350 diagnostic help-- stumble stall when warm

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jfz80

jfz80

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90% of the time when something is wrong with a Gen II small block something is going on with that. It can cut in and out. The coil is the number one problem with them.
 
How would you quantify or check spark?

Its there and is the main supsected culprit. Marhsalls recommendation to strap the light on the hood and go for a ride was a good one. I am separated from the vehicle and making a list and game plan to return.

Coil is new. Did not have it tested at purchase time.
 
jfz80 said:
How would you quantify or check spark?

Its there and is the main supsected culprit. Marhsalls recommendation to strap the light on the hood and go for a ride was a good one. I am separated from the vehicle and making a list and game plan to return.

Coil is new. Did not have it tested at purchase time.
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It's kind of hard to check for something like that really. I would buy a new one for the time being (different brand) and see that that helps. Coils for these engines, even "performance coils" can go bad easily. Try an MSD one. I had one that wouldn't perform well on start up but the car ran flawlessly up to 6500RPM when started. I replaced wires and the starter before I figured it out. Another that my friend had had no problem starting but after it warmed up it would go bad.
 
The replacement fuel pump was the wrong one (only did 5-9psi). Jason swapped it out with another and took off up the road. seemd like it was running fine when he left. :steer:
 
If it's still acting up, my neighbor who is a Chevy guy, suggested checking the coil and ignition control module on the distributor.
 
Unfortunately for Jason, there probably isn't much more to replace.

One thing I forgot to ask, were y'all able to check any codes? Seems like a good idea to find the wire and get a check engine light hooked up before it's needed again.
 
10- 4 and a big thank you to all that helped.
Sorry I was not able to update sooner as I just got back in from Raleigh this morning.

Will be adding a check engine light in line for future use. ECM and coil are new.

New fuel pump 17-22 psi and away she went. The loping idle (up/down/up/down) returned as soon as I got off the highway and it produced a small stumble/miss under load but is driveable and the conditions can be avoided by careful accelleration.
 
If you bought a new MAP sensor put the old one back in. I'm willing to bet the looping will go away. Those symptoms sound like that sensor.
 
Trollhole said:
If you bought a new MAP sensor put the old one back in. I'm willing to bet the looping will go away. Those symptoms sound like that sensor.
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x2:cheers:
 
hey, I think thats the one part I DIDNT buy. but maybe its time ?

from reading this am I was coming across MAP (esp if it gets wet through hood) and IAC
 
looping can be caused by the engine wanting to die. The revving back up is the stall compensator kicking in. What you need to look for is why it's stalling. It's usually due to timing, or a sensor giving the ECU the wrong info.
 
Trollhole said:
looping can be caused by the engine wanting to die. The revving back up is the stall compensator kicking in. What you need to look for is why it's stalling. It's usually due to timing, or a sensor giving the ECU the wrong info.
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These could also be due to unmetered air coming in or as stated before the coil.
 
One thing I believe that was discussed is the spacer tube between the air filter and the throttle body. I think Jason's is plastic and believe the stock part is metal. I would assume an air leak there could cause problems. Maybe it's worth trying a replacement temporarily, or adding a better gasket for sealing.
 
strong_toy said:
One thing I believe that was discussed is the spacer tube between the air filter and the throttle body. I think Jason's is plastic and believe the stock part is metal. I would assume an air leak there could cause problems. Maybe it's worth trying a replacement temporarily, or adding a better gasket for sealing.
Click to expand...

good point
 
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