I was done trying to troubleshoot bad vibration when 3.4 reached @ 45 mph. I could not pull code as engine light not on so I took it in so shop could pull code with that $4000+ high end OBD tester (cost me $75 for diagnostic). I told him about unusual amount of carbon around #1 plug and that the plug and wire boot around plug. And that the plug itself was actually loose in the block when I changed plugs out it during my futile troubleshooting week.

They call me back telling me they did compression test (fine) and that my injector was bad (now up to $375). Then a day later after tearing intake off they called me back and said that the intake valve on #1 was not moving. Removed valve cover and determined the lobe /ramp on the cam was worn off and now it would cost @ $1300-$1400. They said they could not detect this earlier and sometimes when troubleshooting this happens.

Told them I could not afford that right now and he said that it would still cost me $250 for gaskets, etc. already purchased just to put back together!

My original question is should the compression test and or OBD tester or other test during my original '$75' diagnostic have revealed bad cam?

I'm going to pick it up today (Mon. 10/04) prolly. Should I have to pay the whole $250 since they mis-diagnosed the problem originally?

 

If the #1 intake valve wasn't moving at all, compression on that cylinder would have been very, very low. If the valve doesn't open, then air can't get in to be compressed! They could have muffed the compression test by not blocking the throttle wide open during the test. I wouldnt be surprised if they didn't even do the compression test since it's a pain to get at the plugs.
I'm surprised that an oxygen sensor code wasn't set. With one dead cylinder due to no compression, the fuel injected into that cylinder wouldn't burn and therefore be pushed out during the exhaust stroke. The exhaust on that bank would have been rich, rich, rich. I wonder if they looked at the datastream while th engine was running or simply checked the computer for codes.
The diagnostic fee is typical and normal -- scan tools are expensive to buy and update.
Bummer for you. Are you going to drive the car with a dead cylinder? If you do you'll burn up the cat.
Replacing the cam is a nasty job. The whole front of the engine has to come off as well as the lower intake.

 

1400$ id just get a new motor ive seen in here b4 brand new 3.4s for 1100$

 

Finding a failed cam with a compression test would be difficult. If there is any of the lobe left on the cam at all it would not show up. Even if the valve only moved .05” the compression test is done at such a slow speed the cylinder would still have a chance to fill up.

Where you mechanic made his mistake was not doing a Vacuum test. A Vacuum test will show a valve train failure. When you have a engine miss and you suspect it is mechanical normally you test the vacuum with the engine running before you do a compression test.

In defense of your mechanic is pretty odd for a car to show up with no lobe on a cam. These normally wear out in stages. First the ticking, noise then a slight miss and higher RPMs with a tick, then a miss all the time with a tick, then no tic. I have seen bad cams miss diagnosed as bent push rods because owners did not tell the mechanic that the issue took weeks to develop.

 

Thanks all for your quick replies and advice. I wasn't sure about the compression indicating valve/cam failure. They did say that the intake valve was not even moving which means the lobe was prolly completely rounded. I'm going to pick up the car now.

I did have some ticking but at the same time over the past few weeks the engine was getting hotter than normal (sludgy radiator / non-related) and I added some engine treatment which seemed to make it go away a few days later.

Should I have to pay the whole $250 since they mis-diagnosed the problem originally?

 

I think if you want your car your going to have to pay them. You signed an agreement to pay in full before you get your car.

I would let them know you are not happy, that a simple 5 minute vaccum test should have shown the issue. They could not have quoted you a price based on the Vacuum test but they could have told you you had an internal engine problem very early in the process. Maybe they will cut you a break on the price. If not never go back.

 

I had a flat cam on a SB350. It showed up as low cylinder compression, Oil didnt help. Vacuum test showed eratic vacuum and a little lower than it should have been. I pulled the valve cover and used a mic on the pushrod end of the rocker and compaired it to the rest of the rockers on that side of the engine. It was a no brainer what happened. This lobe lifted 1/4" less than the others did, flat cam on intake lobe and exhaust lobe. The exhaust side was almost round intake had a little lift. I drove the truck like this for quite a while but finally the pressure got to the engine and I broke the rings on that cylinder. I pulled the rockers and pushrods out of that hole and still drove the truck and the engine didnt run any different than before. My 7cylinder 350 lasted me and the next owner about 3 years before he decided to give it a new engine. I dont think your 3.4L would run on 5 very well.

Your mechanic could have determined the condition of the cam well before taking the intake off the engine. You can feel if a pushrod is in the lifter or not and you can remove the pushrods without removing the intake to check if they are bent or not. Also alot of bigger shops and dealerships have the nice little camera that they can use inside the engine to see things before removing too many parts. I love using those cameras.

Massey

 

The thing was that I agreed verbally only to replace a fuel injector, that's all. When they started tearing things down is when they discovered the intake valve was not moving. I told them about the simple vacuum test indicating valve train issue somewhere and his response was that he did not know exactly what his mechanic did and that if we lived, "in a perfect world", than they would have caught it sooner. What kind of generic *** rhetoric is that! Won't ever go back that's for sure.

 

If you did not give verbal or written authorization to perform more than the injector then you are not liable to pay the labor of the additional work. If replacing the injector calls for the intake to be removed that is a different story, but I know it does not on your engine. I think the upper intake needs to be removed but I KNOW the lower can stay installed. On a 3.8L you can change injectors without taking the upper or lower intake off.

Check with your local and state laws about auto mechanic work that is not authorized, I can imagine you are not going to have to pay and his mechanic is going to have to absorb it on his time card.

Massey

 

Yeah the upper intake would have to come off for a bad injector but mine were fine. They were not authorized to take valve covers off and he kind of admitted that but made it sound like he was doing me a favor by not charging me for that part of the job. I don't think they expected me to say no to the newest estimate. I will prolly end up taking them to small claims court. I agreed to a $75 diagnostic and then I agreed to replacing one fuel injector which did not need replacing.