Misfires after valve cover gasket change

Ok, everything is apart again, though the valve covers are still on. Only took half an hour! I got a slight whiff of fuel as I removed the lower plenum, but that was it. I can't see any obvious wiring problems, though I don't believe it's a mechanical fueling issue. I'm guessing (maybe I'm wrong?) that the fuel passes through cylinders 1, 3, and 5 before heading over to 2, 4, 6 and then returning to the tank. If there were a fuel pressure problem, I think I'd see misfires in the other cylinders and fuel pressure would be so I'm going to rule out a pinched fuel line or broken regulator.

The injectors all seemed to be undisturbed from the work - no surprise since I only unclipped their connectors when I was in there before.

How can I test that the injectors are getting a pulse from the harness? It's difficult to get my multimeter leads in the harness, but I think I could make it work. I know the engine won't run, without the MAF and such, but it may run long enough for me to see the injector harness produce some voltage. What voltage am I looking for?

 

Is it possible to take one out, and see if it squirts when engine cranks?
(CAREFULLY)

 

I don't think so. The fuel rail is bolted in place, and it holds the injectors to the ports. If I unbolt the fuel rail, the injectors will come with it. I've read that you really need to replace the injector o-rings when removing them - not something I have on hand. I'm considering going to the store to buy a noid light at this point.

 

I thought I actually identified a wiring fault in the plug wires, so I buttoned everything up and tried again, but it's no different. I guess if you're not getting fuel, there's no point in leaving the plug wires connected at all.

I did some research on testing the pulse at the injector and many people say to use a "noid light." I had an old LED left over from my computer and tried using that, however I saw no light when I cranked it. Coolant also spewed briefly from one of the disconnected lines. I'm considering tearing it down and putting a noid light on some of the injectors, but I'm curious if there's an easier way?

Maybe I need to pick up some injector o-rings and actually attempt to remove the fuel rail. The two rails on each cylinder bank are connected via hard lines, so it seems like I'd have to lift up both rails at once - this does not look like a simple check to see if the injectors are spraying fuel...

 

Ok, I gave up and planned to move by bike back into the garage, so I pulled out of the driveway and went to turn around. I noticed that under an acceleration load, the truck actually seems smooth. It might even be at full power. When I let it idle, however, the idle returns to being poor and lopey like I have a big cam in it. I know a vacuum leak can cause poor idle. I didn't have an issue putting the upper and lower plenums back on, but I also didn't replace the manifold gaskets, though they looked fine.

 

Injector operation can be verified with a stethoscope. Just place in on there and listen. If you don't have one, a screwdriver with your ear on the handle will work in a pinch.

 

Since the truck was running "great" I decided to clear the codes and run an errand. It seemed fine on the road with good power, though the idle was always lopey. I got a new code right before I got home: P0171 which says Bank 1 is too lean. Despite this being a V6, I think since there's only one O2 sensor, it's just reading lean in general.

At this point I suspect it might be a vacuum leak, but I'm not holding my breath. I checked my clamps and hoses. They all look decent, though there are a few hairline cracks around some of the hoses when the clamps are removed. With the clamps on, there are no cracks.

I also checked the injectors with a screwdriver. I notice pronounced clicking in 5 out of 6. I have no idea how you'd check cylinder 6 since it's buried under the intake manifold. I was surprised I was able to get to #4.

 

check you throttle body gasket and make sure it is oriented correctly. mind idled shitty and threw a p0171 because of this. also check out the IAC valve and its gasket.

 

I actually didn't remove the TB. It stayed attached to the upper plenum. I also didn't move the IAC valve, so I'm not suspecting those.

I'm likely going to try hunting down a vacuum leak with some carb cleaner.

 

Didn't get my hands on any carb cleaner, but I did source a propane torch. I plan to try searching for the vacuum leak when I get home tomorrow.

I checked the short term fuel trim while picking up the torch and found that it's pegged at 19.5% at idle. I'm guessing this is the maximum amount of extra fuel that can be added based on the O2 sensor readings. Driving around town usually had it up about 5-15%.

Since I've had the truck apart twice, I'm pretty familiar with all of the vacuum hoses I disconnected, so hopefully I can find the faulty hose without too much trouble.

 

Seems that I have a vacuum leak. It took a while with the propane as putting the propane near any of the suspect hoses did anything. It was only when I started poking around the center of the engine did I start to hear it rev up. I thought it was the hose going to the IAC, but it doesn't appear to be. Instead, I think it may be the plenum gasket where it reaches the manifold. Of course this is the absolute worst case scenario as I now have to tear it down for a 3rd time, but oh well, it goes pretty quick now. Picking up new gaskets from Advance, but probably won't be able to put them on until Friday morning. If there are any other suspect places dead center in the motor, let me know. Here's a picture, looks to be around the rear bolt on the lower plenum:

 

For what it's worth, I picked up a can of carb cleaner to test. It's much, much easier to test with the carb cleaner as you can be more specific as to where it's going. Though I had a propane torch with a hose and a small nozzle, with the fan moving all the air around, I wasn't really sure where the leak was.

The leak appears to be all along the left side of the lower plenum. I wonder if there's something impeding the seal, if it's a fouled gasket, or if the plenum was torqued down incorrectly during reassembly.

 

Sounds like you got it under control. Replace it and see what's happens. And torque the bolts to spec. I wanna say it's actually a pretty low torque. Let us know what happens!

 

Everything is back to normal and idling perfectly again. It actually only took me 30 minutes to take everything down to the valve covers and put it all back together. I should open a business!

I replaced the gaskets with a new set from Advance, though I don't think the original gaskets were the problem. There is a support bracket on the driver's side of the engine for some hoses and cables to pass through. It was difficult to line up originally, but I made it work without much hassle. Unfortunately, I think "making it work" also made the plenum leak where it meets the manifold as it put too much torque on that side of the plenum. I elected to leave the bolt out of the bracket. It is difficult to move and I don't think this will be a problem longterm.



View from the front. There's a slight gap, and...



the holes don't line up. If I put this bolt in before I install the plenum/manifold bolts, the plenum will not sit correctly on the manifold, even when its bolts are torqued down. BTW, torque on these bolts/nuts is only 13 ft/lbs.

An electric ratchet with a 1/4" universal is worth its weight in gold when doing a job like this. Makes quick work of everything, and doesn't have the power to over-torque anything. Crack the nuts/bolts free, then spin off with the ratchet. Easy.

 

My question is why that bracket is off by that degree.
The flats and holes "should" line up on reassembly. It is a stiff bracket, I know. Which actually brings up another question as to if it is there just for hoses, why did they engineer it to be so stout?

 

You're right, that never sat right with me either. I thought I "won" when I got the bolt in originally. What I think happened was when I removed this bolt to remove bracket to get the valve cover off, I torqued the bottom bolt in place before getting the top bolt started so the bracket was not aligned properly.

I just went back outside to fix it.



When replacing this bracket, leave this bottom bolt loose during reassembly until you get...



this bolt installed and torqued down on the plenum.

As for the reason that bracket is so stout - maybe you can use the upper hook as a place to attach an engine hoist to R&R the engine?

 

Maybe. It is the only thing that makes sense.

 

did the re-adjusting re-tightening solve the missfire? I have had many issues with that dang bracket. mine has been giving me a P0302 for awhile now. i have tried everything just about. i might go home tonight and undo the bracket and see as mine has never lined up right.

 

That bracket is the engine lifting location, so it has to be stiff. Over the years the bracket gets hot and cold and hot and cold. Over time it will have a small amount of heat distortion. That is why it didn't line up well. As mentioned the best thing to do there is to loosen the lower bolts a little, then install and tighten the upper bolt.