[85silvereldo]

changed evap purge valve on top of engine, changed vent valve by canister so what else. no miss except at idle and off idle until moving then smooth , HELP

 

[Submariner409]

What car, what engine, what year ??? Are we working on a Cadillac of some vintage or on a Caterpillar bucket loader ? Any diagnostic codes set in the car's DTC system ?

Please update your profile so that your username banner looks like those of other members. Thanks.

(Even within this Deville year group forum there are several models and engines possible)

 

[85silvereldo]

99 base deville northstar v8

also now missing while driving with light or any load on engine like accel or hills

 

[Ranger]

How old are the plugs & wires?
Have you checked for vacuum leaks?
When was the TB last cleaned?
Have you checked fuel pressure?

 

[Submariner409]

99 base deville

OK - I'll update your profile for you............:gah:

As posted - plugs, wires, coils, ICM cleaning, ICM ground cable check, vacuum leaks checks, PCV system checks.

 

[rodnok01]

What the others have said, tb, plugs, wires, pcm ground. Vac hoses and ends(check them), i used a couple clamps on mine.
Snug the intake bolts down also.
If you have access to handheld scanner it may point to cyl missing if any and number of misfires.

 

[sefiro]

Also, check plenum. Had the same symptom on 02 Seville with a small hole in the plenum.

 

[85silvereldo]

update: fuel press in spec, changed plugs, no vac leaks, constant 15 vac, fuel regulator checked good, wires, coils all within specs. cured miss for week maybe but now have po603 code not there before so how to deal with it. see new post today

 

[rodnok01]

Have you determined which if any cylinder is showing misfires? I had a weird issue bite me few months ago, plug wire end(coil end) had missing clip to keep wire snapped down and I'd get a random misfire for the last year almost. It would come and go and didn't show misfires until it ate that coil. Baffled me for long time as it was it very seldom occurred. Anyway good luck...

 

[85silvereldo]

i will check wires/coil connection thanks

 

[jmf1964]

Have you done a block test to check for combustion gasses in the coolant ?

 

[85silvereldo]

how do you do a block test? had miss on #7 and 8, plugs had oil on them, cleaned and ran much better but decided to replace all 8 plugs

 

[Submariner409]

Cylinder block exhaust gas test - checks the airspace in the surge tank for presence of exhaust gas components in the coolant.

Rent the test kit from a parts store, pay for the test fluid. Follow the instructions and don't try to make it better with long bubble times or workarounds. If you get ANY coolant in the test tube, wash it out with fresh water and start over.

https://www.google.com/search?q=ama...rome..69i57.9439j0j8&sourceid=chrome&ie=UTF-8

Some oil on one or more plugs in a Northstar is common - the plug well O-ring seals weep over time. Normal and not to worry.

 

[Ranger]

how do you do a block test?

https://youtu.be/DaDBhHyPogs