***92 - 95 CPI Engine Info.***

[blazee]

You have probably reached this thread either because you found it while searching or someone provided you with a link. This thread is intended to provide information about the common failures of the 95 and older VIN “W” 4.3L V6 CPI vortec engines.


1. Fuel Pressure

These engines require a lot of fuel pressure. The fuel pressure spec is 58 – 64 psi. This unit needs the upper end of the fuel pressure specification (64 psi) to operate correctly and have 64 psi at the injector to correctly fire all six nozzles at 43 psi. Sixty to 61 psi is the minimum to run this engine correctly (key on engine off). The engine will operate slightly lower pressures, but there will be drivability issues.

The fuel delivery changes quite a bit with just a slight change in pressure, the unit flows 28% less volume at 55 psi compared to 60 psi. When testing the fuel pump you should see 58 – 64 psi with the key on, engine off (KOEO), this pressure should hold fairly steady after the pump shuts off. If it bleeds down quickly, then there’s a problem. The pressure should be 52 – 54 psi with the key one, engine running (KOER). The pump should be drawing a minimum of 7 amps and should pump a volume of about 1ounce per second. If low fuel pressure or volume is detected it should not be assumed that the pump is bad, it could be caused by other things such as the fuel pressure regulator or fuel filter.

2. The Injector Assembly

The assembly uses a single low impedance (1.5 ohms) "maxi injector" that distributes fuel simultaneously to six poppet nozzle assemblies. The injector controls fuel flow based on PCM command. A 20 micron final fuel filter basket filters the fuel entering the injector body. The injector is rarely the problem, however, it is attached the fuel pressure regulator, which fail regularly.

The fuel pressure regulator is mounted within the manifold and must respond to a biased manifold pressure against actual fuel pressure. Excess fuel is returned to the fuel tank through the fuel return line. The regulator itself has been a major "pattern failure" unit with units failing daily. These regulators will leak and cause fuel to blow out the regulator vent hole creating a very rich mixture on one bank (passenger side) of engine. It is not uncommon to have a regulator leak come and go with the unit leaking one minute and holding pressure the next.

Fuel pressure testing as previously mentioned is a must with these units but regulator leakage may be somewhat intermittent. A tip is to check fuel pressure with the gauge while looking for a quick leakdown.
Another short cut is to remove the IMTV (Intake Manifold Tuning Valve) from intake manifold. Once the IMTV unit is removed, visually inspect the inside of intake manifold. The manifold and injector unit should be very carboned up and dirty. Any clean areas indicate a fuel leak internal to the manifold plenum. Most times this is caused by the fuel pressure regulator leaking fuel from vent hole in the regulator body.
Other factors may be present (such as a cracked inlet fuel line) but usually the regulator unit has failed.
If no leak is detected through the IMTV hole, but a faulty unit is still suspected then you must pull the upper plenum to get a full view of the inside of the intake.

If the assembly is bad then it must be replaced. A bad leak will dump so much fuel that it will get into the oil and cause engine damage. It is recommended that the CPI and Nut kit be replaced at the same time.

Below is a "how to" that was originally posted here:
http://www.s-seriesforum.com/forum/s...threadid=34659


1. Remove the air intake duct from the throttle body
2. Unplug the IAT sensor mounted in the duct, get the whole thing out of the way.
3. Remove the VORTEC top cover (2 Torx bolts)
4. Disconnect the vacuum hose directly under the throttle body.
5. Disconnect the MAP sensor on top
6. Disconnect the internal air door actuator (top center of the intake)
7. Disconnect the IAC (idle air control)
8. Disconnect the vacuum hose at the rear passengers side, next to the distributor.
9. Remove the bolts/nuts holding the coil bracket on. swing the coil out of the way.
10. Remove the nuts/bolts holding the wire harness bracket (driver's side)
11. Remove the throttle cable guide loop from the right rear stud if it has one. Leave the cables and bracket on the intake.
12. Blow everything off with compressed air.
13. Disconnect the vacuum hose at the brake booster, you should be able to fish it through the plug wires and leave it attached to the intake.
14. Remove the nuts/bolts/studs around the perimeter of the upper intake. Try to note where studs go, and where bolts go, there are different lengths too.
15. Lift the upper intake straight up, flip it over, and lay it down somewhere over on the passenger's side, near the blower motor. i opted to just take mine all the way off and out.

This is when you will see excess fuel that leaked from the regulator into the intake on the passenger's side. Next be careful to check for big carbon chunks stuck to the gasket near the EGR valve. Suck them out with a shop vac.

16. Disconnect the injector electrical connector.
17. Remove the plenum gasket. this can be difficult since it’ll crack. carefully use a small screwdriver or the like and scrape towards the OUTSIDE of the plenum. don’t want of those little pieces falling in there.
18. Disconnect the fuel lines inside the intake, by removing the retainer clip (pull it straight up) cover with a rag, there may be pressure in there.
19. Carefully remove each individual poppet nozzle by squeezing the clip on it and pull straight out of the intake port. Be careful the plastic clips are very brittle and break easy.
20. Lift the injector (with poppet nozzles) out.
21. Replace the injector in reverse order, make sure to use new "O" rings and retainer clip on the fuel lines. Put a small amount of oil on the "O" rings to help assembly.

Change the oil and filter because the gas may have washed down the cylinders into the oil (bad).

Here are some great pictures:
http://www.automotiveforums.com/vbul...d.php?t=473110

[BlazerBoyLT98]

Awesome post! Great Job with that post. Now write one up for my truck! haha just playing! I am sure a lot of people are going to benefit from the post you just put together. Great Job!

[blazee]

Thanks, I hope that it helps someone. I'm going to try to make threads explaining all the common problems that we see in the forums.

BTW... I've already made one for yours. It's more of a rough draft of some info that I found at I few sites. I'm planning on redoing it soon.
http://www.automotiveforums.com/vbul...d.php?t=450484

[BlazerBoyLT98]

Originally Posted by blazee

Thanks, I hope that it helps someone. I'm going to try to make threads explaining all the common problems that we see in the forums.

BTW... I've already made one for yours. It's more of a rough draft of some info that I found at I few sites. I'm planning on redoing it soon.
http://www.automotiveforums.com/vbul...d.php?t=450484

Wow never even noticed it! You are the man! Thanks Bud

[cubanlorenzo]

Very nice write-up...........

make Blazee the new MODERATOR!!

[Sen Sen]

GREAT post but, it's should be renamed to:
"Top two reasons why your 1st gen blazer blows A$$"

[s10blazerman4x4]

Only blows ass if you have that injection i dont have that problem with my Z

[wolfox]

I have posted some anecdotal advice in this thread from my recent (yesterday) replacement of my CPI. The truck runs better than when I first got it!

http://www.automotiveforums.com/vbul...=450540&page=5

[leadalto]

Originally Posted by blazee

2. The Injector Assembly

These regulators will leak and cause fuel to blow out the regulator vent hole creating a very rich mixture on one bank (passenger side) of engine.

Another short cut is to remove the IMTV (Intake Manifold Tuning Valve) from intake manifold. Once the IMTV unit is removed, visually inspect the inside of intake manifold.

A bad leak will dump so much fuel that it will get into the oil and cause engine damage.

I'm not sure that the questions I have should be attached to this thread. If not, I apologize.

The problem I'm having is described in my reply to an existing thread found at the following location:
http://www.automotiveforums.com/vbul...49&postcount=4

The questions I have relating to the injector assembly description are:

1. Does a leak in the regulator vent hole go into the plenum or into the manifold? If it leaks into the manifold causing a rich mixture, why do I have to add gas into the air intake to start the engine? If it leaks into the plenum, why isn't there a strong odor of gas with the IMTV unit removed.

2. If there is a gas leak in the plenum, how does it get into the engine oil? The pictures don't show any openings that would lead to the crankcase unless they're hidden in the pictures.

3. Once I get the engine started, it runs very rich, blowing black carbon out the exhaust and hunting for an idle speed. If the problem is not the regulator, could a weak fuel pump result in a rich mixture and hunting? When its running, the fuel pressure is centered around 50 psi and the pressure guage needle is vibrating. Pressing the accellerator pedal sharply makes the pressure jump to over 65 psi before settling back to 50 psi.

[leadalto]

I forgot to mention that because I could get starts by flicking the key, I removed the ignition switch (with great difficulty) and took it apart. It looked like there was a burned spot on the conductor bar associated with "ignition on". Replacing it with a new one did not cure the starting problem.

Please, can anyone answer some of the questions from my previous post?

Any help will be greatly appreciated!

[Cailen]

I think there might be some confusion about what the plenum is and what the manifold is. The plenum is just the piece covering the intake manifold. Nothing will ever leak in to it, because it is above the manifold. The plenum is what gives our engine the "Vortec" name, as there are several different pathways that the air can travel through (long or short, depending on the RPMs) before being forced downwards. Assuming you do in fact have a leaky regulator I'm not sure why you wouldn't smell fuel with the IMTV off.

If fuel is leaking from your regulator it can seep down in to this area, which is directly below your intake manifold:



Where I've noted "remove carbon" is another area where raw fuel dumpage can cause problems: the EGR system. If you had looked at that hole up close before I cleaned it out I was at about 30% flow.

And no, a weak fuel pump could not cause these problems. How does it look inside the manifold?

[leadalto]

Originally Posted by Cailen

I think there might be some confusion about what the plenum is and what the manifold is. The plenum is just the piece covering the intake manifold. Nothing will ever leak in to it, because it is above the manifold. The plenum is what gives our engine the "Vortec" name, as there are several different pathways that the air can travel through (long or short, depending on the RPMs) before being forced downwards. Assuming you do in fact have a leaky regulator I'm not sure why you wouldn't smell fuel with the IMTV off.

If fuel is leaking from your regulator it can seep down in to this area, which is directly below your intake manifold:

Where I've noted "remove carbon" is another area where raw fuel dumpage can cause problems: the EGR system. If you had looked at that hole up close before I cleaned it out I was at about 30% flow.

And no, a weak fuel pump could not cause these problems. How does it look inside the manifold?

Cailen, Thanks for your help!

When all else fails, read the instructions. In this case I have a Chilton’s that has an exploded view of the Upper and Lower Intake Manifolds and the CMFI system components. Nowhere in the list of components is there mention of a “plenum”. I was using a general definition of a plenum as being an air-filled space in a structure. The space that I am referring to as a plenum is the top part of the Lower Intake Manifold.

The intake structure according to Chilton’s is a layered assembly where the Upper intake manifold is the assembly just under the Vortec cover plate. This assembly contains the throttle body, Intake Manifold Tuning Valve (IMTV), Manifold Absolute Pressure (MAP) sensor, Idle Air Control (IAC) valve, and has the curved air tubes characteristic of the Vortec system.

The Lower intake manifold contains the Exhaust Gas Recycling (EGR) valve, fuel pressure regulator, fuel injector, 6 poppet nozzles, the “nut” assembly (fuel intake and return lines). Pictures showing the top view of this assembly with the Upper manifold removed are shown in the “how to” section of this forum. As I mentioned above, this is what I was referring to as the “plenum” right wrong or otherwise.

The picture included in your post is looking at the head intake ports which are underneath the Lower intake manifold.

I have found forum posts which contend that gas from either a leaking fuel pressure regulator or the fuel lines gets into the crankcase. These items are in the Lower intake manifold. Based on the pictures of this assembly posted at this forum, I don’t see an opening where the gas could seep down into the head intake port area. If there is an opening, it doesn’t show in the pictures. Also, there was some mention that a leaking regulator would cause a rich mixture on one side of the engine. Again, how does this gas get to the head intake ports.

If there is raw fuel dumpage into the head intake port area as you mentioned, would it be coming through defective poppet seals or stuck open poppet valves?

The only thing I’ve done so far is to measure fuel pressure at the Shrader valve. In reading the various posts, I think I have a chicken an egg situation of either a bad fuel pump or fuel pressure regulator. But, I don’t think I have a leak because I don’t smell gas when the IMTV is removed. Is it possible for the pressure regulator to keep the dynamic pressure low enough so that the poppets won’t spray gas during cold start but with the engine primed will maintain gas flow when the voltage is slightly higher? I have a new battery and have kept it fully charged. I’ve read several posts that say the fuel pump is very sensitive to voltage if it’s worn out.

Maybe it’s more than one problem? I can start it by priming but it does not run well. I had an EGR code several months ago and after cleaning some carbon flecks that kept the valve from closing, it ran well. Then the hard or no start situation developed (gradually). I have not seen the CES light come on which happened the last time the EGR was stuck.

[leadalto]

Originally Posted by leadalto

I have not seen the CES light come on which happened the last time the EGR was stuck.

I meant the Service Engine Soon (SES) light. The last time I started the engine was several days ago. I did not have to prime it but it took at least 6 or so trys to get it going. I ran it up and down the hills in my neighborhood until it warmed up. It ran like crap the whole time and wanted to die about a block from my house. During this time the SES light did not come on. This morning, I shorted pins A and B of the ALDL/DLC connector and checked for diagnostic codes. Nothing appeared other then code 12.

Then I started the engine which took about six tries (In between tries I turned the key on several times to maximize the fuel pressure at the Shrader valve). Again, the engine ran very badly with soot coming out of the exhaust pipe. I did not drive the car but just ran it in place until it started to warm up. No SES light came on and just as I was about to give up, the light popped on. The code was 32 Exhaust Gas Recirculation (EGR) system. I don’t know why it didn’t set before or took as long as it did this time. I’m guessing that it might have something to do with Open/Closed loop operation or waiting for the oxygen sensor to stabilize.

Based on past experience with the EGR valve, I’m guessing there are black flecks of carbon keeping the valve from closing. The first time this happened (about 5 years ago), there was no problem running at freeway speeds but it would die at the end of an off ramp because it would not idle at all. This time it idles after a fashion but it’s also not running well at higher speeds. There is probably something else that’s not right but I’ll take a look at the valve first. I’m guessing I might have to do a serious cleaning job of the EGR passages.

[Cailen]

Terminology can be our worst enemy sometimes.. you gotta love it.

This first picture shows the symptoms of a leaking fuel pressure regulator. I'd imagine a P0172 or P0175 would be caused by fuel leaking past a poppet seal.

http://i15.photobucket.com/albums/a3...rManifold1.jpg


From the picture in the other post you can see I had problems elsewhere. The port with the arrow "remove carbon" corresponds to the smaller port on the opposite (drivers) side, and lines up with the EGR passage cast in to the lower manifold. I was leaking so much that I still had raw fuel in my exhaust. You can see how this wreaked havoc on my EGR, and why I haven't felt good about delaying replacing my cat (which I'll be doing in Jan).

Aside from leaking past a poppet, the only other place I can conceive fuel leaking in to the head is through the lower manifold bolts. They don't come with any thread sealer on them from the factory (at least mine didn't have any) and these go DIRECTLY in to the lifter valley.

When I did this job I went to town on both the upper plenum and lower manifold, all EGR ports and passageways, and I even cleaned up all the sensors (save the coolant temp sens and o2 sens').

o2s will have to wait until after I get the catback + muffler, but they're next priority. As you can see by the pic of the lifter valley I spilt a good deal of coolant!

ALSO, my plugs we're fouled to shit! I can't blame this solely on the leaking regulator though... the previous owner was using bosch 4s! How's that big chunk of carbon for ya?

[leadalto]

Originally Posted by Cailen

Terminology can be our worst enemy sometimes.. you gotta love it.

Amen. I would have liked to show the exploded view of the upper/lower manifolds and the CMFI components as shown in Chilton’s but I’m not sure it’s legal since it’s copyrighted material. It’s a moot point since I don’t know how to show graphics with my posts anyway.

Originally Posted by Cailen

Aside from leaking past a poppet, the only other place I can conceive fuel leaking in to the head is through the lower manifold bolts. They don't come with any thread sealer on them from the factory (at least mine didn't have any) and these go DIRECTLY in to the lifter valley.

My bet is on the poppets. This is only an opinion since I haven’t yet disassembled my manifolds, but, it looks in the pictures that the poppets are held in by a retainer which is not necessarily sealed. Since their holding sockets are slightly elevated, it would take a bit of gas before it would leak through. Nevertheless, whichever way the gas leaks out is a good thing otherwise you would end up with a mini gas tank on top of your engine (not good).

Originally Posted by Cailen

When I did this job I went to town on both the upper plenum and lower manifold, all EGR ports and passageways, and I even cleaned up all the sensors (save the coolant temp sens and o2 sens').

If you saw my earlier add-on to the thread, I’m going to tackle my EGR next and I hope I won’t have to do a major EGR cleanup.

An aside: Today, my aging Buick Park Avenue water pump took a crap so I’ll have to do it first since my golf clubs are in the trunk. I’ll get back to the S10 Blazer after that. My wife says I should get rid of all my old cars and replace them with one good new one. I didn’t know she had such impeccable logic!

But, how am I going to get rid of a Ford Model-T which is just a pile of parts taking up space in my garage and my first “new” car, a ’69 Mercury Cougar waiting to be restored for the last 15 years, without experiencing great stress.