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1991 Z34 3.4 DOHC issues


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Hey guys im still battling the issues in my beloved Z34. To give a quick recap my computer is giving me codes 12 (good diagnostics), 13 (O2 error) 32 (EGR error) and 44( Lean exhaust).

 

When i first posted i was having issues with rough idle and bad power loss and i fixed it by replacing a bad coil which i took off of a 3800 SC and it looked like the coil had been replaced before and the other two are stock. I had a homemade EGR block on the EGR when i bought it and me and my friend removed it and the EGR error went away for a while and now just has been popping up in the last week. I replaced the O2 sensor 3 weeks ago and the error went away. Well when i checked the computer about a week and a half ago i got the error again. And the strange thing is, the previous O2 sensor wasnt that dirty. I swapped them and got the same error and swapped back to the new one and got the error again. As for what has been replaced so far on the motor is as follows:

 

O2 sensor

Spark plugs ( AC Delco Iridium)

Spark Plug Wires (a basic set from a brand i never heard of dont remember)

MAP Sensor

Fuel Pressure Regulator

Valve Cover Gaskets

Upper Intake Gasket

Lower Intake Gasket will be done soon

Will be replacing my Primary Fan Motor soon too as that is now shot

 

For doing the lower intake gaskets what are things i should do while the motor is apart since i know its going to be a headache to tear down? I dont want to tear it apart again so soon after this. But yeah i got no idea at this point why the car is still lean, even after i replaced the O2 sensor the only code after it ran for 2 mins was 12 and 44 (lean exhaust). The car has a 2.5 inch exhaust installed with 2 glasspacks and tips no cat and ive had a 3.1mpfi Z24 that the exhaust fell of on and it didnt run lean at all. The coil i replaced when i looked at the other two coils they looked stock still. Ive tried searching my local scrapyards for anything with a LQ1 and there's none to be found. Is there another engine i could get a ICM from possibly? Its either 80 dollars or 325 dollars for a new one at my local O rileys. Any help would be appreciated because this engine has only 105k on it and i would like it to last as long as it can. And i thought the Chrysler 2.7 DOHC engine and tranni set up was a pain in the ass....

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I've done the lower intake gaskets on my LQ1 as well. It's not horrible, but you should get a fuel disconnect tool so you don't have the fuel rail dangling around while you work. IT can be done without taking them off but it's annoying.

 

Once you're in there, clean up the valleys as they've probably accumulated dirt and debris over the years. Change your spark plugs if you haven't done so already. You have to take off the rear spark plug cables to have clearance to remove the plenum. The plenum will pull up the rear spark plug cables regardless because the pull tabs rest on the plenum. You'll have to change the UIM gasket again as well since that's a paper gasket. Change the O rings on the fuel injectors. They'll be flat and will probably get air in the holes if you don't change em out after removing them. Some people recommend that you change the O ring in the back where the distributor would have gone on a 2.8 engine (this engine is based off that engine). I forget the term for it, but someone will chime in and correct me. If you're not leaking oil from that area, I wouldn't touch it but I've gotten somewhat lucky with this engine.

 

Other that that,remember to torque down the LIM bolts. They should take 15 or so foot pounds. I know the 3800 takes 11 foot pounds.

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Ok ill try to clean up the injectors in there while im at it. But that still leaves the issues with my car running lean and my O2 apparently going dead a week after install. Anyone got any idea whats possibly going on?

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I had that issue when the LIM was bad. I also had a bit of coolant going into the back middle cylinder (forget the number, I think 3). It wasn't noticeable to make it run rough, but the spark plug boot was always wet.

 

Basically, when there's too much air going into the engine, it will cause it to run lean. That's what running lean means, it has more air going into the engine than fuel, so you have to figure out where air is pulling in that's not supposed to be there. The 2 major entrances of air are the LIM area (where the gaskets meet the surface) and vacuum leaks. You know those plastic lines running around the engine? Those are vacuum lines and if one of them is cracked or broken, it will suck in more air causing it to run rough and lean. As far as the o2 sensor code goes, you will throw an o2 sensor code if you're running lean. When my LIM was bad I threw that code all the time and the engine would run rich because of it. When the o2 sensor triggers a code, it will cause the computer to compensate and add more fuel regardless of what the o2 sensor would normally be saying.

 

Have you noticed a drop in your MPG or the car smelling like unburnt fuel? If so, it's all attributed to your LIM gasket going bad. These engines act very weird when the gasket is going bad. Mine would cut off when starting it, surge, and idle high until the engine warmed up. Then it had a shake and dropping it to neutral would make it rev up by itself.

 

Do the LIM gasket. It's 23 years old anyway so it wouldn't hurt to change it. You should have a year warranty on that o2 sensor, go back to the store and swap it out. Put the new o2 on your car, put a new LIM gasket on, put new injector o rings, clean your IAT sensor (The one that goes on the intake accordion), clean your MAF, clean/replace your filter, and make sure there's no cracks in your vacuum lines. If they are, patch up using rubber hose. You'll be hard pressed to find the vacuum lines anywhere. Doing a rubber hose patch fixes it right up. There's a diagram on the header panel area of how the vacuum lines are ran.

 

Another thing noteworthy is that you should place a very thin layer of RTV onto the mating surface of the LIM gasket on the engine block. Many say not to do it but if you add a VERY THIN layer of it, meaning you put a little bit of it on your finger and spread it, there's no harm and it helps the gasket stay in place better. There's a torque sequence to these bolts as well. One last thing, on top of the LIM where it meets the plenum, there's a rubber O ring that goes where the coolant goes down from the plenum. Make sure to replace that. The how to on here doesn't mention it so be careful about it. It's going to be an orange o ring that looks extremely worn out and will be hard to pick out. Get some needle nose pliers and change it. I used a little bit of RTV to hold that o ring in place as well, hasn't given me issues. A little bit means don't go liberal with it, be conservative! Also, make sure not to strip any bolts on the LIM or UIM otherwise you're in a world of problems.

 

Also, if you can, source a legit EGR delete kit or find a new EGR. Sometimes they can leak air and it will trigger the code. The EGR needs a gasket so be aware of that.

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Ok good, glad to know that, and i have a oil leak too and its in the general area by the exhaust manifold. Whats the best way to seal that oil drive shaft? And yeah i get maybe 250 miles to a tank right now and it does smell like unburnt fuel on occasion. ill let you guys know what happens with this repair!

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This post is the best way. http://www.w-body.com/showthread.php/76155-oil-pump-drive-seal-leaking-lq1?p=1152740&viewfull=1#post1152740

 

Use those 2 o rings and you'll be good from what I can gather. Mine doesn't leak there, it leaks towards the front so idk much about the oil drive shaft. Mine will only leak if I don't use the car frequently. If I let it sit, it will leak a bit when I start it. Not sure where it's coming from, but that's another story.

 

As far as your bad MPG, it does sound in line with running rich instead of running lean. I'm getting 15-17mpg right now but my trans doesn't recognize 4th for some reason. When I had the bad LIMG, I was getting 15 BEST and city driving killed a gallon of gas in 15 minutes of idling and moving a block. Are you sure you're running lean and not rich? In theory, you would waste less fuel running lean since it's less gas and more air, but I assume the PCM is dumping fuel into the engine once it triggers the o2 sensor code.

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Its what the computer keeps telling me with code 44 is lean exhaust but yeah i know the PCM was set up to dump more fuel into the mix when the o2 error comes up. Today im doing the LIM just gotta run to the parts store and pick up some Injector o rings. Speaking of trannis i gotta flush mine soon

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Hey guys well gaskets are installed and i cleaned out the intakes a little bit as well. Ran into a problem though, the small coolant hose that hooks around the lim that has a washer o ring and a washer of some sorts.... well i lost one of the washers and cant find it in the gravel and i was wondering what that hose is called. It plugs in right below the two fuel line connectors. I need to know so i can get the right hardware from the parts store tomorrow

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Are you talking about the hose that delivers water from the block up to the plenum that's hidden behind the throttle body where the coolant temperature sensor is?

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  • 2 weeks later...

yeah it was the quick disconnect. I replaced it with a new one. Now im running into another issue. So its been a few weeks and now when i start it belches smoke for a bit. It dont smell like antifreeze and it smells more like carbon and oil. A friend ran a can of seafoam through my intake vaccum into the valves and the car blew a crapload of white smoke while the seafoam was put into the lines. It smoked for a bit and we drove it around till it went away and it seems to run better. When i started it up that night it belched the same kind of smoke, just not as much. Oil was cleaner too after the seafoam. I started it 10 hours later leaving work and it didnt smoke at all. So idk what was wrong there but i wonder if i had some stuck valves and maybe thats why i was losing oil. Im honestly not too sure. This has been one rolling train wreck so far. Just hoping im getting to the end

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Depends. If you're seeing a bit of blue smoke for maybe 10-15 seconds after the car has been shut off for awhile, it could just be a small bit of oil working down past the valve guides during shutoff. If the amount is small, as I described, and you're not still losing excessive oil, it may not be that big a deal. My '95 LQ1 does this, and has for years.

yeah it was the quick disconnect. I replaced it with a new one. Now im running into another issue. So its been a few weeks and now when i start it belches smoke for a bit. It dont smell like antifreeze and it smells more like carbon and oil. A friend ran a can of seafoam through my intake vaccum into the valves and the car blew a crapload of white smoke while the seafoam was put into the lines. It smoked for a bit and we drove it around till it went away and it seems to run better. When i started it up that night it belched the same kind of smoke, just not as much. Oil was cleaner too after the seafoam. I started it 10 hours later leaving work and it didnt smoke at all. So idk what was wrong there but i wonder if i had some stuck valves and maybe thats why i was losing oil. Im honestly not too sure. This has been one rolling train wreck so far. Just hoping im getting to the end
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  • 1 month later...

Hey been a while, the car smokes for a few seconds and that's it. Smells bad too, otherwise now i'm losing a quart to a quart and a half of oil every two weeks, sometimes even more if i do a lot of long range driving. Now i got a coolant leak somewhere else that i'm trying to track down. One thing with the oil though, me and my friend got under the car and looked and towards the front bumper down around the bottom we saw a lot of oil on a line running somewhere, we didn't have enough of a lift to try to track it but can anyone shed some light on this? We haven't seen a oil cooler at all on the car, unless there is one and its hidden away somewhere. Gets expensive to buy oil all the time and i still trying to get this lean issue settled. As far as i know the head gasket hasnt been done and im begging to wonder if at 110,000 miles and the age of a 1991 these days of the gasket is gone. If thats the case how hard is it to do the gasket on this car and will i have to retime anything because i got zero timing equipment. If i have a shop do it how much should i expect to pay to get the head gasket replaced? Thanks in advance

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