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bigbadchev84

bigbadchev84

1/2 ton status
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May 17, 2004
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Hermiston, Oregon
So I just picked up a 1990 fuel injected 350 fullsize blazer, its got a 350/205 that someone swapped in and has a strange noise. I am all to familiar with lifter and rod knock and it is definately not one of those, If you could imagine a rubber ball shaking in a pringles can. that is what it sounds like.

It does it more so right after being started for about 10-30 seconds goes away then only does it sparaticly, I have been trying to figure out where it comes from with a fuel hose to my ear, but cant track it down just yet.

It does it when driving, I never drove it over 25mph but it dosent seem to do it when revving to 3-4grand but will apear when it comes back to idle.

I pulled the inspection cover on the transmission and the flexplate isnt wobbling and I also unbolted the torque converter and slid it back away from the flexplate. started it and the same noise. Can a broken flexplate make noise with the convertor not hooked up?

I have also pulled the serpintine belt to eliminate any of the accesories it still did it. Any advice?
 
Im about 90% sure its not a pinging noise. The thing runs really good and revs awesome. It does however have a slight vibration to it at an idle, like its running rough
 
Ok got the transmission pulled today. Flexplate checks out. I pulled the oilpan and everything passed a visual. Pulled the plugs, looked to be running a little rich I will install new plugs tomorrow and dump some water down the intake while it is running to clean up the cylinder heads.

I did notice that there is no oxygen sensor on this thing. Could that have something to do with anything?

I have also pulled the valve covers and everything seems ok there too.

Maybe it is a rod knock? How can I diagnose which one it is?
 
Ok I have been doing alot of searching today. I will be installing new plugs tonight. The previous owner put a nice exaust system on this including headers, There is no oxygen sensor though.

They also swapped in some older gauges that dont work, so I have no check engine light.

What happens when there is no 02 sensor? I mean the thing seems to runn decent other than the rough idle and the knock. Could it be a lean knock? does that happen at idle?

I am a total noob when it comes to tbi.

Also where do i install a new 02 sensor? I will have to get a bung but where do i put it?
 
I don't think you'll be able to rule anything out until you get the oxygen sensor hooked up. It needs to be as close to the manifold as possible. You probably have no check engine light hooked up because the previous owner disconnected it because it was on all the time because of the missing oxy sensor.
 
So can i install it in any tube or down in the collector? The gauges appear to be late 70s gauges? I bought the truck with the knock, thinking it had to be a flexplate broken. Thats not the case.

The guy i bought it from got it from another guy that owed him money so he is of no help.

Also, could a stuck/bad egr valve do this?
 
OK i put new plugs in it today, the old ones were sooty. It fired right up and the noise is gone? what gives? It now does not run at an idle. revs up fine but will start to misfire.

where do i go from here?
 
You really need to get your o2 sensor hooked up, that is probably why your spark plugs are all sooty, you are running too rich w/out an o2 sensor. Also, go to your local parts store and see if they can connect a hand held scaner up to your truck, maybe you have a code that you don't know about since your engine light is out.
 
x2 on O2 sensor and the scanner.

Being a 90 is should be a simple one wire O2 sensor. Chase down the wire to verify though. It needs installed anywhere in front of the cat, the closer to the head the better. If you have no cat, it still needs installed. When the computer looks for signals, but doesn't get them it will do random weirdness in hopes of triggering the signal. One of the many problems it can cause is knocking. Newer cars also come with a knock sensor. haha haha.
 
Best off installing the O2 as far downstream as possible with headers, usually the collector. You could run it in a primary tube, but that means the ECM is not averaging the output of 4 cylinders, only one, and thats not a good thing.
 
dyeager535 said:
Best off installing the O2 as far downstream as possible with headers, usually the collector. You could run it in a primary tube, but that means the ECM is not averaging the output of 4 cylinders, only one, and thats not a good thing.
Click to expand...

Doh! I never think about headers...
 
dyeager535 is right. mount it as close to the head as possible but still in the collector so it registers for all the cylinders and not just one. you should be able to get a bung at your local parts store and get a good one like a bosch. i believe you want a downstream o2, not an upstream. i could be wrong about that though. can anyone clarify that?
 
there is only one oxy sensor on that thing so down/up stream doesnt matter, but if it did it would be an upstream sensor.
 
haha figures i would be wrong. i always get the two confused. thats one of the reasons i haven't decided to run fuel injection... that and im a broke high skool kid with an eddy 650 on a 305 and i think im doing alright... then i woke up!
 
Patriot makes header reducers with o2 bungs . One cut , one weld ( or band clamp ) and you can replace one of your reducers .
 
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