Oil Pressure Dropping and a Misfire on #1

[Inferno333]

Okay fellow TB owners. I've got another problem with my 2006 Trailblazer V8.

I changed the plugs and wires about six months ago when multiple misfires started. It ran awesome up until two days ago. My wife calls and says it's running rough again.

Bam. Cylinder 1 misfire.

The next night she says the oil pressure kept dropping to nothing and the HUD told her to stop the engine.

Turns out the oil was really low. We've been busy and I spaced checking it. All my fault. I filled it back up and starting trying to diagnose the misfire.

The coil pack is fine. The misfire didn't follow to cylinder 3 when I changed the connector. I pulled the plug on #1 and it was wet and fouled. It had a lot of carbon on it too.

The oil pressure is still dropping to nothing when driving.

It's going to my mechanic tonight, but I need ideas.

 

[Mooseman]

Could be a bad oil pressure sensor. No noises from the engine?

Do a compression test on the cylinder with the misfire to rule that out. After that, I would suspect a leaking fuel injector.

 

[BlazingTrails]

If you have a good coil on the fouled plug you probably have little to no compression in that cylinder. You could also have a blown head gasket and that could be water on that plug. There are more possibilities but those to me seem the most plausible.

 

[Mooseman]

I had a similar thing on my old 4.3L Jimmy. Turned out to be a cracked head.

 

[badazzbulldog]

I went thru this with my 02 silverado I put together this past spring sounds like you have a bad injector on no.1 cyl and its leaking bad enuff that its probably washing down the cyl and getting to the oil.pull the dipstick and see if there is a gas odor to the oil on the stick.

also on the oil pressure issue, on the 99 silverado I had 4.8 motor previous owner wasnt to consistent with oil changes I bought the truck knowing the trans was n/g and possibly the motor due to oil pressure dropping to zero after hitting operating temp.just for the hell of it before I bought a motor and trans I ran the truck with seafoam in the crankcase for about an hour idling in my driveway changed the oil lots of sludge came out. did fresh filter and oil another bottle of seafoam same thing 1hr idling changed again lot more crap came out fresh oil/filter again 60 psi on gauge at idle just below 80 driving never had an issue after that had truck for 4yrs till this past winter when it got totaled by a moron running a red light.

 

[Inferno333]

Could be a bad oil pressure sensor. No noises from the engine?

Do a compression test on the cylinder with the misfire to rule that out. After that, I would suspect a leaking fuel injector.

There's always been a tick coming from the engine. I've never been able to fully discern if it's valve train noise or a really tiny exhaust leak. I'm leaning toward the valve train since these burn so much oil.

I'll have my mechanic check that sensor and run a compression check on all the cylinders. I wouldn't mind knowing where they sit.

 

[Inferno333]

The Chiltons manual said all 2005+ V8s have the AFM. Is that true? I thought it was just the EXT models.

I'll mention the bad injector to him also. I forgot to smell the oil, but I've always thought the oil fill cap smelled a little like gas.

Glad this thing is paid off in February! Probably going to leave GM behind after the last couple I've owned.

 

[C-ya]

All the V8 LH6 motors have AFM/DOD. If you have an LH6 RPO code, you have AFM/DOD.

My oil pressure switch was dropping pressure as well. I know the oil pump doesn't work that way. If it is moving oil, it should always be moving oil. (I know gears can strip, but it wouldn't exhibit the same behavior.) The gauge responds to the sending unit. If the sending unit flakes, the switch flakes. The sending unit reports to the ECM, which gives you a nice raucous alert. I changed my sending unit and have not had any trouble since.

Oh, and spend $100 with Jeremy (LimeSwap) and get that AFM/DOD crap turned off! I did, and I love it. I'm using less oil now, too. Guess I should update my sig line.)

 

[Inferno333]

Well folks... I got the news about the misfire. It appears that a lifter on cylinder #1 is stuck.

I was quoted $2850 for all the lifters to be replaced and $1600 for just the stuck one.

I'm about ready to just drive the damn thing with a misfire.

 

[badazzbulldog]

watch this we did this on my neighbors 08 silverado cured misfire and tick it had when starting in morning

 

[Inferno333]

I'm debating that method. I'd want to just pull both covers and do all the lifters. My mechanic said that he tried a few different things to get it unstuck, but he thinks it's broken or seized up.

I'm also checking into the DOD delete kits.

 

[Mooseman]

The non DOD lifters might be cheaper which would reduce the costs. Either way, the PCM would still need to be tuned to turn it off.

 

[Inferno333]

Looks like I'll be getting rid of the DOD.

I'm in talks with BTR and PCM.

Any opinions or experiences people would like to share?

 

[Inferno333]

DOD delete kit is enroute to me from PCMofNC.

Turned out to be $785 shipped plus the $50+ shipping for the PCM reflash.

I'm looking forward to how it it'll run without it.

 

[Inferno333]

The truck is getting fixed as we speak. I'm looking forward to how it will run with the delete kit.

I'm having him put a new wheel bearing on plus change the water pump. I figured he might as well since he'll have it all pulled apart. I forgot to mention about any pulleys or bearings and the serpentine belt though.

 

[C-ya]

Good deal! Sorry to hear it's costing so much, but hey, them's the breaks.

 

[Inferno333]

Got it back tonight. Obviously running on 4 cylinders since the reflash hasn't been done.

Where the heck is the ECM??? I need to get it shipped out tonight.

 

[Mooseman]

It's right on the intake manifold. Can't miss it.

Edit: D'oh! It's a V8. Looking directly down from the front of the truck, it's down to the right of the fan (driver side). There is a plastic cover. Remove the cover, it is held by clips.

 

[Inferno333]

Thanks!

Is there a trick to getting the connectors to come off?

Thought it was just folding up the hinge lock. They don't want to budge.

 

[Inferno333]

Got it!

 

[Inferno333]

Update:

It's been almost two months since this thing got fixed. It was running pretty damn good until two days ago.

I was pulling a lightly loaded 6x12 uhaul trailer from Waterloo, IA back to Omaha, NE. Everything was all good until a little ways out from home. Light pops up and the pending code is a cylinder 8 misfire. I got it home, parked it, and let it sit overnight. I checked it again and the same code was on cylinder 7 only this time.

It's been running a bit rough since then. I put nearly 4 tanks of fuel through it in a 24 period. Could I have gotten some bad fuel and that's causing random misfires?

The wife is pissed since we just put an assload of money into this thing to get it running. I was hoping to keep it a while longer since it's paid off next month, but the other half has different ideas.

 

[Mooseman]

Could be a bad coil or two. Maybe swap 8 and 7 with 1 and 2. If the misfire(s) follow, then they are bad.

Don't wait too long. It could kill your cat(s).

 

[Inferno333]

I sure hope not. Getting tired of dumping money into this thing. Based on my last couple GM vehicles I won't be buying another.

I'll give it a try in a few days. The temp is -20 with the wind chill right now. Shouldn't be too hard to accomplish right?

 

[C-ya]

No, the coil should be a connector and a bolt or 2. Should be a fairly straightforward swap.

 

[Inferno333]

No, the coil should be a connector and a bolt or 2. Should be a fairly straightforward swap.

I see that now. Checked it before the wife went to work. I'll give that a go in the morning.

Are there specific brands that I should go with? And just pick the round or square based on whats in the truck now right?

 

[C-ya]

Not sure on the shape. I see that they offer two versions. I would go with what is on the truck, or the newer design. Rock Auto says the second design is round.

I wouldn't buy one until you determine that that is what is causing the issue. Although, there are some $10 on RA!

 

[Inferno333]

I didn't plan on buying it yet. I'll be checking them tomorrow afternoon.

Any experiences with the various brands?

I would almost bet the coil is bad. That's the plug that was barely hand tight when I changed them last spring. Plug eight was really loose too. Probably why I had a slight misfire on it too.

 

[Mooseman]

Go with OEM/ACDelco/Delphi. I had a Standard, was outlasted by the old ones still from original.

 

[Inferno333]

Go with OEM/ACDelco/Delphi. I had a Standard, was outlasted by the old ones still from original.

Thanks!

 

[Inferno333]

Definitely confused now.

I swapped the 5 & 7 ignition coils. The pending misfire code is still on #7.

Ideas?

 

[C-ya]

A fuel injector could cause a misfire if you have ruled out the plug, wire and coil.

 

[Inferno333]

A fuel injector could cause a misfire if you have ruled out the plug, wire and coil.

The plugs should all be good. They're under a year old. Same with the plug wires.

Can the coil be completely ruled out now since it didn't follow the switch?

Is there a way to test the injector? Is it hard to replace?

 

[Mooseman]

Before even looking at the injector, do a compression test on all the cylinders to ensure the misfire is not due to a mechanical failure like a valve or head gasket. I had a misfire like that on my old 4.3L Jimmy, wound up being a cracked head.

 

[C-ya]

Good call, Moose. I almost listed cylinder faults that cause compression loss, but didn't.

But yes, I would think the coil can be ruled out.

 

[Inferno333]

After all the work that was just done to this thing I'm betting the heads are good.

My mechanic builds racecars and showcars too. I trust that when he had the heads off putting in new lifters they were checked. Obviously new gaskets used throughout during that rebuild too.

I checked my Chiltons manual and it talks about pulling the fuel fuse and cranking the engine. Is that the best way to test the injector?

The truck ran and sounded perfect for nearly two months after all the lifters and a bunch of other stuff was replaced.

I just want an answer so I can rely on this thing.

 

[mrrsm]

Just out of curiosity.... Does your Valve Train seem a bit "noisy" at first when you start the engine... and then quiet down after the motor warms up when you are on an extended drive

 

[Inferno333]

Just out of curiosity.... Does your Valve Train seem a bit "noisy" at first when you start the engine... and then quiet down after the motor warms up when you are on an extended drive

I'm going to make a new thread with the current issue since the thread title relates to a past issue that's been resolved.