At idle the car is missing bad I can push the throttle and it runs great but missing bad at idle my vacuum is at 10 which I know is really low when I put the timming light on the wire I see when it missing on cylinder does anyone know what what will cause this I have new wires and plugs but the plugs probly bad now since the missing fireing but what will cause the wires to cut out at idle I can pull the wire off the cap and see a good spark from the cap to wire could the wires be bad already had about 3 month

 

Well first thing id do is clean the IAC with some tb cleaner/seafoam.

You can also use the tb/carb cleaner/seafoam to find vacc leaks. Spray all around where you could have a leak- vacc lines, gaskets, ect., and if the ide is affected you have a leak there. I personnaly would start by fixing the vacc leaks and going from there, vacc leaks could be causing the problem and hinder performance and economy.

Ses light on?

Did you say you can tell with the timing light that theres a cyl that is not firing at all?

 

No light on have all vacuum leaks fixed checked this morning for any leaks don't have any I changed the cap and rotor out and it has new plugs it only does it bad at idle with the Roma around 2000 I heard miss fire I put my timing light on all the wires and found it skipping on 2 and 7 only and this is at both idle and 2000 do you know what would cause this to happen

 

The car is not fireing all the time at the distributor rePlaced the cap and rotor and still does it

 

How old are the plugs in it? Old bad plugs will definally cause a mis. The distributors them selves are prone to failure in these cars.

 

It's happing before it gets to the plug it's happing at the cap

 

Then its probably the pickup coil or the ignition control module in the distributor. When my dist. took a dump I picked one up from the local wrecking yard. I think it cost me around $40.00 for it.

 

I took ignition control module to parts store and tested it 3 times and it came out good going to change the coil tomorrow but it has a new distributor in car so pick up coil is still good and magnetized so I know thats not it is there a body ground for the coil/ignition system somewhere

 

Is the motor smooth at idle or is it shaking?
How do you know its misfiring?
Just by a timing light thats not flashing all the time?
Is the tach jumpy?

 

All of the above just used the timing light as a spark checker tach at 1000 and surgeing down to 400 engine shakeing piping in exhaust can take a plug wire off the car and put it close enough to the cap to see the spark and it will spark for a min then miss and it does it thru all the wires also used a spark tester after the timing light to double check and it done the same thing the timming light and the wires off the cap would spark for a min then quit then go back to sparking since I tested the icm and changed cap and rotor the coil is all that's left

 

I would change out the coil for sure, for good measure. I would also check the spark plug wires to make sure they didn't get crispy in any areas.

Did you ever clean your IAC? It's just a good idea to clean the carbon buildup off of this part, and it's easy to do.

 

It's all new iac tps map air intake it just not getting spark

 

This article will walk you step bye step. Often icm test out good but are faulty. It is wise to change the pickup coil and icm at the same time.

http://easyautodiagnostics.com/gm_ic...n_module_1.php

 

Well that artical has a lot of great stuff in it but it also says you can take it to a parts store and test it but I've tested it on car like it says and it passed so I took to Oreillys to have them double check it it passed 3 times there and I got a new cap and rotor while I was there I'll change coil tomorrow and let you know if changes if any

 

Put coil on my truck 91 Chevy 350 tbi and it ran fine so think ruled coil out

 

I have seen a severely cracked in the pole cause a miss. you other statement said im not getting spark so it was confusing. if the tbi truck as the small bas distributor throw that in and see what you have.

 

Do a compression check on every cylinder. Could be a burnt exhaust valve.

 

I'm not getting spark all the time it's intermediate the car will crank and run but will miss on all cylinders randomly going to change the coil out with the wires and clean the plugs and go from there that way I can rule out whole distributor system that all that's left changed the cap and rotor and distributor and still does it and compression is great it's a new motor with about 100 miles on it

 

Well are the valves properly adjusted??
rings don't always seat like they should. Don't assume that since its a new motor the rings all seated properly. (**it happens sometimes)

 

Well are the valves properly adjusted??
rings don't always seat like they should. Don't assume that since its a new motor the rings all seated properly. (**it happens sometimes)

 

150 compression it quit missing but I have the rpm at idle at 1000 but my vaccum is steady at 16 the motor that's at 10 btdc on timing which is high because was suppose to be at 6 btdc but the motor is bored .030 over with flat top pistons and a lunati cam

 

Did u replace the pickup coil that inside the distributor? My had a misfire and it ended up being the plug wires and I replaced them twice and did the same thing untill I bought a good set from MSD. I also replaced the distributor with a new MSD unit and the car has never run better!

 

Would a larger cam cause low vacuum?

 

big duration high lift cam doesn't generate much manifold vacuum.

What came are you using I thought you said you had a loss of spark

 

I don't remember what cam I bought I bought it back in 2006 and can't find the receipt for it. And I have no ideal how to find the lift once installed and I am lOsing spark at low idle about 700-800 rpm but when I raise the idle to 1000-1100 it seems stop missing sorry if confused you been outside in sun for a week trying to figure out why it's doing it at low idle

 

Im just going to buy a msd coil to get a more powerful spark since the spark is weak at low idle and misses when it where it's suppose to be at 700rpm

 

it takes more kv to fire a spark plug at a higher rpm. A stock acdelco coil will put out up to 45kv use a spark tester to test your coil

 

Swap the misfiring cylinders spark plug with another and see if the misfire changes with the swap. This way you can tell if it is the spark plug or something else. Also they're could be dirt blocking the fuel rail causing it to misfire, so when you give it gas increasing pressure the dirt my be pushed away from blocking the injector and stop the misfiring.

 

It has new injectors and cleaned the fuel system the spark is shorting out weak I have a inline spark tester with little light and at low Rpms around 600-800 it missing spark everyonce and a while on every cylinder but when I bring the car idle screw up to 1000 rpm it runs alot better