1991 Fullsize Blazer Having problems.....

I'm in here asking anyone for some kind of input. I love my Blazer but at the end of my rope with it. I have tried just about everything to fix its problem and nothing has worked. I am hoping someone else had this problem and can give me some feedback.
Well to explain the problem!! It has been doing this for almost a year now. When you are at a speed of 45mph or lower trying to keep an idle speed it chugs and starts shaking. At that time my valves also rattle. If you give it gas, it will stop doing it.Its smells as though its running very rich from the smell of the exhaust.At first I thought bad gas..did a treatment and it solved nothing. Next I had the vacuum system checked out..nothing there. Next we did a tune up..new air filter and spark plugs and wires. That again didn't help. I was told the distributor cap by a mechanic..changed that..nothing. Next I was told the in line fuel filter..changed that..still not fixed. I then was told to try a higher level of octane fuel. Still no change. So you see I have spent alot of money and time on this. But yet the problem is not solved. The next thing on my list is the timing chain,gaskets and gears. If that does not work I will try the sending unit and fuel pump. Oh I have checked and replaced any fuel lines that I thought we're maybe causing it too. Its a new tank on it also. So if anyone has had this same problem or has a suggestion please feel free to comment. Thanks....Going Crazy Here............:banghead:

Welcome to Automotive Forums ChevyChic :cheers:

I would start by taking the distributer cap off, and seeing if there is any play in the distributer it's self. Just wiggle the router around.

I really doubt that it's the timing chain, since it would have skipped more than 1 tooth in a year if it was that loose. And probably wouldn't be running at all.

A much as I hate to say it, most of us have small Blazers, so if we can't help you you might want to check out the full sized truck section.
http://www.automotiveforums.com/vbulletin/forumdisplay.php?f=1090

Good luck with it

I would check the fuel pressure, not sure what the readings are suppose to be but I had a freind who had this problem and it finally died before we figured out it was the fuel pump. Just something to check.

Did you check that big EGR valve for being stuck/clogged etc cause on my TBI 89 Suburban I remember that would really screw up the idle if the passage clogged up. At idle you should be able to reach under the housing and push the diaphram up to open it and hear the idle drop (closed at idle). If its frozen and won't move replace - believe there may be another vac valve connected that opens it but I'm reaching back here. Also check throttle position sensor and may have an idle air solenoid on TBI - do a search on components to find tests (Autozone used to have these in how to fix section)

you mention idle speed at 45mph? Do you mean you get up to 45MPH and when your coasting its doing this, or do you mean when your cruising and it does this. Does it do it only under load, or just coasting? Mechanically, how is your engine? How does compression look in all the cylinders, how does vacuum look on the engine. You have to know or get an idea in the general condition of the engine before you try diagnosing what type of problem you have. Does the transmission shift properly, at all the shift points? Does it downshift at part and full throttle? Does it bog down and not downshift? Does it hesitate at all? Snap the throttle quickly, does it respnond right away, or do you hear a lifter clank or anything? Many questions must answered before you can solve your problem. When your idling like at a stop, how does it run? If it runs fine most of the time and mechanically checks out ok (compression test, vacuum readings) , chances are you have some electrical problem, most likely some type of computer problem.

Okay, let me explain this better. It starts with no problems. I have no check engine codes showing. I have had the vacuum system checked by a mechanic. The truck was running great. Matter of fact it went from Michigan to Georgia twice in a month. Also went to tennessee and North Carolina a month later. I had no problems with this truck until I fueled at a certain store. Thats why I thought bad gas at the time. Thats what it feels like to me. If anyone has ever had this situation of bad fuel then they know the feeling. But we did a treatment. Next we noticed that the fuel lines were not screwed all the way down allowing air to be sucked in and causing it to backfire in the motor. We tightened them down. Next we replace a fuel line that had rust holes leaking fuel. Still no change.Next we replaced the inline fuel filter, no change. Also did a tuneup and changed distribator cap. Still no change. Next I tried a higher octane fuel. Nothing is wrong with the distribator, checked that. Okay now to explain what it feels like and smells like. The exhaust smells very rich, like its getting too much fuel. The exhaust looks fine..no abnormal coloring to it. The Tranny was rebuilt a yr ago. It shifts fine.The engine sounds normal when idling. And no its not under a load. When you drive the truck, everything feels fine. Its when your driving at speeds lower than 50mph. Or when you go uphill. As soon as you apply more gas,the truck stops doing it. It does not do it when coasting. What I meant by idle speed ..was when your trying to maintain a certain speed under 50mph. It chugs and shakes to best describe the feeling of it. I don't know if this explains it any better. And yes, I'm leiry of Mechanics....I have sent my autos to them and got them back with the same problems. All it costs me is more and more money and they still don't fix it. So if its something I can do myself one thing at a time and save myself the extra money...I will do it. If its something I can't do myself then I will pay a mechanic to do the repair. Sorry not all mechanics are bad...I have just had very bad experinces with them.:frown:

Sounds like a timing problem.

Has the timing been set with the timing wire unattached from the PCM?