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couple chevy vortec questions


Dirtautoguy

Question

I have a 1996 chevy k1500 with a vortev 350. the truck has 230,000 miles here are some recent maintanance items I have done with it.

 

plugs

distributor

cap

rotor

wires

fuel pump

fuel injector cleaner

clean air filter

 

recently my mpg has dropped quite a bit from getting 17-20mpg I have only been getting 10-13 mpg. I have been watching my peramiters and this is what i have came up with.

 

font O2 sensors: they swing high and low like they are supposed to however they do tend to stay in the 75 80s range alot.

 

rear O2 sensors: seem to be all over the place especially on bank 1. it will stay in the 50-70 range for a short time then swing down to 10-20ish range.

 

fuel trims: are always negative especially at idle. as rpms go up it becomes less rich and closer to normal.

 

long term bank 1: -10 at idle and works down to -5 with rpm or speed

long term bank 2:-8 at idle and works down to about 0 or -3 with rpm or speed

 

knock retard: at idle hangs out around 20 and often reaches 40 or 45.

 

My first thought was a catalytic converter. I unbolted the exhaust where the front and rear halves come together and looked at the catalytic converter the one that I could see looked great and brand new. I couldnt see the other catalytic converter but I can beat on it and something inside it sounds loose. not heavy but loose.

 

A friend mentioned that I might have a leaking injector which I hear about the spider injectors with poppet valves. so I took a look inside the throttle body with a flashlight and i found that the lines I could see were wet. and there was also some puddles on the bottom of the intake. I did get a small smell of gas but its not clean where the puddle is and im not sure what the liquid is but I am sure it shouldnt be there. what are your guyses thoughts???

 

 

My other question is not related to this issue but I am curious.

 

is the updated 4l65e transmission a straight bolt up to my 96 k1500 with a 4l60e? from what i hae researched and understand they are about the same just with better internals. if/when the time comes to replace mine I wouldnt mind putting a heavier one in more just for piece of mind.

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upon further testing I think that you might be right. I had my wife raise the rpm to 2,000. I unplugged a vaccuum line to make it lean. and bank 1 upstream O2 sensor really took its time to change. bank 2 o2 sensor was a little faster but it did eventually change. and started giving gas rather than taking gas with a vaccuum leak. then i made it rich and it didnt seem to affect it much. and the same thing bank 2 was faster but didnt change instantly. and bank 1 didnt change real quick at all.

 

I dont know when or if they have been changed before. I know that I never have and i have put 40,000 on the truck and before I owned it it was a company work truck and they did minimal maintanance. oil changes and things they had to do.

 

So I think Ill start with a cheaper fix with the O2 sensors because they are obviously having issues.

 

since I dont have a fuel pressure tester I think I might go have one done at a local shop. what would that usually run??

 

My converters could be an issue but we dont have emissions testing here so if that is a issue ill deal with it then. otherwise ill just leave it untill it is causing issues.

 

 

I do eventually plan on replacing the motor as well. hopefully while i'm im school and can use it as a project sometime in the next year or two. I dont really tow with it other than a 4 wheeler/snowmobile trailer maybe 3 times a year at the most and no further than 30 miles so thats not a big deal.

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I decided to clean my air flow sensor because i recently cleaned and re oiled my air filter. it didnt seem to make much difference but while i had it all apart again I decided to check out under the throttle body again. this time it smelt pretty strong of gas and I looked with my flashlight again. only this time i looked more at an angle towards the firewall. it looked alot wetter to the point that i could see silver parts of the intake.

So just for the heck of it i decided to hook up my pressure tester gauge again and see what happened. It pressured up like normal and while i was waiting to see if it lost pressure something started randomly clicking. it would do it in bursts and then stop for a time and then do it again. as I watched the gauge with it clicking when it clicked the pressure would go down. the only thing that i can think of is that my injectors are opening when they are not supposed to.

From what I understand the poppet valves on this system open and open and close with pressure. GM put out a updated version that makes it more of a mpfi with electronic injectors instead. the injectors are under the top part of the intake manifold. this upgrade is supposed to be much better than the poppet valves and if thats what i need to do I would rather just replace them mostly because it seems like a lot of work to go in and just replace one smaller item and have the chance of haveing to do it again.

My fuel trims are about the same. at idle the short term trims climb as high as -11 as well as the long term fuel trims. if I am going 30 or 40 mph down the road the short term are around -5. and at 65mph the short term trims are 0-4 almost always negative hardly ever positive. It seems the slower I am going the more gas it has to take away. the faster Im going the better it gets.

I am using a scangauge 2 so I always have access to the trims and other info. the trims also seem worse if its a little colder outside.

I looked at the EGR valve and I think the liquid may have just from when i changed the thermostat.

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The computer is probably able to dial back fuel delivery enough, I suspect. Or, there could be a small vacuum leak at idle.

 

I know the intake gaskets are notorious on those years. My '00 4.3 had that exact problem. I didn't find it until I yanked the intake for a carburetor install in another vehicle. At that point I had given up and parted out the Jimmy it came out of. Biggest money pit I've ever seen in my life! Only 106k on it when we bought it. Parted it by 145k ...

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I was getting a P0303 code on my son's 4.3L S10. I just put a new fuel pump in about 6 months ago. I did a little research and decided to put in a new fuel injector spider. I got the Standard Motor Products unit. It is the updated style of the mpfi. I can tell you there is a night and day difference on how the truck runs. It is smoother, accelerates better, and when you put your foot in it is much more responsive . I highly recommend changing yours out for one of the new mpfi units. If you have a fuel filter outside of the tank, did you change that?

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Don't worry about the rear sensors - those sole purpose is telling the computer the condition of the catalytic converters (and cleaning out your wallet if your area tests for emissions - they're real good at doing that .... ). It does absolutely nothing for the running condition of your truck. Useless items. A clogged cat will , however, kill your performance and fuel mileage BIG time ... so if the trims are fluctuating there, that cat could be clogged up.

 

Your fuel trims suggest it's more than likely one or both O2 sensors failiing (getting lazy) - you should see rapid and constant switching, never lingering in one area of voltage at all. It very well could be that damn spider as well - that is a craptastic design. Not one of GM's better brainstorms, that's for sure ...

 

I can't help you with the knock retard parameters - never tested those, so I don't know where they're supposed to be.

 

Don't waste the effort in trying to upgrade the tranny, especially with the stock engine. With that kind of miles, you could use all the money and effort into fixing all the other little things that will inevitably be failing soon. Another 4L60E, or a rebuild will outlast the truck more than likely. If you tow alot, add the biggest cooler you can find, and you'll be fine. The addition of a Corvette servo will help the clutches last quite a bit longer as well. Anything to firm up the shifts - quick shifts are better than slushy, slow shifts for longevity. Slushboxes .... that's what I call stock transmissions. Just my .02 ...

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I have replaced the front O2 sensors and my ignition coil. My mpg and throttle response is a little bit better. but Im still missing 2 or 3 mpg and it is still running rich at idle. my idle itself has went down closer to 600.

 

my long term have been at -9 and -8 and at idle it seems like the shake has gotten worse. I got a fuel pressure tester and the pressure was in spec and the pressure didnt bleed down.

 

I did notice that around the egr valve by the thermostat there is a liquid leaking from the egr valve. I'm not sure if its gas or oil or what it is. although im pretty sure that would cause a vaccuum leak. but then wouldnt a vaccuum leak make it lean?

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