjusts the map to normal operating temperature)) and it did change how it was running a bit but still stalled after about 5 minutes total of running.

Looks like the water temp sensor isn't my issue.


I also found that I can keep it running if I keep the engine over 2000 RPM (it runs great now since the rebuild). It seems to start to die somewhere around 1500 RPM or lower so it looks like it's definitely getting too much fuel and drowning itself.

My "assistant" (retired mechanic) and I sat and talked about what happened around the time this quitting issue started (before the rebuild).

Around that time, I tried to start the car one evening, the starter wouldn't role, and I was getting sparks around the ground wire from the firewall to the transmission bell housing.

I discovered the starter had been getting ground through it, it had melted off most of the insulation (it looked like it had been this way for quite a while) since it was too small to carry current for the starter, had burnt off, and this was all because someone previously working on the car had left the main engine ground off at the starter (not me).

This means it was hunting for ground in other spots on the car also. I haven't found any burned ones yet but am wondering if this has somehow messed up the ECU.

It did run fine a couple of other times (just ran it, didn't actually drive anywhere) after I replaced the burnt ground and put the main ground back on at the starter.

Any comments or thoughts from anybody?

Maybe the ECU is activating the secondary injectors when it's not supposed to? Maybe messed up the fuel map and it's giving too heavy a fuel supply for under 1500 RPM in the normal operating temperature range?

I do have a used ECU on its way but it hasn't arrived yet so I'll try that when it arrives.



Has anybody seen this before and figured it out? Does anybody know what it is? Can you suggest what to try next?

Any help would be appreciated.


Thanks

Grant

helghast7

iTrader: (6)

check sensors!!!!!!!!!!!!!!!!

sounds like symptom of a dead tps

ultrataco

iTrader: (2)

I tested my TPS and the only part out of spec is the full range closed. The narrow range closed was out of spec, but I adjusted a screw to fix it. I don't see any way to adjust the full range though.

helghast7

iTrader: (6)

do you have a friend that can swap tps with?

89GXLer

I swapped my TPS today with a know working one and it didn't make any difference.

I also swapped in a known working ECU out of another car and it didn't make a difference either.

I got my spare ECU and the car wouldn't even try to fire up at all so it's DOA.


Anybody got any more suggestions to try?


Thanks

Grant