Hey all - I'm new to the 'Forum' and glad there is such a thing. I'm sure others have asked and received good answers about the symptoms I'm having but I can't find the right thread to answer the questions I have now. So at the risk of repeating someone else I'll ask anyway.

Since the weather has gotten colder here in VA (maybe the last 4-5 weeks), my 95 Blazer idles really rough in the morning, bounces like a cylinder is not firing and flashes the SES light for several minutes. As I drive, it is sluggish to want to accelerate and on my way to work (about 10 min) even after going solid, the SES sometimes flashes again for a minute. The engine runs smooth during the day and afternoon drive home and often the SES light goes out, only to come on again the next morning with the same symptoms.

Last week my shop pulled 3 codes from the computer, (O2 sensor, random misfire and something regarding the EGR valve). My mechanic thought an EGR cleaning and new filter/gasket were needed so we replaced them. Still had the problem. Today they let the shop guru check it out on a more expensive scanner and he pulled three codes. This time I asked for the exact codes: (P0141 O2 Sensor Heater Circuit (Bank 1 Sensor 2), P1133 HO2S Insufficient Switching Bank 1 Sensor 1, P0300 Random/Multiple Cylinder Misfire Detected).

He says he suspects a fuel leak from the fuel injector system; says this is a common Blazer problem and estimated the repair to run $1000. Reading some posts by knowledgabe people online this evening I have heard that my mechanic is correct in that leaking fuel injectors do affect Blazers (BlazerLT from another site seemed quite knowledgable). However, I am still skeptical how that problem causes the symptoms I'm having. I would think if fuel was leaking I would experience problems more consistently and not just in the morning. Is warmer weather masking the issue? I like my truck and want to fix it but, like many people are on a tight budget and want to be sure every dollar is spent wisely and addresses true root cause. Parts-changing shops are a pet peeve of mine and my wallet.

Can anyone explain if and how these codes and my Blazer's symptoms match the diagnosis of leaking fuel injector system? I would appreciate any good information or a direction to look for more information. Thanks.

 

I believe that your system for the '95 model year was CPI (Central Port Injection). If that is true then this system has three items that might leak:

1. The "Nut Kit" are the fuel lines under the upper intake manifold that supply fuel to the injector spider, they are plastic and generally leak at the connections at the spider or the back of the intake.
2. The fuel injector fuel distribution spider. It has a single fuel injector that pressurizes the outer poppet valves. This unit may leak at the individual injectors either at the fuel metering body or at the poppet valves.
3. Fuel pressure regulator (most likely) will leak at the connection to the fuel meter body.

These allow unmetered fuel to gather under the upper intake manifold and be sucked into the cylinders without the computer allowing extra air in to adjust the air/fuel ratio correctly. This will make the O2 sensors work harder and they send the signal to the computer to make adjustments then the computer tries to but since there is unmetered fuel in the intake it causes rough idle and if it is going away when warm then I think that it would indicate that the leak is not large enough that when the computer compensates for the operating temperature (closed loop computer) it tends to offset the extra littel fuel that affects the cold (open loop computer) operating settings...

The PO300 misfire is related to the fact that the computer is unable to compensate. It will set a SES light temporarily when the misfires occur. If the misfires don't happen like when the engine warms up then the light stays off. But until you fix the rough idle condition the light will come and go...until the computer reaches a point that will set the code/light permanently.

 

Thank you 20Blazer00 for your response and time. Based on your answer do I understand that you are thinking the most likely cause is the fuel pressure regulator leaking?

Your explanation of possible causes and how it happens confirms what my mechanic told me about the three areas where it could be leaking and why it is a problem for the computer. He said the first step to find out whether this was the cause and where the specific problem is, was to remove the plenum lid and then he would be able to see whether the nut kit needs replacing or the distribution spider. He said the fuel pressure regulator is contained within the spider body and would also require its replacement. What are the specific names for these parts and/or GM part numbers? I want to look them up online.

What is particularly strange to me, and what I failed to mention in my initial post - for length reasons, is that since I bought my 95 Blazer in 1999, it had always been giving me a rough idle on cold mornings and giving the O2 sensor code. I got tired of paying for scans only to find the same code and no apparent detriment to the vehicle. However, two winters ago I decided to push my mechanic (same guy as now) for a solution. At that time he tried replacing the thermostat, thinking that the temperature signal it was sending to the computer on cold mornings was wrong, causing the wrong fuel/air mixture when cold. He replaced it and miraculously the symptoms disappeared......until this fall. Because the symptoms are exactly the same it made me think initially that maybe my thermostat was bad again and that would fix it. The multiple codes now makes me think that it is likely something more.

Anyway - thanks again 20Blazer00 for your time. Any more information you have regarding this will be appreciated as well...especially if you know the names or part numbers of the components I might need to replace. Thanks again.

 

20Blazer00 has replied with an excellent post. The only other thing I can think of is the coolant temp sensor operation. If you have a sensor that is out of range it can send the wrong signal to the computer and then the computer keeps the injectors open to long, causing over fueling.
20Blazer00 is probably right, but it's worth checking the coolant temp sensor.

 

I had pretty much the exact issues in my '95, plus i smelled fuel pretty heavy, especially in the morning when it was cooler. I had a friend get me wholesale for about 270 or so (2-3 years ago). It took me about 45-60 minutes and I'm a chicken/novice. I never had the issue again. After some research I found that this is an extremely common problem that Chevy knows about but they fail after warranty so it appears they could care less. The Haynes manual is very helpful as far as the procedure for changing it. The dealer wanted to charge me around $850 or so to do it so I started researching it myself and figured it didn't look too bad.

Good luck.

 

I had the same problem with a 94 Sonoma. It was a bad CPI unit. I bought a new one with gasket and lines for around $300. It's not that hard of a fix. If you need help let me know and I can walk you through the procedure. You should be able to do the entire job in a couple of hours tops. Come to think of it, there was a thread posted on here a while back showing the procedure. One of the Administrators can dig it up for you I'm sure.

 

Thanks thogbert & Brian for your posts. Based on everyone's comments and especially my mechanic's I decided to buy my own parts and have the shop do the work. Honestly, I'm not brave enough to attempt the fix myself nor do I have any real tools to do the job. I found the parts online, ordered and received them for about $350 including shipping and my mechanic quoted me $150-200 for the labor. Nice to be in central VA, eh? He confirmed I got the right ones and will replace my CPI unit and intake lines tomorrow the 11th.

I bought the CPI unit remanufactured from APN in California and if I return the removed CPI unit in rebuildable condition I get $100 core charge back. This would mean the repair would end up about $450 or less when he originally quoted me $1000 for everything. It pays to get your own parts. I'll post a follow-up to let everyone know how it goes after the fix.