The Alchemist

iTrader: (19)

My wife has a 2005 Saab 9-7x which is just a rebadged Trailblazer/Envoy, and it's had a miss in #6 for a while now at idle. I've swapped plugs, coils, cleaned the intake track with Seafoam, and nothing has helped.

I was reading, and supposedly the 03-06 I-6 had soft valve seats and there's a few TSB's about them, and it requires a revised cylinder head.

I've looked into doing it myself, but there's no way I'm comfortable doing it.

So does anyone know much about them, or is comfortable working on them?

Thanks.

04qsgtoMA

iTrader: (5)

RUn a compression test and cylinder leakdown to confirm its a cylinder sealing problem first. I have also seen these with bad fuel injectors as well.

The Alchemist

iTrader: (19)

Yeah, in my stupidity yesterday, I was checking plugs, coils etc and misthreaded the plug into #6. It's probably fubar'd at this point.

So to fix that, the head has to come off. If the injector is clogged, or not running right at idle, I'd still have to pull the intake manifold. I looked at that yesterday and what a bear of a project that looks like. It makes swapping an LS intake look like a cake walk.

I argued with my wife at the time to get the 5.3 version, and she wouldn't listen. I finally gave in to get the 4.2 when we found out there were no 5.3's in stock, and they gave us a nice discount to buy a 4.2 from inventory.

Now it's probably going to cost me upwards of $3500 to get this fixed. Part of me wants to just trade it in, but the car is paid off, so if I get another year or two out of it, I'll save that $3500 plus in not having a car payment.

This sucks.

dschmittie1

iTrader: (64)

I work on them. Have done a few heads on 4.2 but not as many heads as I have done on 3.5s and 2.8s(5 and 4 cylinder version) They aren't alot of fun and require a special tool(that holds the timing chain) to pull just the head with out pulling the front diff, oil pan and front cover.

Threads in the head for the spark plug can likely be repaired if it is just a injector.

The Alchemist

iTrader: (19)

Dan, let me know if you would be interested in taking on this project. Without having a walk through or specs on the engine, I wasn't comfortable attempting to pull the intake manifold to get to the injector rail.

I'm sure the spark plug threads can be fixed, not sure if it can be done in the car though. I don't know, I'm really frustrated with this.

dschmittie1

iTrader: (64)

The intake isn't too bad to remove. It is harder than an F-body intake though. It is a pain to remove just to swap an injector to see if that is the problem. Although on the 4.2s I think I have seen more injector problems than heads.

I wouldn't be affraid to pull the intake and swap injectors around at home. But if the head needs pulled for the repair I am not sure that is something I want to tackel at home right now.

The Alchemist

iTrader: (19)

I'd be willing to drive to your place to swap the injector if you're up for it.

I understand that the head swap is complicated due to the overhead cams and what's required to hold the timing chain in place to do the swap.

If I can swap the injector, and see if the misfire moves, or hell, just put a new one in there, then it would be worth it to me. If the misfire remains at #6, then it's a case of figuring out where the misfire is coming from. Once you roll into the throttle, the misfire goes away, which I confirmed with HPtuners.

dschmittie1

iTrader: (64)

I would be willing to remove the intake and swap or replace the injector.

Both problems (injectors and head) show themselves very similar in the idle/very light throttle missfire

DannoWS6

iTrader: (5)

Just a couple other things to think about here.

Make sure you use the stock plugs for one, (Delco 41-103)

No oil in the plug well right? Doesn't happen often but the valve cover gasket could be leaking a bit.

Also #6 is prone to getting water on it. The hood seal around the cowl sometimes drips water on #6 as it gets older. You'll even notice this if you open your hood in the rain. Check to make sure that all the wiring to the coil looks good, nothing rusted or broken.

from Chilton Manual:

Check for battery voltage to the ignition coils from the ignition switch. Attach a 12 volt test light to the battery negative (-) terminal or other good ground. Disconnect the electrical connector from one of the ignition coils and check for power at the pink wire terminal. Battery voltage should be available with the ignition key on. if there is no battery voltage present, check the wiring and/or circuit between the under hood electrical center and ignition coil connector (don't forget to check the fuses). Also check the black wire terminal for continuity to the battery ground. If there is battery voltage at the coil, but there is no spark from the coil, the coil, crankshaft position sensor, PCM or wiring are likely culprits.

Check for a trigger signal from the PCM. Attach the lead of a test light to the positive battery terminal and touch the probe of the test light to the ignition control circuit terminal (it's the center terminal in the connector). Crank the engine. The test light should blink with the engine cranking if a trigger signal is present. Check each coil, if necessary. If a trigger signal is present at the coil, the power and ground circuits are good and there is no spark, replace the ignition coil. If a trigger signal is not present, check the crankshaft position sensor. If good, check the circuits from the coil to the PCM.



Chances are its probably the injector, but like you already mentioned 03-06 are known to sometimes be prone to valve issues. For your sake I hope its not the head that has to be pulled, a compression check will show it. Normal you should get close to 200, probably 180 with some miles, if its at 100'ish, not good.

How many miles on this truck? I have an 08 Envoy with about 76k on it and the only issue i have had was a cracked exhaust manifold (covered under warrenty) and a bad windshield washer pump. Otherwise its been running like a champ. I'm about to replace the original Michelins this month.

Let us know how it turns out.

The Alchemist

iTrader: (19)

Well, I'm headed to Dan's place on sunday to swap in a new injector to #6. I pulled the plug from #6 yesterday and it looked perfectly clean. Literally the ceramic by the electrode looked brand new. The plugs have abou 5-7k miles on them and they are the Delco 41-103 plugs.

I first noticed this issue when I swapped plugs at around 40k miles. I put in Denso's and shortly after that, noticed that it had a rough idle. Granted, I only ride in the car once every couple weeks, but noticed it when we came to a stop light that the car had a noticable miss. Hptuners confirmed that #6 was missing bad at idle. During the cycle, it would hit well above 100 misses while the other cylinders stayed at zero to 4 or 5 at most.

So I moved plugs, and coils, to no change. I then read about how the motor is picky with plugs, so I went back to the Delco 41-103's as well as did a seafoam treatment. The misfires were better, down to 20-40 each cycle, but it was better.

Recently it's gotten worse again. I scanned it today and it's back to the 100 misfires per cycle. I really hope it's just a crappy clogged injector, but if it's the head or valve issue, then it is what it is. Dan mentioned that it's roughly 15 hours labor to swap the head, plus the cost of a new head and miscelaneous items, so that's a good $1500-$2500, but with only 60k miles, it's worth it if it fixes the issues and I can let the wife drive it for another two or three years till the kids are out of daycare. 1, due to the expense of daycare, and 2, they will be older and hopefully won't trash a new car like they do this one.

traenknerperformance

iTrader: (1)

i own a shop in gibbstown, NJ just over the commadore barry- dont know how far i am from you but i worked at a GMC dealer for 7 years and have pulled 4 4.2 heads due to burnt valves. if you get in a bind let me know it wouldnt be a big deal at all for us to do- i have the timing chain retension tool here.

The Alchemist

iTrader: (19)

Good to know, and I'll keep that in mind if swapping the injector doesn't work. I'm hoping it does. I spoke with someone else today who mentioned that the bolts in the back on the manifold have come loose from time to time, creating a vacuum leak at idle. It's a plausible theory that we'll explore come Sunday.

traenknerperformance

iTrader: (1)

no problem man.... over the years on a missfire on a 4.2 we would check the coil out- if the coil was good it would end up being a valve issue. good luck man im hoping its an injector for your sake

dschmittie1

iTrader: (64)

I have worked in GM dealers for the last 9 years. I have seen a couple guys get burned that replaced heads on the 4.2s that ended up being injectors.

If it was a 3.5 or 2.8 I would say no question it needs a head

The Alchemist

iTrader: (19)

The way I look at it, a new injector was $50 to my door, and the labor to swap it is around 3.5 hours. If it's the injector, great, mission complete. If that doesn't fix it, then it's time to pull the head.

I'd rather go conservative at first rather than worst case scenario.

traenknerperformance

iTrader: (1)

first thing i always did was run the AFIT on missfires and i never once had a bad injector on a 4.2, we got paid like .4 for doing the AFIT so it wasnt a big deal to run it. usualy id run the afit, swap the coils, if i didnt find it id do a compression then a leak down. like i said i think i did 4 heads on 4.2s 99% of the time it was always a coil that caused a miss

The Alchemist

iTrader: (19)

First off, a big thanks to dschmittie1 for his help yesterday. Unfortunately, it wasn't a stinking injector, it's looking like a valve issue for sure. Using hp tuners we checked the manifold vacum and it's pretty steady, but listening to the exhaust, you can definitely hear a miss.

It sucks, but what can you do.

DannoWS6

iTrader: (5)

sucks bro

The Alchemist

iTrader: (19)

It does, but hopefully with Dan's help, we can get it fixed as quickly and painlessly as possible. It sucks because it's taking away from mod money, but oh well. My shortblock is just going to have to last and the rear and tires will wait to be replaced.

DannoWS6

iTrader: (5)

When you swap heads do you know if you can opt for the new style? I know in the later setup they changed the exhaust cam too and bumped output up to 291. Altough I'm sure you would need a tune to be optimal. So whats the plan anyways, are you just gonna rebuild the current one, thats probably the most cost affective approach?