Car Running Weird - Need Suggestions

[jefffoxsr]

All of a sudden while drving the car started running weird. Not hesitating, not bogging, and not cutting out. It's just not running right.

The engine sounds different, and I think I hear valve train noise. I have broken many rocker arms in the past and I thought that's what it was since it was running and sounding similar to when I have broken rocker shafts.

Here's what I checked.

1. It's not a broken rocker shaft. They look good.
2. I did a compression test.
3. I tested the coil pack.
4. I changed the plugs.
5. The crank sensor looks good.
6. I swapped the MAF with a new GM delco one.
7. I tested the cam sensor with the Casper's cam tool.
8. No water in the oil.
9. Reset the computer a few times.
10. No error codes.
11. No vacuum leaks.
12. TPS voltage looks good on scan tool.
13. IAC reads good.

Here's an interesting clue. The new casper's knock detector was going off like crazy as I gently drove home 2 miles.

In park when I rev the car the Casper's knock detector will go off.

So it seems like there's valve train or some other noise. If I broke a valve or something then I would think it would show up in the compression test. I don't feel like doing a leakdown test since the cylinders were able to hold the compression reading for several minutes without falling at all.

What should I check now?

 

[QUIP'6']

wiped cam lobe maybe?

 

[jefffoxsr]

Thanks for the idea. I don't know anything about cam lobes.

I do know that the car has been running perfect and then all of a sudden it started running weird. I'm not sure if a wiped cam lobe would act like this.

 

[TurboBuRick]

Fuel pressure OK?

Try unpluging the maf and see if it runs better.

 

[jefffoxsr]

Before I swapped the MAF I unplugged it and nothing changed.

Thanks.

 

[TurboBuRick]

Does it seem like a dead miss or just running crappy? Fuel pressure is OK?

Whats the blm# warm @idle?

 

[jefffoxsr]

I'll check the fp tomorrow.
As far as your question about how it runs, that's hard to describe. It runs like one or two cylinders are not firing, or like spark is not timed right. It also runs like it has a vacuum leak.

No cutting out or bogging, or hesitating.

 

[Chuck Leeper]

Flat cam lobe and more going??

 

[QUIP'6']

wiped cam lobe maybe?

said it first so after you did your checklist you should be taking off your valvecovers

 

[jefffoxsr]

Thanks. Your response give me the impression that I can check if I have a wiped cam lobe by taking off the valve covers and then doing something.
Can you clear me up on this?

 

[Chuck Leeper]

Glad someone said it "first"!

 

[QUIP'6']

Thanks. Your response give me the impression that I can check if I have a wiped cam lobe by taking off the valve covers and then doing something.
Can you clear me up on this?

have some one bump motor over and watch rockers to see how high they are moving. especially #3 exhaust since these are common for wipeing out. are you running oil with zinc additive in it? if not you will definitly wipe a cam out

 

[bmackinnon]

Check all the maf, turbo, i/c, tb hoses?? hoping for a cheap fix.... :wink:

 

[jefffoxsr]

I really appreciate all the responses. I run Mobil 1 and I'm not sure if it has the zinc.

I checked the hoses and there's no vacuum leak.

It sounds like if a cam loped is wiped that you'd see a lack of movement on the rocker. If that's the case then I'll check it.

This problem was an "all of a sudden" situation where the car went from running perfect to running bad, so I'm not sure if a wiped lobe fits the bill.

 

[TurboBuRick]

That is correct. The rocker will not move like others. Also look for a cracked valve spring.

 

[jefffoxsr]

Thanks. I'll add those to the list of things to check this weekend.

 

[QUIP'6']

Thanks. I'll add those to the list of things to check this weekend.

also do you have the stock nylon timing chain? if so you may have jumped a tooth. i have seen them crack and loose teeth. also for a cheap fix you may want to check the grounds on the motor behind the head or get it running and pull each injector clip off and see if they make a difference in idle if you find any that dont make a difference them you may have found your problem. especially the one by the egr valve that gets burnt on it

 

[ct67_72]

does the car have a cat on it?

 

[jefffoxsr]

I like the idea of checking the injectors. The timing chain is not stock and as a reminder the car has only about 1,500 miles since the rebuild.

No cat on the car. No egr either.

The coil pack ohmed at 9500 to 9700 instead of 11000 to 13000, so I don't know if that's good or bad.

 

[bmackinnon]

The coil pack ohmed at 9500 to 9700 instead of 11000 to 13000, so I don't know if that's good or bad.

not good....