puzzler after installing new head gaskets

[roscoe67]

Hi, I am posting this because I am completely stumped.

I had to replace a head gasket on the driver side, but went ahead and pulled them both and had them done over at a machine shop. I reinstalled them, following standard procedure, and buttoned it up, connecting everything (I was careful about marking every hose and wire, and nothing is hanging loose).

It seems to idle fine, but when driving, it essentially won't go above 2500 RPMs. It almost seems as if there is no advance.

I know the timing is correct - I have since pulled off the timing cover and the camshaft marks line up when at TDC. I seem to have spark all around - I have replaced the spark plug wires and even hooked up an analog induction timing gun and cylinder 1 and 2 are firing.

Strangely, OBDII says 'random misfires' and misfires in 2, 4, and 6, which really has me confused. I put a dowel on injector 2 and it sounds like a normal injector.

Is this consistent with any kind of sensor failure? It worked fine until the head gasket failure. But it did sit a while - I got injured right after pulling it apart and it sat 8 months. But I can't understand what would have changed over that period in terms of the electronics.

Could it be the gas? Could the machine shop have mixed up the cam gearing? As far as I can tell it only fits together one way. Otherwise I am stumped.

 

[Smog-guy707]

Sounds like a timing issue if you are misfiring in one bank. You said timing marks I am assuming the ones on the sprockets, what about the cam timing from cam to cam? Did the machine shop assemble the head for you or did you do it yourself?

It Sucks but it can really be anything if it was stripped down that far




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[T.Tech]

Do you have the wires going from the ignition coil to the right companion cylinder? 1-4/2-5/ 3-6

 

[BoomerBob]

Sounds like a timing issue if you are misfiring in one bank. You said timing marks I am assuming the ones on the sprockets, what about the cam timing from cam to cam? Did the machine shop assemble the head for you or did you do it yourself?

It Sucks but it can really be anything if it was stripped down that far

To remove or install the heads on the 3.4L the cams must be removed so the head bolts can be installed and torqued to spec. The the cams go back in. Hopefully the installer installed the service bolt to keep the split gear aligned before removing them. It can be confusing when installing the cams because there are two dots on one cam gear and one dot on the other but if memory serves; there are also two dots on the one dot cam gear. Obviously if both the two dot marks were aligned then it wouldn't run right.

 

[19963.4lsr5]

To remove or install the heads on the 3.4L the cams must be removed so the head bolts can be installed and torqued to spec. The the cams go back in. Hopefully the installer installed the service bolt to keep the split gear aligned before removing them. It can be confusing when installing the cams because there are two dots on one cam gear and one dot on the other but if memory serves; there are also two dots on the one dot cam gear. Obviously if both the two dot marks were aligned then it wouldn't run right.

Good point.


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[roscoe67]

To remove or install the heads on the 3.4L the cams must be removed so the head bolts can be installed and torqued to spec. The the cams go back in. Hopefully the installer installed the service bolt to keep the split gear aligned before removing them. It can be confusing when installing the cams because there are two dots on one cam gear and one dot on the other but if memory serves; there are also two dots on the one dot cam gear. Obviously if both the two dot marks were aligned then it wouldn't run right.

When I pulled the camshafts I installed a service bolt, and it came back with my service bolt still in there. I was careful about aligning the dots on the cam gears (I even put a dot of white paint on the dots to keep track more easily, since they face the firewall).

My concern was about the camshafts being in the correct heads - but they can't go in but one way, correct?

 

[roscoe67]

To remove or install the heads on the 3.4L the cams must be removed so the head bolts can be installed and torqued to spec. The the cams go back in. Hopefully the installer installed the service bolt to keep the split gear aligned before removing them. It can be confusing when installing the cams because there are two dots on one cam gear and one dot on the other but if memory serves; there are also two dots on the one dot cam gear. Obviously if both the two dot marks were aligned then it wouldn't run right.

Hmm - I only ever saw one dot on the cam gears. One camshaft had a dot on a tooth, the other on then bottom of the 'gap' between two teeth.

 

[19963.4lsr5]

My cams had both sets of dots (180 out) and depending which cylinder bank you were working on determined which you lined up to remove or install.


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[BoomerBob]

When I pulled the camshafts I installed a service bolt, and it came back with my service bolt still in there. I was careful about aligning the dots on the cam gears (I even put a dot of white paint on the dots to keep track more easily, since they face the firewall).

My concern was about the camshafts being in the correct heads - but they can't go in but one way, correct?

Even if they were interchangeable the machine shop still adjusts the valve lash (if needed).

Sounds like you should be okay. I'd look elsewhere for the issue you're having.

 

[roscoe67]

Sounds like a timing issue if you are misfiring in one bank. You said timing marks I am assuming the ones on the sprockets, what about the cam timing from cam to cam? Did the machine shop assemble the head for you or did you do it yourself?

It Sucks but it can really be anything if it was stripped down that far

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I had to remove the cams in order to reinstall the head (the head bolts are under the cams). But I did everything one-at-a-time in order not to mix anything up, and made sure the dots on the gears were aligned.

 

[roscoe67]

My cams had both sets of dots (180 out) and depending which cylinder bank you were working on determined which you lined up to remove or install.


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That is interesting. Do you remember which sides related to which dots?

 

[Joelzy]

Mine had 2 sets of dots as well and the machine shop aligned them to the double dots and not the single dots. I was under the impression that the shop knew which way and installed them that way and didnt notice until i tried to put the pulleys on and realized the cams were 180 degrees off. I doubt this was your issue as you would have noticed the pulley timing marks being 180 off, right?

as stated above, definitely double check plug wires are on correct cyls

 

[19963.4lsr5]

That is interesting. Do you remember which sides related to which dots?

I happen to be pulling my exhaust cam on passenger side.

Two dots are passenger side and one dot is drivers.



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[roscoe67]

I happen to be pulling my exhaust cam on passenger side.

Two dots are passenger side and one dot is drivers.



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If you haven't closed it back up, could you post an image of the two dots? I didn't see them on the gears, just the image like the one above with one dot on each cam gear.

 

[roscoe67]

Mine had 2 sets of dots as well and the machine shop aligned them to the double dots and not the single dots. I was under the impression that the shop knew which way and installed them that way and didnt notice until i tried to put the pulleys on and realized the cams were 180 degrees off. I doubt this was your issue as you would have noticed the pulley timing marks being 180 off, right?

as stated above, definitely double check plug wires are on correct cyls

Hmm - I don't think I would have noticed. If the passenger side, say, was on the single dots, I would still have just rotated the pulley around to TDC. The two pulleys are independent, so I could have misaligned the cams in one head without seeing it at the pulley.

 

[19963.4lsr5]

I’ll try and get a picture of the two dots tomorrow. They are opposite of the single dot. Somewhere I have an extra set of cams. It will be easier taking a picture of them than the cams in the head because the dots face the firewall.

Get a rag and spray it with brake cleaner and wipe off the outside face and see if you can find the second set of dots. My cams are from a 97 and a 96 and both sets of cams have both dots on them.


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[Joelzy]

Hmm - I don't think I would have noticed. If the passenger side, say, was on the single dots, I would still have just rotated the pulley around to TDC. The two pulleys are independent, so I could have misaligned the cams in one head without seeing it at the pulley.

You should have noticed if the timing marks on your cam pulleys were 180 degrees off tdc.
If the cam gear dots are lined up correctly, the pin on the end of the cam should be facing up which will align the cam pulleys to tdc


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[roscoe67]

I’ll try and get a picture of the two dots tomorrow. They are opposite of the single dot. Somewhere I have an extra set of cams. It will be easier taking a picture of them than the cams in the head because the dots face the firewall.

Get a rag and spray it with brake cleaner and wipe off the outside face and see if you can find the second set of dots. My cams are from a 97 and a 96 and both sets of cams have both dots on them.


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Thanks - I appreciate that.

 

[roscoe67]

You should have noticed if the timing marks on your cam pulleys were 180 degrees off tdc.
If the cam gear dots are lined up correctly, the pin on the end of the cam should be facing up which will align the cam pulleys to tdc


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Ah - I see what you are saying. I aligned the dots, ignoring where the pin hole was (figuring to make sure of TDC later when installing the belt), which was obviously wrong.

 

[19963.4lsr5]

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