i didnt check the exact rpms, but it would seem so.

 

I know how frustrating this is M90, but I also feel this is something easy to fix once found. It's probably going to be a face-palm type repair, like "I can't believe this caused all that trouble"!

 

heres the problem. the engine isnt drawing enough vacuum to calculate fuel correctly, (about 15in/hg) so when you you get it to run ok, and plug the ECU in it starts adding fuel to make up for the decrease in vacuum, which in turn causes the vacuum level to drop, which causes more fuel to be added, and less vacuum and more fuel and less vacuum until the engine is barely running.

its a vicious cycle.

whoever figures out how to get the vacuum from 15in/hg to 25 in/hg wins.

 

If the engine is cold, the ECU will expect it to run above normal tickover rpm, but NOT as high as c.1400 rpm. At c.1400 rpm, on a closed throttle position sensor, the ECU thinks the car is on the over-run and cuts the fuel to the injectors. Just below 1400 rpm, it turns the injectors on again. This is the cause of the common hunting symptom that occurs when the AAV is stuck open (ie a vacuum leak in effect) and the car is still cold and ticking over.

May I suggest that you block off the throttles and see what happens if you start it. It will ether prove there is a vac leak and you have not found it, or that there is not. If you are sure there is one, it should be big enough to start the car and noisy enough to find!

Greg

Greg

 

Give keisler engineering a call about the transmission. Or use a gforce gearset in a t5. Believe me youll like how smooth the t5 shifts and how small it is more than anything else

 

I think Greg's right on the money with this one.

 

again. its not a vacuum leak. both throttle bodies totally closed and it dies.

while i was checking for vacuum leaks it started surging again after about a 5 minute run. again its like throwing a switch. it just happens out of nowhere without warning. between 300-1,000 rpm and not a rev higher. about 5 more minutes of that and it died on its own.

so about 10 minutes of tinkering and i cant get it started again.

 

I have to think on this for a bit.
Just out of curiosity, where do you have the vac line to the distributor attached? Just for giggles, disconnect and plug the line and see how it runs..

 

Here's what I was wondering: The vac advance on these cars is supposed to have a small leak, so they won't hold vacuum. I recall that you changed yours, and if you put in one that does not have the small leak, the moment the engine starts and creates vacuum, it will pull the advance, altering the timing and causing the engine idle to change. When the timing gets beyond a certain point it dies out, the vacuum is lost and timing returns to where the engine can run, causing the surging.

Maybe I'm way off, but it's worth a shot.

 

the engine has to cool down to be started again. back down to ~100* F

 

have you done a compression test,? just to see if cylinders are resonably close.

what if it has a dropped seat, and causing backfires, crazy fluctuating manifold pressures.

forum diagnosis can be to much information overload. personally, i would have to shut off all outside opinions, back away for couple days, and just let things ride for a while.

sounds like its making you cra%y, you cant think smoothly when you under PEER pressure!! young man.

 

have you checked your overrun valves?

 

no. i saw these in a schematic but didnt think much of them. what do they do?

 

allow extra air in when the throttles are closed, if one kept bouncing open the closed it could cause the symptoms of a bad vacuum leak like it sounds where its all bouncy and lopy

 

i cant find any pictures of it. can you bypass them?

 

Overrun valves are fine.

again. 5 minute warm up and then it shuts off like a switch, with no warning and no hesitation. it runs like **** with backfires during the first 5 minutes. there is no chance in hell of starting it once its shut off on its own until it cools back down.

 

question. i have a blue switch thats wired into the amp IIRC, and has a vacuum hose coming out of it. any chance this could be my issue?

is this the vacuum full load switch?

 

Sounds like the full load vacuum switch. You can verify this with the wiring diagram.

Have you verified every wire yet? Use a meter and wiring diagram and do the checks at ECU.

Have you done compression test yet? Do it properly. All plugs out, throttles held open. Battery charger on battery. Crank and stop after pressure stops building. Write down the numbers.

Do a leak down test too.

Have you fixed the AAV hoses and set throttle plates properly? If not you need to do that.

Have you verified fuel pressure yet?


I posted a list on the other post you made before you hijacked this one and you hadn't done half of the possible items. As I talked to you about make a list and work throughout the list. You are just randomly trying stuff and hoping for a silver bullet. The only way to fix this is to make a list of possibilities and one at a time check your items on the list. Obviously start with easy and work toward hardest. I posted a list on your other thread.

 

yes, ive checked the wiring harness. its fine.


so thats 4 things i havent done yet. so ive done a lot more than half the list.
and i posted the thing that i had done.

 

im more concerned with why it shuts off so abruptly. if you think its because of a compression leak, high fuel pressure, or that its not related to the way the engine runs then thats fine. im not buying it.