M20B25 Start, Idle, die (RESOLVED)

[Denny]

Guys

Last 2 days been trying to diagnose this weird problem with my M20B25 engine.

I was tuning it and it was running fine...then when I approached a light and pressed on the clutch and brake the car would stall (but restarted right away) did it about 5 times so I drove back home and let her sit for the night.

The next day (cold start)

1.car cranks over,
2.engine catches/starts
3. idles (goes from 700rpm-1500rpm...down to 600rpm-1200rpm and then down to 400rpm-800rpm and finally dies down (idles for about 5-6 seconds total)

Now If I try again right after it only idles (2-3 seconds) dies right after.

Troubleshooting so far.

1. Compression on cylinders (150,145,145,150,150,150) so am good here actually surprised I sent over 13PSI on this engine
2. Checked for air leaks
3. Sparkplugs are wet with fuel
4. Spark is present as car starts

What would you check at this point? any help is greatly appreciated.

**When I resolve this I will document this to be able to help others.

[Just Scott]

Check more for vacuum leaks - had a similar issue and fixed it by replacing the vacuum line between the intake manifold and the fuel pressure regulator.

Pressing the brake, makes me think vacuum of some sort since the booster is vacuum assist.

But honestly, I'm just guessing. The Bentleys can walk you through this probably.

[Denny]

Check more for vacuum leaks - had a similar issue and fixed it by replacing the vacuum line between the intake manifold and the fuel pressure regulator.

Pressing the brake, makes me think vacuum of some sort since the booster is vacuum assist.

But honestly, I'm just guessing. The Bentleys can walk you through this probably.

Im going to check even more for vaccum leaks...

It stalls out when I press on the clutch to come to a stop sorry for confusing with the braking... like it cant return to idle.

Engine warm will restart and idle and cold will start but not keep an idle.

I got the book just looking for real live experience

[jlevie]

The first thing to rule out would be intake leaks. Have a shop run a smoke test.

[Denny]

The first thing to rule out would be intake leaks. Have a shop run a smoke test.

Thanks, but I dont want to pay 300$ to get my car towed to a shop as right now I cant drive it. Any tips tricks on a cheap way I could test for leaks by doing a smoke test at home? I checked visually for leaks but I know thats not very effective..

[jlevie]

The only way you can do a smoke test is with a smoke machine. The cheapest off the shelf machines are about $1000. There are some articles on the web about how to make a machine that will work. As a guess I'd say you could build one for about $100 that would get the job done.

[Denny]

The only way you can do a smoke test is with a smoke machine. The cheapest off the shelf machines are about $1000. There are some articles on the web about how to make a machine that will work. As a guess I'd say you could build one for about $100 that would get the job done.

thanks man appreciate it. You got me motivated to build one, NA or not since am always going to be forced inducted this tool am sure will be useful in the future too.... no room for any air leaks.

One quick google search and check this out:

http://www.fiero.nl/forum/Forum1/HTML/081547.html

[Denny]

Well tonight I did some more testing on the car (while I build a air leak tester)

1.Crank over
2.Start
3. idles (goes from 700rpm-1500rpm...down to 600rpm-1200rpm and then down to 400rpm-800rpm and finally dies down (idles for about 5-6 seconds total)
4. Crank again same results but idle lasts 2 seconds
5.crank again and no more start exept this time i try to give it gas and my vaccum gauge/boost goes to 3-4psi?!? and back down to 0 vaccum and dies

now am sure the car is flooded with fuel... :(

things checked tonight:

1. Coil is good
2. wires, rotors, dist and Coolant temp sensor all good

I looked over again everywhere and cant find leaks...

According to this anybody know if this could still be a vaccum leak? or is this pointing to something in particular?

[dnguyen1963]

search www.scottykilmer.com for cigar smoke test.

[Denny]

search www.scottykilmer.com for cigar smoke test.

thanks man. that guy Scotty is funny lol... the cigar trick is a pretty cheap alternative.

I gave it a shot and no leaks... :(

I hope I dont have to pull the 30# injectors (now am wondering thsi all happen when I went for a ride and hit 13PSI) did I hit max dutycycle and one or all of the injectors stayed open? what are the odds?

[Denny]

****RESOLVED!!****



I GOT Fire....I GOT Fuel.... Give me a better 12+V connection for my MILLER MAF LOL...

I had used those pesky little blue connectors to splice in 12+ grey wire to the big blue/red wire in the ECU plug for my MILLER MAF and with time it disconnected slightly to give me days and days of headaches...

Over and out! thanks to those that took time to help. Hope this helps others