Slight Misfire/Shake at Idle After Head Gasket Job

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I was able to call a local dealership who found and ordered a replacement connector and pigtail.

For now I epoxied the pin into the connector and plugged it in. However I haven't noticed any change in the issue since doing this.

I am planning on checking the timing today and making sure it's set properly. If that checks out then I'll order a new ignition coil and see what happens. Let me know if you guys thing of any other possible causes
 
I'm still having this issue. I took it back to the shop and they found that one of the injectors was not working at idle. The injectors we're sent out to be cleaned and matched at the time of the head gasket. They checked and found the issue to be a bad connection which they fixed. I was in a big hurry to get the truck back from them since I was leaving for California that weekend and didn't want to leave it there for 2 weeks. So I drove it home and didn't really get a chance to check it.

I've been driving it all this week and the problem is still there. It shakes/vibrates at idle and the RPMs drop as low as 580. I replaced the coil last night with a brand new one and still no luck.

Anyone have any other ideas?
 
It would not be the first time I have seen injectors cleaned and serviced installed back into the truck and found injectors no longer work correctly.
 
ajax1 said:
It would not be the first time I have seen injectors cleaned and serviced installed back into the truck and found injectors no longer work correctly.
Click to expand...

Fair enough, this has also been on the back of my mind. Honestly there wasn't anything wrong with the injectors before the head gasket job but I did it more as a "while you're in there" thing.

I'm going to look at all the vacuum hoses and make sure they're routed correctly again, and then I'm going to inspect all the ignition system even though it's brand new. I doubt there's anything wrong with either since it's all brand new but I'll do it just for the sake of double checking.
 
Can you identify which cylinder is misfiring? Use a mechanic's stethoscope to hear the dead cylinder, then try moving the injector to a different cylinder.

If the miss follows you have a bad injector, if it stays you have a different problem.
 
Seth_O said:
Can you identify which cylinder is misfiring? Use a mechanic's stethoscope to hear the dead cylinder, then try moving the injector to a different cylinder.

If the miss follows you have a bad injector, if it stays you have a different problem.
Click to expand...

I don't necessarily think a cylinder is misfiring that's just how the car feels. It feels like a very minute missfire at idle.

However could what you suggested help me figure out if an injector is my problem? I do have a stethoscope and can hear all the injectors operating, but maybe one isn't operating as well as the others...
 
So I am back to trying to deal with this problem. After my last post I took it back to the original shop and they looked it over again for a couple of weeks. All they could find was that the spark plug gap was out of spec. Unfortunately this didn't fix the idle issue.

I've decided to tackle this issue by starting from scratch and thinking logically through it. I've made a list of the steps in which I'm going to tackle the issue. I'm sharing it here in hopes that you all can add other things that I should also check or simply change the order to be the most efficient, the list is as follows...

1. Check for obvious vacuum leaks (small vacuum hoses, air intake hose, throttle body gasket, manifold gaskets, etc.)
2. Check timing
3. Test oxygen sensors
4. Test TPS
5. Test IACV
6. Remove/clean throttle body
7. Adjust TPS if needed
8. Clean IACV
9. Reinstall throttle body and check for improvements
10. If no change, remove top part of intake manifold
11. Check wiring harness by EGR and re-wrap
12. Swap out injectors with a know good working set
13. Test engine coolant temp. sensor for ECU
14. Test VSV
15. Test Vacuum check valve by VSV
16. Verify vacuum hose routing and check for visible damage
17. Put everything back together and check for improvements
18. If no change, replace motor mounts
19. If no change, roll it off a cliff.
 
I'm working through that exact situation. Slight miss at idle, slightly rough at idle, little off on the rpm.
Except its cylinder 6 missing according to the scanner. The last drive it also said oxygen sensor bank one error. But that sensor is brand new and so is the harness.
Scanner thing says the ecu is adding fuel. Something like 35% at idle. Much less added fuel under throttle. I'm gonna look at the temp sensor next.
So, I'm no help, but in the same boat.
 
Tedward said:
I'm working through that exact situation. Slight miss at idle, slightly rough at idle, little off on the rpm.
Except its cylinder 6 missing according to the scanner. The last drive it also said oxygen sensor bank one error. But that sensor is brand new and so is the harness.
Scanner thing says the ecu is adding fuel. Something like 35% at idle. Much less added fuel under throttle. I'm gonna look at the temp sensor next.
So, I'm no help, but in the same boat.
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Definitely worth a shot. I just checked my temp sensor, even though it was replaced at the time of the rebuild, and it checked out fine on the chart. You should be able to check it while its still on. At this point I wish I had anything to go on, I'm just guessing/checking everything I can think of at this point.
 
My experience with a similar issue after my head gasket job at a first shop. The 1,3,5 cylinder bank was misfiring intermittently. Confirmed with a good old fashioned Heathkit oscilloscope my FIL had. First shop was useless. SD Trux ultimately found a couple of pinched wires, one of which led to the odd bank injectors from the ECU that we could see misfiring on the oscilloscope. That pinched wire was causing an intermittent ground fault and thus the misfire.

In all of what you've looked at, have you done a little shake of the wiring harness near the firewall to see if that induces the misfire? Inspect the wiring from the injectors back toward the ECU to see if they are all ok.

Good luck!
 
Brentbba said:
My experience with a similar issue after my head gasket job at a first shop. The 1,3,5 cylinder bank was misfiring intermittently. Confirmed with a good old fashioned Heathkit oscilloscope my FIL had. First shop was useless. SD Trux ultimately found a couple of pinched wires, one of which led to the odd bank injectors from the ECU that we could see misfiring on the oscilloscope. That pinched wire was causing an intermittent ground fault and thus the misfire.

In all of what you've looked at, have you done a little shake of the wiring harness near the firewall to see if that induces the misfire? Inspect the wiring from the injectors back toward the ECU to see if they are all ok.

Good luck!
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Thanks for the info. That is definitely on my list of stuff to recheck. Before the headgasket went I actually inspected the wiring harness while doing the valve cover gasket and they seemed to be in good shape. I simply taped them up and reinstalled everything.

After the head gasket job I began having the idle issue. It could very well be that whenever the shop was removing/installing everything a wire could've been damaged and causing the issue. I have checked the fuel injector connectors (the housings were also replaced during the head gasket job) and they appear to be in good working order. This weekend I plan on taking off the top of the manifold and I will unwrap the harness to check it again.
 
EPIC Cruisers said:
So I am back to trying to deal with this problem.
SNIP

I've decided to tackle this issue by starting from scratch and thinking logically through it. I've made a list of the steps in which I'm going to tackle the issue. I'm sharing it here in hopes that you all can add other things that I should also check or simply change the order to be the most efficient, the list is as follows...

1. Check for obvious vacuum leaks (small vacuum hoses, air intake hose, throttle body gasket, manifold gaskets, etc.)
SNIP
19. If no change, roll it off a cliff.
Click to expand...

As it is, 19) would be emotionally satisfying. I'd suggest substituting "If no change, part it out."

Dismemberment is pretty harsh punishment and your wallet will appreciate it, too.
 
greentruck said:
As it is, 19) would be emotionally satisfying. I'd suggest substituting "If no change, part it out."

Dismemberment is pretty harsh punishment and your wallet will appreciate it, too.
Click to expand...

Hahaha you are correct. Hopefully it doesn't come to that. My old BMW is very sensitive when it comes to vacuum leaks and I managed to get that idling perfectly. In my mind the 80 should be easier to fix but I'm beginning to doubt it...
 
@EP977, did you ever track down the source of your misfire? I'm currently having a similar situation and plan to start tracking it down next wee.
 
It ended up being....when the head was resurfaced and the valves adjusted, they were not done properly. Therefore a couple of valve clearances were out of spec. I took it back to the shop that did the head gasket, and the machine shop decided to grind the valve shims down to get them to spec. This wasn't my first choice, but the shop insisted that certain valve shim sizes were NLA so this would be the easier best/route. After talking with a few people it seems that the valve shims are actually still readily available, therefore in the near future I will have the shims replaced the correct way. Even after this I still have a very very slight stumble at idle, but it's way better than it was before. Hope this helps!
 
My slight misfire at idle plus the ecu adding fuel was due to the knucklehead that bolted the motor together, Me! I failed to torque the lower intake manifold to the head. I could hear what sounded like a vacum leak, sprayed card cleaner, triple checked lines, replaced stuff that didnt need be. Not until I was about to remove the head did I find my own error. It was sucking wind. Torqued the 13 fasteners and runs like a top again.
 
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