Rough blazer when cold stumps 2 auto mechanic stores!

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!

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)

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

Is this the CPI engine?

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?

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.

At 56 psi it would have to be CPI.

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.

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.

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.

Was the code you pulled 43?

If so this may help:

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

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.

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.

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

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!

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.

I am trying to find the price on the sending unit.. Google hath failed me!

You wouldn't happen to know the list price on a fuel sending unit for this blazer? I am having trouble doing some searches on Google for it. I keep getting junkyard prices but I want to know how much one would be for new, basically the maximum I can find it.. and see how it compares to their price (I assume + labor).

You say it is common for the sending unit to be rusted. Is this a function of its location? Is it water that does this or something else? Also, is it somewhat specific to the blazer or most cars in general? I apologize, I am not too versed in parts wear characteristics, especially in the fuel system.

You wouldn't happen to know the list price on a fuel sending unit for this blazer? I am having trouble doing some searches on Google for it. I keep getting junkyard prices but I want to know how much one would be for new, basically the maximum I can find it.. and see how it compares to their price (I assume + labor).

You say it is common for the sending unit to be rusted. Is this a function of its location? Is it water that does this or something else? Also, is it somewhat specific to the blazer or most cars in general? I apologize, I am not too versed in parts wear characteristics, especially in the fuel system.

http://www.partsamerica.com/

http://www.partsamerica.com/

Checked the other stuff we mentioned yet?

From www.partsamerica.com:

Fuel Tank/Sending Units
For vehicle: 1992 CHEVROLET S10 BLAZER 4WD V6 4.3 Liter FI (change)
No parts found.
We could not find any parts that matched your search terms. Please try a different search.

However, I have found a fuel sending unit for about $80 from a place called autopn.com I have emailed them to confirm this is a new part. It seems like quite the difference in price from $450. I guess that's quite a bit of labor and list price markup.

I have not tried your suggestions. I know this frustrates you as I've seen from a few other posts you have replied to for others, but the car is unfortunately still at the shop.

With that said, the auto shop is positive there's nothing wrong with the CPI, that the EGR valve is working and not stuck open, no spark plug issues, timing is good, and they believe the fuel sending unit is the culprit.

They replaced the fuel filter which was quite dirty. They figured as long as the tank was off, they recommend I replace the fuel pump, which I agree makes sense.

Perhaps if I were more brave, I should've done all of this myself. Oh well.

Start calling your local parts stores.

Will do.

If you're looking to verify GM's prices, check this site:

https://www.chevygmparts.com/index.html

Ahh, thanks, ricksza! This helped.

Ok.. the shop replaced the fuel pump and fuel sending unit. They wanted to let the car sit until the next morning to make sure the problem did not reoccur. Well, it did. So today, they have discovered the fuel pressure regulator was leaking into the lower plenum(?) and there was a pool of fuel there, just as BlazerLT had said. :) The dipstick did not smell like fuel at all and the oil looked good. The shop did say they'd take care of the cost for the pump and sending unit and chalk it up to a learning experience for them.

Ok.. the shop replaced the fuel pump and fuel sending unit. They wanted to let the car sit until the next morning to make sure the problem did not reoccur. Well, it did. So today, they have discovered the fuel pressure regulator was leaking into the lower plenum(?) and there was a pool of fuel there, just as BlazerLT had said. :) The dipstick did not smell like fuel at all and the oil looked good. The shop did say they'd take care of the cost for the pump and sending unit and chalk it up to a learning experience for them.


:thumbsup: Congrats on getting your Blazer fixed and finding an honest shop that admits it's mistake and stands behind their work.

That is a place I would go back to.

Ok.. the shop replaced the fuel pump and fuel sending unit. They wanted to let the car sit until the next morning to make sure the problem did not reoccur. Well, it did. So today, they have discovered the fuel pressure regulator was leaking into the lower plenum(?) and there was a pool of fuel there, just as BlazerLT had said. :) The dipstick did not smell like fuel at all and the oil looked good. The shop did say they'd take care of the cost for the pump and sending unit and chalk it up to a learning experience for them.

Glad to have helped you.

Are they going to replace the injector? Might as well have them replace the nut kit while they are doing it.

Unless you are doing all the work yourself.

Hmm... well, the auto shop replaced the fuel pressure regulator. The car still ran poorly after letting it sit for a while to "cool down". They then replaced or rebuilt something about a nozzle, I'm not sure if it's part of the regulator or not. Apparently, it only takes about 1 minute now for the car to run normally without running rough. It is also still backfiring a bit. The shop said they are out of ideas and I said they could keep it over the weekend (again) and they said they'd think more on it and see what happens on Monday. Sucks.

Also.. BlazerLT asked if they were going to replace the injector but they seem fairly adamant that the injector[sic?] was fine. They said they had "ran out of ideas" but it has to be something. I suppose they don't want to run up the tally of the bill they may have to swallow if the part(s) replaced doesn't fix the problem? Dunno. I am sure it is possibly tough to diagnose/repair but it sucks not having my car for over a week and driving a borrowed car around.

Bring us up to date, what is the EXACT problem now.

The problem(s):
1) hard starting almost all of the time
2) runs very very rough when cold.. until about 1-2 minutes of warm-up time.. may be more since they did not let it sit for a day in the cold.. then it may be worse for a longer period of time
3) mechanics are running out of ideas

They have replaced:
1) fuel filter
2) fuel pump
3) fuel sending unit
4a) fuel pressure regulator
4b) "messed around" with the spider

No more leaks in the plenum where there used to be. Fuel pressure quite good. Ignition system tested okay.

Did this problem slowly get worse overtime???? If thats the case it might be your EGR Valve.

replace the WHOLE fuel injector and nut kit.

Not that I mind replacing it.. but what exactly does the nut kit entail? (Is it as obvious as it seems from the name?) Why does this need replacing? Just a "as long as you're in that area" kind of thing, or is it like really needing a gasket when replacing sealed surfaces?

sykopenguin says it may be the EGR valve.. but BlazerLT says fuel injector so I'm confused as to which one to replace (or if both are needed).

clean the egr valve....and check to see if the cpi is leaking.....
Check the CPI injector and nut kit.

Remove the vortec plate on top of the motor and the round valve underneath it.

Take a flashlight and peer down into the hole and look for golden washed spots and pools of fuel.

Remove the EGR valve and check for carbon.

The nut kit is the internal fuel lines feeding the CPI injector.

Often they will become brittle and develop hairline fractures and leak.

Today's update: the auto shop I've taken my car into replaced the spider(?) and is positive the EGR valve is just fine. They are still trying to figure out what the problem is.. the only odd thing they know of at the moment is that the fuel pump voltage is 8V or so.. but it doesn't seem to matter if it is cold (when it runs poorly) or when it has been warmed up for a bit (runs better) and the fuel pressure is 54-56 psi (at idle, I believe). That's all for now.

Fuel pressure should be checked when the engine is off. and the key is on at the first position.

Just got my car back from the shop! The mechanic put an oscilloscope on the TPS and saw spikes in the signal even when the throttle was being held constant. He replaced the ECM and the car's behavior is acting completely normal which I can confirm from past experience. I will let everyone know tomorrow that it positively works when I will start and run the car in the cold (and it is cold in Michigan :)

Thanks, all.

Yes, took it out this morning and was thrashing about in the snow. It works well now. Easy to start, idles nicely, no rough running behavior. Hooray.