New Timing Belt kit installed, now has rough idle.

[tom.whitez34]

Hi everybody, this is my first post. This site is great... Here's some background on my issue... I hope some of you can give me your thoughts on this. I have a 1991 Z34 3.4L, 110,000 kms, automatic. I have done the o-ring replacement and have new fuel injectors. Here is my new problem. Two weeks ago the timing belt let go. It was the bad pulley. The shop I took it to installed a new timing belt kit (pulley, tensioner and belt). He said he set the timing as per the manual. After all was put together, the engine now has a rough idle. Rpm goes from about 900 down to 600 then back up to 900rpm again then drops down and stalls out. Another thing is that it now feels like it has more power while gassing it while driving in 3rd gear after 2500rpms (feels stronger at top end). I was told that I don't have any bent valves (the timing belt was broken but was missing some teeth when I was shown to me after it was taken out). It is not confirmed but I was told by the shop guy that I could possibly have a "Bent Camshaft". He said while it is running, it looks like there's a little wobble. I will be seeing the mechanic tomorrow at the shop but wanted to ask for any input first. Thanks. Here are my questions...
1. Assuming that the timing was set properly, it the such a thing as a bent camshaft?
2. If the timing was not set properly, does any of the above mentioned symptoms sound like the timing is off?
3. If the tension was too tight when installing the new timing belt, could this have bent the camshaft?
4. If something is bent, how could the engine have more power at top end than before and lousy low end (at idle)?
I thank you in advance to everybody. Hope some of you can give me some of your expert trouble-shooting thoughts, sincerely, Tom.whitez34

[SappySE107]

Never seen a bent camshaft. It could be the timing, more so than bent valves. It wouldn't have good power with bent valves. Id guess it is a vacuum leak from your description, or the EGR is stuck open. Maybe the banks aren't exactly the same, but EGR and a small vacuum leak will mess with idle more than full throttle. If it runs good everywhere else, that is a good sign.

[tom.whitez34]

Thanks Ben for your prompt reply. On one of the other threats I was reading, it mentioned that some manuals have the wrong information about the timing and that you should not use the existing marks to set the cam timing. How would one go about setting the timing if you don't have a benchmark to start from?

[timg]

I'd agree that it sounds like a vacuum leak. Also, unplugging or damaging the MAF frequently causes the surging idle you're seeing. I've had it quite a few times on my own car. Before you do anything else, make sure the MAF is plugged in.

Tim

[walterdude]

To the best of my knowledge MAF wasn't used until 1994.. Before that it was MAP only... He's working on a 91... Check for vac leaks... You can spray carb cleaner around any vacuum lines and listen for a change in the way it runs. I'd say it's not the LIM gasket as that will likely cause a VERY high idle when cold. When warmed up the gasket seals better and the high idle goes away... I'd check the vac lines first,,, there are plenty to leak!! And they get brittle/crack with age....
Good luck,,,,
Tom....

[timg]

Whoops. I missed that. Nice catch!

Tim

[Schurkey]

you should not use the existing marks to set the cam timing. How would one go about setting the timing if you don't have a benchmark to start from?

The existing marks are nothing but paint stripes. The entire issue is resolved by using the PROPER TOOLS and the official GM procedure, which 1. positively locate the camshafts in the proper alignment; and 2. therefore make the paint stripes redundant.

Find out what tools and procedures were used by your service provider.

[walterdude]

I forgot about the timing question!!! Here's a link, http://60degreev6.com/forum/showthre...Y-Degree-Wheel to make a degree wheel... You use the degree wheel and a long dial indicator to find TDC on #1 cylinder... You could use a long screwdriver or rod down the sparkplug hole to find TDC.... I like the indicator way myself,,, it's nice to really KNOW!!
Again good luck!!
Tom...

Also,, welcome to the site!!!

[vcrvi]

Hey there, first time I posted here, just joined a couple of weeks back. My son's 96 developed the same sort of miss at ideal only a few weeks ago. I changed all the wires and checked the plugs all good. Searched High and low for a vacuum leak and none found. It only happens every now and then., and I swear it starts up fine then almost like something energizes and miss starts. I am thinking EGR valve , doing the timing belt in a couple of weeks after school lets out going to change it out then. I will let you know what I find out . Please let me know what you find out. Great site by the way. Curt

[RedZMonte]

from the sounds of it i would also agree with retiming the cams correctly.. IIRC there is a walkthrew here on the site somewhere. never heard of bent cam shaft.. maybe bent gear but not a shaft.. bent valve would run bad all the time. can be checked with a compre test tho.

S

[tom.whitez34]

Hi guys, here's an update to my original post on Timing Belt/Now Rough Idle (question 1)... but I have developed another problem (question 2), hopefully someone can give some feedback. Update: the mechanic went back in and found a slight wobble with the back cam gear (not a bent camshaft). There are no belt shavings or anything that looks out of place, so it was not changed. He double-checked timing (cams) and put everything back together. It does run good (have low end and high end power). Idles decently. But one issue now is that there is a high-pitched sort-of-ticking sound that sounds like an exhaust leak coming from that side of the engine. But car runs good though. Question 1: Has anyone experienced this ticking sound before?
New problem came up: Now when I turn the key to start the engine, it hesitates 2 - 3 times before the engine fires up. You can hear the engine barely turning (2 - 3 times) then it just fires up nicely. Changed the battery, changed the starter, checked the cables and the same thing happens. When I start it up and shut it off a few times in a row, the hesitation gets worse. I was told it sounds mechanical not electrical. Question 2: Has anyone experienced this before? Thanks in advance, Tom.

[Schurkey]

Hi guys, here's an update to my original post on Timing Belt/Now Rough Idle (question 1)... but I have developed another problem (question 2), hopefully someone can give some feedback. Update: the mechanic went back in and found a slight wobble with the back cam gear (not a bent camshaft). There are no belt shavings or anything that looks out of place, so it was not changed. He double-checked timing (cams) and put everything back together. It does run good (have low end and high end power). Idles decently. But one issue now is that there is a high-pitched sort-of-ticking sound that sounds like an exhaust leak coming from that side of the engine. But car runs good though. Question 1: Has anyone experienced this ticking sound before?

Did he FIX the sprocket wobble?

Did he use the GM-style camshaft holders to assure cam timing is correct?

Did you have the ticking before? GM has a bulletin on lifter tick; I have parts to perform the service.

http://60degreev6.com/forum/showthread.php/49738-LQ1-Service-Bulletin-57-61-09-Lifter-tick-%28cold%29

New problem came up: Now when I turn the key to start the engine, it hesitates 2 - 3 times before the engine fires up. You can hear the engine barely turning (2 - 3 times) then it just fires up nicely. Changed the battery, changed the starter, checked the cables and the same thing happens. When I start it up and shut it off a few times in a row, the hesitation gets worse. I was told it sounds mechanical not electrical. Question 2: Has anyone experienced this before? Thanks in advance, Tom.

What is battery open-circuit (No-Load) voltage? Better be about 12.6--12.7.

What is the initial timing?

How much voltage drop between battery and starter on the + side; and how much voltage drop between starter and battery on the - side?

[tom.whitez34]

Thanks for your reply, schurkey. I'll be seeing the mechanic on Monday and will ask the questions and have him check with voltmeter. May I ask you for your opinion, do you think the hard starting (no clicking sounds, just 2-3 hesitations then it fires up unless I start and shut off a few times, then on the 4th time I turn the key, I get nothing, no turning over what-so-ever and I can see the dash light dim when turning the key (the hesitations gets worse as the engine gets hotter). When I let car sit for 1 hour or so and cools down, it fires up with only a slight hesitation. Do you think this hard starting problem and the engine ticking sound (that sounds like a exhaust leak) is somehow connected from the timing not be set right?

[Schurkey]

Do you think this hard starting problem and the engine ticking sound (that sounds like a exhaust leak) is somehow connected from the timing not be set right?

Anything is possible. First guess: NO.

I think you've got a defect in the starting/charging system. Perhaps defective battery, perhaps defective starter, perhaps defective cables between starter and battery. Maybe more than one problem.

I also suspect that the ticking and the hard crankinging are totally un-related.

How do you know it ISN'T an exhaust leak?

[tom.whitez34]

Latest Update...FIXED Problem.
I want to thank all you who gave me some input to my problem and thank you for this great site. I read through most of the past posts on timing issues and there is so much very valuable info that people already experienced. It was a great help to me. All the symptoms I had were caused by the cams being set at both banks facing down. One bank was 180 degrees off. The mechanic went by one of the manuals he had and there was a misprint. So anyone that is going to do their timing, make sure you go by this site's info (some manuals say you end up with both banks facing the same way and then a later, corrected version comes out but it could be too late). Here are some of the symptoms that I encountered when the banks are set wrong.
-Engine cranks and starts but if you turn off and re-start again, (especially when engine is hotter), the more you do it, the more hesitation you get until the starter can not even turn the motor (sounds like a failing battery or starter but it's because of too much compression).
-When running, has choppy idle, stalls here and there but does run smoother in drive at about 2000 - 2500rpm.
-Engine sounds like a high-pitched exhaust leak or very noisy lifter tick (sound comes from under the plenum area).
-You know something is not right but it still starts and runs and has some power still.
So thanks again to Ben and everyone.
**So now I don't have to continue to drive my Z34, that sounds like a double 3 cylinder engine.