1999 v6 intermittent miss when warm

[theoldschooler]

My car decided recently that once it has been driven about 20 miles when it is hot out it will suddenly run like s***.
I replaced the plugs and changed the oil about 2k miles ago. I have no trouble codes, I hooked my laptop to pcm and checked the sensor readings everything seems okay.
I checked the manifold vacum at idle and it holds steady at around 20 inches.
I checked for oil in the coolant and vise versa, it looks okay.
I did the rag over the tailpipe trick and it only pulls back once and awhile
but I do not believe this to be a burnt valve because that should show up
on the vacum gauge right?
Possibly bad injector? Anyone know the ohm rating for my cars injectors? What about the coil packs, how do I test them?
I am considering doing a compression check this weekend but would like to test all electrical components first....
NOTE: When its cool out this car seemingly runs fine.

 

[wmburns]

IMO, you are jumping to big items much too quickly. Good diagnostic methods should test and rule things in/out and go where the test lead to.

I am going to assume that you have access to an ODB2 scanner and can monitor operational data. Have you looked at EGR flow? Excessive EGR flow will affect power especially at part throttle. There is a PID for EGR flow.

Also check the IAT values. Are they reasonable for the current weather? Check the engine coolant/cylinder head temperatures. What are they doing when the car begins to run poorly?

Is the total ignition system in good repair? Spark plugs? Spark plug wires? Coil pack?

A 1999 MY car is 11 years old. How old are the spark plug wires? At the least, try this old racer trick. Run the car in a totally dark location. Look for blue spark leaking out of the wires. Inspect the wires for white spots which is evidence of spark leaking from the wires.

Have you CLEANED the MAF? Use cleaner designed for the job.

Have you done a through job of looking for vacuum leaks? Remember that even a very small vacuum leak will cause problems.

Regarding injector measurements, this can only provide a crude functionality test. Consider instead an injector cleaning service such as injectorrx.com. Once cleaned/flow tested, the injectors are as good as new. Much cheaper than buying new injectors.

What about the condition of the cooling system? Does it hold pressure? Correct coolant level? Correct anti-freeze concertration? Does the cooling fan run? Is the radiator clean inside and out?

 

[theoldschooler]

Re:IMO

IMO, you are jumping to big items much too quickly. Good diagnostic methods should test and rule things in/out and go where the test lead to.

I am going to assume that you have access to an ODB2 scanner and can monitor operational data. Have you looked at EGR flow? Excessive EGR flow will affect power especially at part throttle. There is a PID for EGR flow.

Also check the IAT values. Are they reasonable for the current weather? Check the engine coolant/cylinder head temperatures. What are they doing when the car begins to run poorly?

Is the total ignition system in good repair? Spark plugs? Spark plug wires? Coil pack?

A 1999 MY car is 11 years old. How old are the spark plug wires? At the least, try this old racer trick. Run the car in a totally dark location. Look for blue spark leaking out of the wires. Inspect the wires for white spots which is evidence of spark leaking from the wires.

Have you CLEANED the MAF? Use cleaner designed for the job.

Have you done a through job of looking for vacuum leaks? Remember that even a very small vacuum leak will cause problems.

Regarding injector measurements, this can only provide a crude functionality test. Consider instead an injector cleaning service such as injectorrx.com. Once cleaned/flow tested, the injectors are as good as new. Much cheaper than buying new injectors.

What about the condition of the cooling system? Does it hold pressure? Correct coolant level? Correct anti-freeze concertration? Does the cooling fan run? Is the radiator clean inside and out?

I think you have a valid point..
Pulled plugs,I noticed #3 had corrosion on inside of the wire boot connection which was a
surprise because it was not there 2 months ago, I must of forgot the Anti-Corrosion Gel on
that cylinder.
Cleaned everything, runs better but still slight miss on one cylinder at low rpm under load.
Thinking I need new wires even though there is no arching and they appear to be in good condition, will need to find way to check coil packs..
Anyone know how many ohms these things are supposed to be?

 

[theoldschooler]

UPDATE

Okay that smooth running did not last long...
Now my car is barley running and SES light was flashing...
Luckily I was not far from home so with a light foot (to keep the SES light
off) I cruised home and parked it.
I know its the PCM sensing misfire from extra oxygen
the O2 is picking up so I`m leaning toward coil pack or injectors and maybe the MAF.
I will disconnect the MAF tomorrow and see If it fairs better in limp mode which
was a trick I learned while fixing a friends 5.0.
Also I noticed by a diagram online of the EDIS
system the crank sensor is directly connected to the ignition module,
Anyway of testing the crank sensor?

 

[wmburns]

Don't make this harder than it has to be. The blinking SES light means there is a MISFIRE occuring. Continue to concertrate on an Ignition problem until you are positive the ingition is perfect.

When the ignition is perfect, look for a fuel injector problem.

Go to your local auto parts and have the DTC codes download. They may have to access the "pending" trouble codes. Post.

CLEAN the MAF. It has to be working or your symptoms would be much different. Use only cleaner designed for the job.

Are you a glass half empty or a glass half full sort of guy?

 

[theoldschooler]

UPDATE 2

Well the PCM is in denial because there is still not one DTC.
I started the car this morning and it was running fine which
blew my freaking mind.
I am going to grab a Hayes manual to get the specs for testing all
sensors and coil packs because I cannot find it online.
I will post them later for all to benefit.
A thanks to wmburns for trying.
I will let you know what happens...

 

[theoldschooler]

VICTORY

I heard a familiar sound on the way to the parts store, I realized it was an ignition problem..
Replaced the ignition wire set and that resolved the issue.
The old ones were arching were they were routed on the back of the block and I did not see the marks on them till i removed the protective loom from them.
They were only $30 if you have a miss I`d replace these first and clean the plugs.

 

[wmburns]

A 1999 MY car is 11 years old. How old are the spark plug wires? At the least, try this old racer trick. Run the car in a totally dark location. Look for blue spark leaking out of the wires. Inspect the wires for white spots which is evidence of spark leaking from the wires.

First reply

Don't make this harder than it has to be. The blinking SES light means there is a MISFIRE occuring. Continue to concertrate on an Ignition problem until you are positive the ingition is perfect.

2nd reply.

A thanks to wmburns for trying.
I will let you know what happens...

Trying? Sounds like you didn't believe. How did testing of all the sensors go? Results of the compression test? Did you find a burnt valve?

I heard a familiar sound on the way to the parts store, I realized it was an ignition problem..

Just wondering, At the end of the day, did the forums help you? Was the advice given incorrect? I ask because from the last update it doesn't seam like you got any help at all.