Ok, this is a list of noted problem items I have learned about pertaining to the V6 platform. Some of these are things I have discovered myslef, and other I have had many reputable mechanics alert me of.

1. Fuel tank vapor vent valve: The little black cylinder connected to the purge canister. These are noted for going bad, and cost around 42 bucks at NAPA. These are discontinued from GM.
2. The distributor and ignition modules: The ceramic coating cracks on the reluctor coil, and it causes misfire. Also, the rubber O-Ring on the shaft is noted for going bad(even the 3.4L engine has this problem on the 4th gens from 93-95). If your starter is covered in engine oil, and you are leaking, time to replkace the distributor shaft seal. Autozone makes a redisnged distributor for 138 bucks, and it carries a lifetime warranty, with a durable, quality module. Note: Removing the module, will void the warranty on the distributor.
3. Vacuum Lines to the IAC valve: I found this one by mistake, while changing my EGR valve. The plastic vacuum line from the canister to the IAC makes contact with the EGR. The result is a melted plastic vacuum line. I took wiring insulation from a newer GM wire harness, namely the aluminum type, and wrapped a new vacuum line in it when replacing it.
4. Heater control valve: This is a plastic vacuum valve by the smog pump. They are notorious for going bad. They are 17 bucks at Autozone and easy to replace. If your heat is weak, this is where I would start.
5. The oil pressure sending unit: This is the visible sensor, on the lower left side of the block by the oil filter. These sensors are known for failure, which will cause the guage to read all the way up to 80psi, or 0psi. They retail for 7 bucks at AutoZone as well, and are easy to replace.
6. The Exhaust manifold bolts: These engines, including the 3.4L in 4th gens, have machined heads and manifolds. There are no gaskets from the factory installed, and they are not availible through GM. The heating and cooling causes the bolts to snap, resulting in an exhaust leak. Replacement can be difficult, as many of the engines accessory bracket bolt to them as well. Autozone stocks a replacement gasket, which is reccomended for repair, from Fel-Pro. It is a bi-metal style gasket and cnforms to uneven surfaces very well. Which the exhaust leaks and corrosion will make a very uneven surface.
7. The water pump: If you arte losing coolant, and can't find the leak, check around the water pump. Mine is leaking on the lower right side of the block. It was very hard to find the leak, as the hot engine will burn the coolant off. I had a friend with a 4th gen Firebird losing coolant in the same manner.

 

1. How do you know if it is bad? I repositioned the hoses on top of the purge canister because one was squished about half way closed. I do have a lot of vacuum in the gas tank every time I fill up.

2. The entire back of my engine is covered in oil, I think it's because the distributor was loose, I'm surprised it ran as long as it did with the timing being at 0º.

3. Is that the one that goes over the passenger valve cover? mine melted through right above the valve cover.

4. Mine is leaking but I've been too lazy to change it.

5. Replaced it and now the gauge isn't off the scale, it reads 80 psi for a few miles then after the engine heats up it will read about 40 at idle and 80 when I touch the gas.

6. I replaced the bolts on the drivers side then discovered the snapped bolts on the passenger side, that one isn't going to be fun.

7. I haven't checked the water pump because I believe my coolant is only leaking at the heater control valve.

 

I don't know how to test the vapor valve. If they go bad, they can cause excessive fuel vapor in the tank.

If your distributor is stock, then you should probably replace it. I recommend a chilton or haynes manual when doing so. The hold down bolt is difficult to get to, and setting the timing is more complex than a vacuum advance GM HEI distributor setup.

Yes the vacuum line is the one on the passenger side valve cover, next to the EGR.

The heater control valve is very easy to replace. Make sure to use channel locks, or another type of "locking" pliers for the hose clamps. You will need to refill a small amount of coolant in the plastic cap, on the hose coming off of the water pump before restarting the engine. This ensures the water pump is primed, and doesn't get an air bubble. I found out the hard way, by almost overheating my engine, when I replaced my water pump.

As far as the exhaust manifolds, yes it is going to a painful process. You will need to remove the belt tensioner, alternator, and corresponding brackets. You will have to disconnect both head pipes from the manifolds as well. The bolts that are most likely snapped are on your #5 cylinder, under the firewall. These are actuall a stud, with a welded nut on them. Where the head of the bolt snaps flush with the manifold, requires you to remove the manifold, and heat the stud to free the rust, and remove with a set of vise-grips.

As far as the oil pressure sending unit, your car is a 91, and the gauge cluster is electronic. It is possible, witht the age of these cars, that the circuits and stepper motors are finally getting wonr inside the cluster itself. I haven't know these to be a frequent problem, but it is possible. 40psi of oil pressure is fairly normal for the engine's operating range. 60psi would be about the highest it should go, under high reving circumstances.

 

To help w/ problem 2, try using a distributor base gasket for a small block chevy along w/ the o-ring. That should stop the leaking, its a perfect match.

 

Just got to make sure that the oil pump drive shaft and everything is down where it's supposed to be or the second gasket won't do anything (had the dizzy in the hole for a while just barely off of the block but not enough to leak from the o-ring due to some crud or something on one end of the driveshaft for the oil pump).

 

I have a new area to check, when trying to solve the problem with a weak heating system. The coolant inlet tube. This is the black metal tube that comes out of the lower intake manifold, directly under the thermostat.

This is where the coolant goes into the control valve and routes through the heater core. The rubber line with the bleeder cap, is the return line.

To test the line for blockage, you will need to disconnect the line to the heater control valve. Then start the engine cold, and let it rev up. If you aren't getting a face full of coolant, with the engine at 1500+ RPMs, I recommend pulling it off and flushing it out with a hose.

The way to do this is as follows:

1. Disconnect the negative battery terminal.
2. Next pull the serpentine belt.
3. Remove the alternator, and the smog pump(if equipped), and the belt tensioner.
4. There is a tiny bolt that hold the pipe to the back of the alternator bracket. You may need to loosen the bolts holding the bracket to gain clearance for removing it.
5. Remove the upper radiator hose from the thermostat housing.
6. Remove the rubber lines from the throttle body.
7. Press inward and pinch the two plastic hold down clips, with clips pressed down wiggle the tube slowly backwards until it pops out.
8. Do not lose the rubber o-ring that goes on the inside part of the tube.
9. Flush it through all outlets, and in multiple directions.
10. Installation is reverse of removal.

 

You forgot to mention the cheezy plastic clip holding said heater supply tube to the intake manifold adapter... Only way to fix this is to spend $8 on a new manifold adapter and hope your old one doesn't snap on the way out. 2.8's do not have this issue before a certain year (not sure what year but my 87 didn't have the plastic clip thing), but they have something worse, a screw-type fitting that tends to break on either the heater pipe end OR inside the intake manifold.

Also, a number of cars don't have the cheezy spring clamps on the coolant lines but have usual worm screw clamps instead. I'd recommend getting rid of the spring clamps because repeated heating and cooling cycles changes the metallic structure of the clamps, making them weaker.

Next, we have the 2.8's black idle air bypass pipe. This pipe runs from the intake manifold nipple, by the distributor, to the nipple on the throttle body. The rubber ends tend to crack and go bad, and can be replaced with heater hose and clamps. Also, these CAN AND DO come unglued at the joint where the large pipe meets the T. The canister purge line runs off of this T as well as the PCV valve hose connection off of the top. ANY part of this line going bad creates a BIG vacuum leak. THERE IS NO REPLACEMENT FOR THIS EXCEPT HOMEMADE, which requires modification to the rest of the emissions hose system to fit the canister purge line.

Third, we have the PCV parts, namely the grommet in the driver's side valve cover, which tends to become hard with age and not hold the valve properly, creating a leak, the elbow in the passenger's side valve cover with the pipe running to the intake bellows, which may come out of the valve cover or harden or deteriorate, and the connection for this pipe to the intake bellows, which I have seen crack and break. I've wrapped my PCV valve in electrical tape to help it seal to the grommet. The passenger's side valve cover elbow has a replacement that is for V8 cars (I do not have a part number for this, but you'll see it if you go to the parts store).

Followed by the valve cover gaskets, which are notorious for leaking on MANY 60* V6 engines. These not only create an oil leak, but a vacuum leak as well.

I recommend replacing any and all snapped exhaust manifold bolts with studs, as installed on the FWD cars.

Oh, and noticed a bit of misinfo posted here... A 60* V6, having a properly working oil pump and oil pump pressure regulator spring, should be putting out 70 PSI oil pressure, max, when cold, as the spring is calibrated to such. I'd be a little worried if my gauge read 40 PSI... There are commonly 2 oil pressure units on the 2.8, one for the dash (single wire) and one for the fuel pump (2 wire, one being orange and the other gray).

 

Thank you for the intel on the 2.8L engines. They have a little different set-up than the 3.1L does. Yes, the plastic clip is a pain in the butt. The only way to release them is to push the tube in and squeeze them, and hope you can wiggle the tube out of the manifold.

 

I'll recheck the oil pressure, as you are probably right. one more thing on the 90-92 thirdgens. There are two types of oil pressure sending unit. One is a small sender, and is deigned for the oil pressure "Light". By "Light", i mean cars with an oil gauge that shows a red area with and "L" and at the other side a few yellow lines for the normal operating area. Theses sending units are like 7-8 bucks at autozone.

The "Gauge" style is a larger sensor, utilized moreso on the 4th gens, and is desgined for use with 90-92 thirdgens that have a 0-80psi gauge in the dash. This type of sending unit is much more expensive., around 30 bucks.

I found out the hard way, buy ordering the style with the "guage", only to find I had a much smaller sending unit.

 

Yup I know how you feel, i did the same thing in the past. But the oil sensor as 15 bucks at autozone for my 91 camaro.

 

I found a possible solution, for the guys that have V6 thirgens, with the stalling problem.

Let me point out, that some V6's come with an oil pressure sensor. These V6's will stall, if the oil pressure drops below 6psi. Some V6's do not have this sensor. The sensor is designed to cut the fuel pump, and stall the engine, to protect the engine from locking up.

There is one other sensor i found, that may not always code your ECM, yet can function poorly. The engine's electronic "knock" sensor.

This sensor is located directly in front of your starter, behind the smog pump. If you have removed your smog pump, then you can reach it from above. Just make sure the engine is cold, otherwise you'll receive a nasty burn, from the exhaust manifold. Otherwise, you'll need to jack the car up, and reach it from underneath.

The sensor is threaded into the water jacket, of the number 3 cylinder. Try unplugging it, before anything else. Restart your car, and check your idle. You'll notice that the check engine light comes on. It should be a "Code 43", for poor spark connection. "Code 43", for V6 applications, will come up, for only 1 of 2 electrical components. The "knock" sensor, or the ignition module.

Changing the sensor does require draining the cooling system, and applying a thread sealing tape to the threads of the new sensor. The sensor isn't too costly, but it ain't cheap either.

Note, if this sensor is unplugged, the ECM will retard, up to 20 degrees of spark advance to prevent detonation. The ECM will run in "safe" mode, but it can correct a stalling problem. The stalling issue could be linked to over-advanced timing, at idle, yet the sensors voltage range may still be in the "operable" range, so the ECM will not show a code and your "Service Engine Soon" light will not come on.

It corrected my stalling issue, and my overall fuel economy did improve.

My last two fillups, I have averaged over 500 miles per tank. I managed a whopping 514.7 miles, on my first fillup, and 494.3 on my second fillup. These were combined city/highway driving conditions, with some of that driving through the mountains of Western PA.

I may have lost some performance, but when averaging almost 27 MPG, I will take that tradeoff.

Figure, once my cat is gone, I hope to hit closer to 30 MPG.

Just an FYI, for those that are struggling to troubleshoot their stalling problems.

 

This is not true, the oil pressure switch is a redundant device, in other words, a fail safe, for when the fuel pump relay goes bad.

In your case either the ECM driver for the fuel pump relay or the fuel pump relay itself is bad.

RBob.

 

You're also wrong about the knock sensor... There ARE only 2 parts to the ESC system on the 3.1 (2.8 doesn't have it)... The sensor, and the ECM and MEMCAL, which contains the knock decoder board. The ignition module has NOTHING to do with the knock sensor system.

The purpose of the oil pressure switch is to cut the fuel supply in the event the engine stalls (front end crash pushing the radiator into the engine or rear crash locking the rear wheels) to prevent fuel from spraying all over the place and preventing fires (in the case of a crash).

 

I don't understand your response to my post. You use the 'sign guy' to agree with what I posted. Then post that the oil pressure switch is used to cut the fuel pump the event of an engine stall.

It isn't used to cut off the fuel pump. The oil pressure switch is in PARALLEL with the fuel pump relay. As such EITHER ONE by itself will run the fuel pump.

When the fuel pump relay won't turn on the pump, excessive cranking until the oil pressure increase will then turn on the fuel pump. If you are driving down the road and the fuel pump relay fails, the oil pressure switch will continue to provide power to the pump.

Try this: do a key-on, engine-off and verify that the fuel pump runs and provides pressure for about 2 seconds (then stops). Do a key-off. Now unplug the oil-pressure switch connector. Now do a key-on again and start the engine. When it runs that proves that the oil pressure switch doesn't cut off the fuel pump in the event of an engine stall.

RBob.

 

OK, the Code 43 does actually deal with the ignition module. I should have been more clear. I was getting a code 43, on cold startups. It would come on for a few seconds, and go off. Since my ignition module is less than a year old, and I have seen how the vehicle acts with that going bad already, it was process of elimination.


I'm not sure what the MEMCAL is, but I'll bet it is internally located, in the ECM. Alot of the trouble codes can also show up, if the ECM is defective. Most cars will not run, with a defective ECM. Some will run, with a defective ECM.

 

As far as the oil pressure sensor, running parallel to the fuel pump, I am not 100%?

If you are correct, then a person should be able to unplug that sensor, when it goes bad. However, I have been learned 2 things, from unplugging my sensors, that when the sending units or sensors are unplugged. One, the ECM is programmed to run the vehicle, without the signal.(i.e. the "safe" mode). Two, any sending unit unplugged, including your fuel tank sending unit, will send the gauge to its maximum reading or higher. Ever notice your temperature gauge, when cranking the engine over? If it is functioning correctly, then it should travel well over the 260 mark.

Not all V6s had that oil pressure sensor, and when interchanging an engine with that sensor to a thirdgen that did not have it, it can be left unplugged. The reverse is also true. you can swap a 3.1L without that sensor, into one that originally had it.

Every sensor, or sending unit mentioned here, operate on resistance and voltage signal. Higher resistance = less voltage, and lower resistance = more voltage. the voltage signal is either picked up by the ECM or displayed on the dash gauge. Having a faulty reading is very different that no input to or from the circuit at all. Just like a light switch, when you unplug the sensor, it is like turning the switch off. the voltage signal will be in the wires, but with nothing to connect the circuit, it stops dead in its tracks.

 

Um, yeah, code 43 has NOTHING to do with the ignition module. It's for the ESC system, which, as I said before, contains 3 parts, the knock sensor, the ECM, and the MEMCAL inside the ECM (PROM, CALPAK, and knock module combined into one unit in the V6), and the dark blue wire between. Code 42 is EST failure, which DOES have to do with the ignition module. The ECM uses the data from the ESC circuit to determine when to send the EST signal to fire the ignition coil via the module. The paths don't cross unless there is a wiring problem.

As for the oil pressure unit, it does NOT send any sort of signal to the ECM. The ECM will try to run the engine regardless if there is oil pressure or not. It doesn't care if the engine will grenade due to no/low oil flow. The OPS is a backup fuel pump switch and gauge sender ONLY.

As for the other gauge sending units... Try unplugging them on a Ford or other car. The needle WILL NOT move from its park "low" position. GM gauges are the ONLY gauges that read high when unplugged. It's been that way since the 70s and earlier.

 

Will the water pump make a bad noise before going out? My Son said the noise sounds like the water pump. He can fill vibration at the crank spinning thing.
If I drive it will it make things worse before getting it fixed? Thank for your help

 

No, the water pump doesn't always make noise before it goes to the crapper. If yours is making noise, plan on replacing it within the next 30-60 days. When the 3.1 was dropped into my car, apparently the pump had sat dry for a while. It started making noise, and then a few weeks later, I'm going down the road and steam started coming out from under the hood. I popped the hood and the pump pulley was wobbling all over the place (bearings shot) and coolant was coming out of the weep hole (bad seals). The pump WILL get worse as you drive it. It costs approximately $20-25 to replace and a couple hours if you haven't done it before (you need to remove the A/C compressor if equipped, the power steering pump, and the hose from the heater core pipe after draining the radiator, leave the hoses and lines attached to the compressor and P/S pump).

However, the water pump and a bad power steering pump make almost the same noise. Make sure of which one is going south before buying either, as there is a significant price difference between the water pump (20-25 as said before) and the power steering pump (about $70 the last time I replaced it, not counting renting the pulley remover).

 

Maverick, I thought it might be the power steering pump too, but i don't have any problems with steering. It started out as a small noise then over a few weeks has gotten worse. Is there anyway to tell the difference? Wow my 2.8 motor doesn't look like all those parts would have to come off. At least there is a lot of work space under the hood! Thanks for any info Maverick

 

The power steering may be fine now, but if the pump goes bad, it won't be. Use a screwdriver or length of hose to determine which has the bad bearing/bushing, put it on the housing behind the pulley and then to your ear.

Problem with the 2.8/3.1 is that the A/C compressor is actually bolted to the power steering pump bracket in the lower hole. The PS pump bracket's upper bolt location is dependent on whether the car is also equipped with A/C or not (and the rear bracket is different between A/C and non-A/C cars to make up for the difference). The PS pump bracket is also bolted to a boss on the water pump (the small 10mm bolt on the left side looking at the pulley end of the engine), so the A/C compressor bracket has to come off first to get the PS bracket off to get the water pump off.

 

Something else, to note on the water pumps. The 4, 13mm bolts, that are located at the 2,4,8, and 10 o'clock positions, go through the timing cover. When you remove these bolts, you must bolt a piece of bar stock, to the timing cover, after the pump is removed, to prevent the timing cover seal from breaking. I did not do that, when i replaced my pump, and i could see all the water marks, from the leak, down my block. I eventually had the entire gasket replaced, but the leak can mix oil with the coolant, if the seal breaks internally.

 

I have another update, concerning the exhaust manifold bolts that snap. I checked with a few parts stores. NAPA can get a kit, for reapiring each side. You have to purchase the sides, seperately. They come with only 2 studs, for replacing the problem bolts.

The repair shop mechanic, that i talked to, was familiar with the problem. He sent me to a machine shop. He wouldn't even touch the car. The machinist informed me, aside from the bolts breaking, that they tend to seize, inside the cylinder head. 99.9% of the time, they require the head to be pulled and the broken bolt drilled out.

As far as GM dealers? Well, they use 3 different part #'s, for the stock bolts and studs. One of the 3 types is discontinued. So a dealer will only be able to supply 2 types of bolts, if you are just installing a gasket and the stock manifold.

Are there other ways, to remove these studs, safely? If anyone has advice, I'm open to it.

For those that need to review my original post, the #5 cylinder and the #2 cylinder have a problem, with the manifold bolts snapping or threading themselves out of the head and the manifold. The stock setup is "gasketless". When the bolts break, the exhaust leaks, and carbons up the gasket surfaces. So to repair them, a gasket is usually installed.

Heck, it may be best to have decent headers installed, for the time and money you have to put into this.

 

I had this issue and just had a friend drill them out and retap them(this is for headers though) Ive never had another issue with them. Believe my I've put mine though many heat cycles to test them.

 

if mine is ever out, I plan to weld the exhaust manifolds to the block, no more leaks for good, and yes im searious.

 

What I did when I had to drill out the broken studs (in the #5 cylinder, of all places ) in my 3100 head was...

1. Remove cylinder head. There is no room for a drill.
2. Try to remove broken bolt (if the head has snapped off and left a good portion of the shank) with locking pliers or other apparatus.
3. Failing that or if bolt is broken either very close to or inside cylinder head (in which case, you're NEVER going to get it out with locking pliers!), reinstall manifold (if able).
4. Use a SHARP 5/16" drill bit. And some sort of oil (engine oil or whatever you have but NOT WD-40). Drill down through manifold as a guide to drill out broken bolt straight.
5. If you haven't already, go out and get an M8x1.25 rethread kit (heli-coil or Slimsert, etc). Tap hole with tap from rethread kit and install insert using tool.
6. Use anti-seize when installing replacement bolts/studs/etc.