Rough blazer when cold stumps 2 auto mechanic stores!

[mrbubbs]

About a week ago, I started my '92 Blazer with 152K miles on it and it ran really rough when idling. Putting the car into reverse made the engine run even worse and as I started to roll in reverse, the engine stalled out. I was already late so I started the car and just accelerated through, and after
15 minutes of driving or so, the car smoothed right out and acted perfectly.

A couple days ago, when starting the car, the same symptoms happened again. This time, a little more extreme with the inability to want to run and maintain a speed down the road. I also started getting a few backfires.

I took the car into a local repair shop and they said the fuel pressure was only 45 lbs or so at an idle. They made sure to complain that it was the original fuel filter and that it was rusted on but they eventually changed the filter. The mechanic test drove the car after changing the filter and said the car was running much better. When I went to pick up the car, the car was sitting for a few hours and did not want to run still! The mechanic told me the filter was really clogged and it may be some bad gas still. I asked the mechanic if he even checked the fuel pressure after or during replacement of the fuel filter and his facial expression indicated that he thought that would not be very helpful or that it wasn't possible for him to do at the time. This seems like awful logic when trying to diagnose a problem. I was reluctant but I took the car home to try to figure out if I wanted to get drastic with this shop or cut my losses and go elsewhere.

I called the same shop the next day and they said they weren't sure what to do next, but it could get expensive! They said the fuel pump might be at fault. I had become fed up with the small shop that seemed like a rip-off place. >:E The guy acted as if the car is just too old and there's not much to do short of putting about $1200 into it. That's nuts! Somehow, I don't think the car needs that much money to fix it. It drives like a dream when it is warmed up.

I decided to call up a different mechanic shop, this time, a large chain, and they diagnosed the car but I had already driven it for approximately 15 minutes to get there and the car drove crappy at first but then smoothed right out! The service engine light came on too.

After a few hours, I called the 2nd shop and they said the car was driving great and weren't sure what to do. They told me it's possible it's a fuel filter but they wanted to make sure what it was before they started changing parts. Well, at least this is better than the last shop.

Tomorrow, I will be calling them up and see what the verdict is after they get a chance to examine the car when it is running crappy; that is, when it is first started in the morning. With a new fuel filter replaced by the 1st shop, the 2nd shop said the fuel pressure was at about 56lbs or so during idle, so I'd think a fuel pump is not at fault.

There is a chance the plugs might be getting old and I did see some oil residue near the PCV valve but I was able to blow through it pretty easily. I have never missed an oil change but I unfortunately had the same fuel filter on for at least 75K miles. I was able to pull the code out before taking it to any of the 2 shops and the code was for an electronic spark control (knock sensor, I believe). This might be the problem but I don't have the car now to check.

I really suck at working on cars but getting a little more knowledgable, I guess. Any ideas on what could be wrong? I suppose I'll find out tomorrow!

[ricksza]

If the fuel filter was that bad, why would it get that much better when hot? If it was that bad, it would run bad under full throttle hot also.
When you start it up, does it blow out a lot of blue smoke? Could be valve stem seals leaking and giving the plugs a hard time.

There was a concern a few years ago about gasoline deposits forming on the valve stems. It would harden on the the valve stem and tighten it as the engine got cold, then when started, the heat would soften the deposits and the valve would move free again. We used GM's top engine cleaner to help clear that out.

There is also this Service Bulletin to run pressured cleaner through the injectors:
No Start, Hard Start, Rough Idle After Start (Clean CPI Poppet Valve) #99-06-01-022 - (Dec 21, 1999)

[BlazerLT]

Sounds like the EGR valve is plugged open or the CPI injector is shot.

Is this the CPI engine?

[BlazerLT]

Sounds like the EGR valve is plugged open or the CPI injector is shot.

Is this the CPI engine with the orange lettered vortec plate on top of the engine?

[mrbubbs]

Originally Posted by BlazerLT

Sounds like the EGR valve is plugged open or the CPI injector is shot.

Is this the CPI engine with the orange lettered vortec plate on top of the engine?

Thanks for your replies!

Honestly, I am not sure. The car is also at the shop or I'd check. The engine definitely has the orange Vortec lettering on top. I wish I could remember the VIN as I think that designates the injection type? I am probably wrong on that, though.

To the other reply, I would say it has a little bit of gray smoke but not blue.

It's at a shop right now and they are having a hard time keeping it running, so I guess at least the symptoms show up for them now as I have experienced instead of "running just fine" as the case was yesterday before they kept it overnight.

[blazee]

At 56 psi it would have to be CPI.

[BlazerLT]

For about US$350 you can put in a new injector and nut kit and new upper plenum gasket and clean the EGR and have a new engine again.

[mrbubbs]

I can confirm that it does has the CPI type injection. I think I may heed BlazerLT's suggestions. Again, thanks to those who offered their input on my problem! The shop wasn't able to get the car to run crappy, even when cold after leaving it overnight at the shop. So I'm pretty stumped.

[BlazerLT]

Remove the top vortec name plate, then remove the IMTV valve under it noting how it is orientated, then take a flashlight and look down into the upper plenum and smell for fuel , washed golden spots and pools of fuel.

Also smell you oil dipstick and smell for gas.

You will smell it if it is there and the oil will be very thin.

[blazee]

Was the code you pulled 43?

If so this may help:

http://www.syty.org/old/d&e-code43.html

[mrbubbs]

blazee.. yes, that's the code and the link was helpful.. I'm not sure if the problem is the knock sensor or what.. I don't have the car at the moment to test anything. Will let the thread know what the diagnosis is from the auto shop or by me figuring out the problem when I get the car back, so the answer can be archived.

[BlazerLT]

Originally Posted by mrbubbs

blazee.. yes, that's the code and the link was helpful.. I'm not sure if the problem is the knock sensor or what.. I don't have the car at the moment to test anything. Will let the thread know what the diagnosis is from the auto shop or by me figuring out the problem when I get the car back, so the answer can be archived.

Too bad you didn't hold on before you threw it into the shop, we coulda saved you some money.

[johnpsu]

Its probably the cpi and fuel lines gone bad or the EGR. The knock
sensor(s), may still be bad but they it wouldnt do that. When the
code is set for a bad sensor the ECM automatically refers to a retarded
timing table, and from what I understand it doesnt use the knock sensor
readings. Besides even if it could cause it, it wouldnt go away when
warmed up. Id say maybes its the Cpi or fuel lines, when its cold the
orings either on the inlet/return fuel lines, or on the fuel pressure
regulator contract, and then expand with the heat... thats my bet, I
know this sometimes happens with pnuematics in the cold

[mrbubbs]

Ok, great...
Goodyear says it's the fuel pump.. they get the tank off, they complain about how rusty everything is.. they apparently broke a fuel line because it was so rusted (dunno) and now they say I need to pay $450 more for a fuel sending unit. How much can this part be worth? I am trying to look at some parts stores online but I am not finding anything. It's for a 1992 Chevrolet Blazer 4.3L CPI, I can't believe this!

[BlazerLT]

Did you tell them what to check?

You can't blame them for looking at the fuel pump because that is where they would look first.

And the sending unit being rusted is quite normal.