I have a 94 Blazer that I've had for a few months now. Bought it used and it has over 100k but how much over I don't know as the odometer broke at 100K. Ran great when we bought it but after a few ekks it started acting up. I found the the vacuum hose on the back of the intake manifold had come off because it was cracked and worn. I replaced that, checked for other leaks, found none, and it ran fine.

A few weeks later it really started acting up. It wouldn't start right away, the idle started getting rough, and then one day on a drive back home from town it took forever to start and sounded like it was only firing on a few cylinders. The whole thing shook, and was not responsive and bogged on acceleration until it got the rpms up and then it smoothed out somewhat, well enough to get us home. At that point I replaced all the plugs and wires, put in a new distributor cap and rotor, changed out the pcv, air filter and fuel filter. It ran just fine after that. That was until a bit over a week ago.

Then it started all over again. This time the check engine light started flashing, code 32 and 45, there was a combination of gas and rotten egg smell coming from the exhaust, it was a mess. I found through this forum that the egr valve could be cleaned and I did that, code 32 gone. I also checked and cleaned the IAC valve, replaced the MAP sensor, and rechecked for vacuum leaks again. After that I took it for a test drive and it felt like it was trying to pull and ten ton rock but as I got up to about 20 or so mph the thing just smoothed out and took off. It ran fine up around 50-60 mph, but ran terrible back at idle and on acceleration.

I was looking around one day and for no real reason pulled the vacuum hose off the back of the intake manifold, well, I noticed that the idle smoothed out and when I took it for a drive without that hose connected it ran better, not great, but didn't bog down on acceleration and ran okay at speed. I was thinking becuase of the code 45, engine running rich that for some reason the engine was not getting enough air and I thought it might be the manifold valve. I doubt it at this point.

So, this a.m. I went out and did a few more checks. First I hooked up my vacuum gauge, actually its the mercury type, and its reading 32 inches with a slight fluctuation up to 32.5.(although the manual says it should be 17-22) if I rev the engine it spikes, drops down to nothing and then back to 32. I checked the oil for gas. There is a slight odor of gas in it. Although I really don't know if gas in oil shows up like water does, so I honestly don't know what to visually look for. I pulled the plugs and they do not show any carbon fouling like I would expect for a rich mixture. There is one more thing that I noticed as well. When I open the throttle I hear a sort of gasping, sucking air noise coming from the throttle body and it appears to be coming from the small hole in the bottom of the intake just before the butterfly valve.

The symptoms are still pretty much the same, rough idle, hard starting, bogs on acceleration and a very strong gas smell. I don't have a fuel pressure gauge that I can check it with, so if the injectors are leaking I will need to go by eveluating the condition of the oil, or just pull the plenum and take a look.

So, there we have it and I am open to any further suggestions as to where to go from here.

Thanks

 

I would start by unplugging the 02 sensor. If it runs good, replace it. The computer will default to a preset readings and it will get horrible gas mileage.

 

Found the connecter and unplugged the O2 sensor. Made it run even worse. Still hear that kind of sucking,gasping noise.

Thanks

 

I'm starting to lean more and more towards a leak in your CPI unit. The only way to diagnose this without pulling the upper manifold would be with a fuel pressure gauge. Advanced Autoparts should have one for around $45 (Click HERE). If you don't want to spend that kind of money, I think you may be able to "rent" a fuel pressure gauge from Advanced or Autozone. You just pay them the price of the tool and when you return it you get your money back (IIRC).

Another way to tell is if when you 'key-on' (not start) the truck, you can hear the fuel pump whirl. It should shut off after a bit. If you leave the key on and the pump turns off then comes back on again a short time later, you have a leak in the system somewhere.

You really need to get the fuel pressure tested and let us know where it's at. If you are under 55psi, you'll have issues. If it jumps up to 55psi, then slowly leaks down after you turn the key off, then you've got a leak. I spent the $45 or whatever $$$ a long time ago for my fuel pressure tester (it was a cheap-o) and it has never let me down and it is one of the first checks I run when trying to diagnose a vehicle problem. So much is dependent on proper fuel pressure.

 

Hi Kyle: I'm kind of leaning that way myself since you told me about it. I do hear the fuel pump whirr when I turn it on but don't pay too much attention to it after that. Gotta go study for my anatomy test for EMT class so I'm done for the day. I'll call O'reilly auto parts in the morning and see if they have a fuel pressure tester they rent out, if not I am just going to yank the plenum and take a look, doesn't seem too difficult. plus with as many miles as this has, it probably wouldn't be a bad idea to check anyway.

By the way, that gasping sound is coming from the idle air valve inlet off the throttle body. I did an Ohms check and its in spec but something just doesn't seem right about it, I don't recall it ever making that kind of noise before when I was working on the motor.

Anyway time to hit the books. Thanks again.
Geoff

 

Might be your whole problem.

 

I have a quick question about the '94 engine... Does it use an inline Mass Air Flow sensor? If it does, are you trying to get this thing to run right with all of the air ducting hooked up properly or with it off? The reason why I ask this is because my bravada will barely run at all if I don't have the air intake on (which has the MAF in it). If the computer senses that little to no air is being drawn into the engine, it will run like garbage! If it does use a MAF sensor, you might also want to look into cleaning the elements. Some electrical parts cleaner should do a good enough job of cleaning the elements off, but if you think you need more, you can soak a q-tip into the cleaner and then LIGHTLY wipe the elements, but be VERY careful as they are just thin wire that can break off and ruin the sensor.

As far as the gasping/weezing sound coming from the throttle body, without hearing what you are experiencing, I cannot say if it is normal or not. I can say that some noise is normal for a throttle body. It is just the sound of the air passing through the idle air circuit. Does the sound change independently of the RPM?

 

I am having the same problem with my 94, and I got a weird reading on the Idle air control too. I replaced it and it still does it. This one has me baffled. I have checked the usual culprits, and my truck isn't throwing a code. I am about to pull off the intake and clean out the EGR passage. That is the only thing I can think of right now. New o2 sensor, new EGR, (both were actually bad, I did not just replace them) The only vaccume leak I have is my heater control switch, and it is so small it is negligable. If you guys figure this one out keep me posted.

 

As far as I can figure from the manual, it does not have an MAF. It has a temp sensor in the air duct going to the throttle body and a MAP sensor in the plenum. I sat in the truck the other day and turned on the ign switch and I can hear the fuel pump kick on. So, I sat there for the better part of an hour and I never heard it kick on again. Its kind of hard to describe that noise coming from the throttle body, but its coming from the channel that leads up to the IAC valve. I am beginning to suspect that even though it is checking out okay on the ohms test, the pindle iteslf may be binding and not reacting as it should. I can stick my finger up through the channel and push on it and it takes a while for it to re-adjust itself.

Thats not saying that I couldnt still have a fuel leak or a number of other problems. Its just finding them. I had a Lumina not long ago and just past 100K everything went belly up, including the intake manifold gasket which promptly allowed the contents of the radiator to flow into the oil pan. Not pretty.

Gonna keep pluggin along, and thanks for all your help.

Geoff

 

OK I fixed it! On the bottom of the intake pipe, there is a sensor in the rubber elbow right before the throttle body. If it is no good, or in my case unhooked by a careless oil change guy at wal mart[:@] it wont throw a code, but the engine will show the signs you listed. I replaced mine for $13 at autozone, and my truck purrs like a kitten. (the only reason I had to replace it was it was hanging, rubbing against the belt by the wire) Since you have to remove the airbox\tube to change the filter, I may just change my own oil from now on. I obviously cant trust the guys at wal mart.