I have a 1995 4.3L 4 door blazer with 212K miles. My check engine light comes on from time to time. My problem is that I have trouble starting it every freaking time I start it. By trouble I mean I have to crank it 10+ times. If it is warm, maybe 5 times. It sounds like it is not getting fuel. For a while, it would not start at all, period. I changed the fuel filter. Did not improve. Took it to the mechanic cause it would not starte, fearing I would need a fuel pump (did not hear when turning key half way). He says for him it started up after a few cranks.He did not have any problems with it. He says I need new oxygen sensors. He said I would need 4 of them. He said my sensors are allowing to much fuel into the engine. I did not have him do it cause I thought I could figure it out. I have been unlucky there. Curious though, can anyone explain to me how to install O2 sensors on my truck? Does the standard maintenence manual at the store provide instructions? Or maybe someone could give me a link to somewhere explaining it?

p.s. I am not a car genius, so if you want, you could dumb it down a little if necessary.
I changed the spark plugs and wires yesterday at the recommendation of the mechanic.
I tried searching this forum and couldn't find a post about this.

 

First thing, I believe your vehicle has 2 O2 sensors, but possibly 3 depending on what part of the model year your truck was built, for your mechanic to recommend changing 4 of them for a no-start or hard-start issue is simply highway robbery. Next, if you have 3 sensors, the two rear most sensors (on either side of the catalytic converter) have nothing to do with fuel delivery what so ever. They are emissions monitoring sensors only. The upstream sensor, the one closest to the engine where the two down tubes come together at the 'Y' in the y-pipe, is the only sensor which has any bearing on fuel delivery. To determine how many O2 sensors you have, simply follow the exhaust from the exhaust manifolds on the engine, down to behind the catalytic converter, counting the number of sensors there are.

Now, onto your problem. Have you tried turning the key on for 10 seconds, off for 5, then on again for 10 seconds before cranking it over? This would serve to prime the fuel system which may be a sign of an internal fuel leak in the engine. Once the engine is running, does it hesitate or run poorly?

Typically, a failing or failed O2 sensor will result in a steady check engine light and your mileage will suffer and the engine may run poorly.

The first thing that you need to do to help us, help you, is to have the codes read on your truck. You should be able to go to any Autozone or Advanced Auto and have them read the codes that are present. Your truck being the in between year as far as PCM technologies goes could make that a bit difficult.

One thing is for sure, I wouldn't recommend going back to the mechanic that told you he needed to replace all 4 of your O2 sensors...

 

"Now, onto your problem. Have you tried turning the key on for 10 seconds, off for 5, then on again for 10 seconds before cranking it over? This would serve to prime the fuel system which may be a sign of an internal fuel leak in the engine. Once the engine is running, does it hesitate or run poorly?"

Yes, I do that. And i will pump the accelerator a few times also.

"The first thing that you need to do to help us, help you, is to have the codes read on your truck. You should be able to go to any Autozone or Advanced Auto and have them read the codes that are present. Your truck being the in between year as far as PCM technologies goes could make that a bit difficult."

Its tough to catch it because it goes in and out, but I will try to do it this weekend.

My truck is not in the best running shape. My other car died (loose oil filter, all but <1 quart fell out, burnt up engine). This truck had not been used regularly for about 6 months. but, when i started using it again, it did not have the starting problem at first. kind of tough to tell if it has gotten worse except for the starting thing.

 

Well, I will add this, the most common problem with a no-start or hard-start condition is fuel supply/pressure. Sometimes it is caused by an internal fuel leak, flooding the engine. Other times it is due to a faulty pump. A fuel pressure gauge (should be less than $30 at your local autoparts store) is a must for determining fuel system problems.

Other things affecting the ability to start the motor would be the ignition system. When was the last time that a tune up was done (plugs/wires/cap/rotor)?

 

Mechanic said he checked fuel pressure and it was fine. Plugs and wires have less than 50 miles on them. cap and rotor have about 20K miles on them. When you say internal fuel leak, would I be able to visibly see fuel drip out? or do you mean a gasket needs to be changed or something like that

 

There are two components inside a CPI motor that typically leak. The 'nut kit' which is the internal lines that run from the rear wall of the intake manifold to the CPI spider inside the intake and this typically is not a problem until someone removes and reinstalls the spider without replacing these internal lines. They do not like to be reused for anything. The other is the fuel pressure regulator located on the CPI spider itself. When this fails, it will dump fuel into the engine, many times making it all the way to the crankcase where it can do some damage if left unrepaired. Both of these conditions would be evident on a fuel pressure leak down test, but maybe not a straight out fuel pressure test that would be done when trying to assess the health of the fuel pump. But again, with a mechanic that tells you that there are 4 O2 sensors, I would double check their work.

 

I will check these things out. Thanks a bundle. you're the man.