1994 Chevy Surburban running way too rich and ...

[T-Max]

My problem sounds a lot like Cside's problem with his 1992 Suburban.

The problem started yesterday on starting. The truck ran fine last time I drove it so it was surprising when I started it yesterday afternoon and it was missing badly. It kinda cleared up a little and I drove it a couple of miles to where I get onto the highway at a stop sign where traffic is heavy and flying and it's tough to enter most of the time. When I got my chance I goosed it and it almost stalled completly. I had to ride the shoulder and nurse it up to speed before entering the slow lane.

It's still that way. It starts hard and clearly runs way too rich with black smoke. It clears after a few minutes but is still idling too fast. And I can only get it going without stalling by letting up on the brake and letting it get itself rolling at idle, then gently nursing the gas pedal to get it up to speed.

At highway speed and rpms at or above 1500, I can goose it and it goes just fine.

This has electronic fuel injection and I looked in the carb at idle and it looks to me like it's dumping too much gas in there at idle, but what do I know.

There are no error lights lit and I know of no way to "adjust" the carb.

This is a high mileage vehicle (200K miles) and I doubt if the fuel filter has ever been changed. But it's getting TOO MUCH gas, so I don't think that's the problem.

I haven't searched the forums for a possible answer, but if anybody has any ideas what might be causing the problem, I'd appreciate any and all suggestions. I believe there is some sort of control on the tranny that controls accelleration and I'm wondering if that gizmo might be the problem?

Thanks much for your help.

 

[zora]

If you have EFI there is no carburetor only a throttle body. Did you check your fuel pressure? Did you check the fuel pressure regulator vacuum line for signs of gasoline, if so the regulator is shot. Do you have a check engine light on?

 

[T-Max]

If you hVE EFI there is no carburetor only a throttle body. Did you check your fuel pressure? Did you check the fuel pressure regulator vacuum line for signS of gasoline, if so the regulator is shot. Do you have a check engine light on?

Hi Zora

Thanks much for the reply. I have not checked the fuel pressure and not sure I can do that effectively (but I'll look into it and see what it entails)

Nor have I checked the fuel pressure regulator vacuum line. But I will check that out once I identify the fuel pressure regulator and associated vacuum line. It's going to snow here tomorrw (in NJ) so I probably won't get to it until Sunday.

The check engine light is not lit.

Do you think there could be any other control or sensor that could be causing this excessivly rich fuel mixture and associated "stalling" problem? I'm a long-time shade-tree mechanic and was a professional mechanic in my youth but that was back in the day. I'm not current with all these sensors and computer controlled aspects of the modern internal combustion engine (tho' 1994 ain't all that "current") but I'm under the impression that there are at least a few sensors (or computer codes) that might be responsible for this sort of problem.

I would think that if a sensor went bad (like the oxygen sensor), the check engine light would light.

BTW, the "stalling" aspect occurs even when the engine isn't under load (isn't in gear). If you just punch the gas at idle in neutral, the engine would likely stall completely out.

It acts like a major vacuum leak problem fairly common with engines from back in the day. You punch the gas and the engine dies and sounds like it's just drawing air, rather than an air/fuel mixture. Rather than roaring to higher rpms, it just dies.

I really haven't yet begun to troubleshoot the problem. I just thought there might be someone out there who's seen it before and could peg it from the symptoms.

And yes, this engine (350) has no actual "carburetor". It's EFI and there's just the throttle body (2 throats)

The gas that's dumped into the body at idle seems excessive to me. I can see it "bubbling" up on the butterfly valves of each throat.

Is that what it should look like?

Seems excessive to me.

Then again, I seem to remember seeing that previously, and quite some time ago (long before any kind of problem like this). I can't be sure but I think I've looked in there before at idle and saw the same kind of thing. So maybe that IS normal.

But then again, my tailpipe also seems a tad too black to my eye. I'd really like to see a nice charcoal gray, not the sooty black I'm seeing.

I think the thing's been running at least a tad too rich for quite some time, tho' I haven't pulled the plugs lately. I'll be pulling at least some of those on Sunday, weather permitting.

P.S.: If anybody knows how to lean out the air/fuel mixture on one of these EFI engines, I'd love to know how.

 

[zora]

You could try disconnecting the exhaust where it attaches to the catalytic converter. If this eliminates the problem the converter is clogged. Do you have a shop manual that goes into detail on disassembling/testing the throttle body and pressure regulator ?

 

[Chuzz]

You really need to run the codes on it and see what shows up. You start shotgunning parts at it and you could spend a lot of money that you didn't need to. First things first. Read the codes and go from there. It does sound like you're getting too much gas, but it could just be a defective fuel injector O-ring or maybe the throttle body just needs a good cleaning and rebuild.

 

[T-Max]

You really need to run the codes on it and see what shows up. You start shotgunning parts at it and you could spend a lot of money that you didn't need to. First things first. Read the codes and go from there. It does sound like you're getting too much gas, but it could just be a defective fuel injector O-ring or maybe the throttle body just needs a good cleaning and rebuild.

Yes, I do need to run the codes. I believe I can get that done at Autozone (I think they have the proper gizmo for this older vehicle).

And don't worry. I don't "shotgun" problems. I'm amazed at some of the posts I read where guys have replaced just about everything that could possibly cause the problem -- and still have the problem.

I guess troubleshooting is a bit of a lost art.

If you have EFI there is no carburetor only a throttle body. Did you check your fuel pressure? Did you check the fuel pressure regulator vacuum line for signs of gasoline, if so the regulator is shot. Do you have a check engine light on?

Here's my regulator -

http://www.autopartswarehouse.com/s.../1994/Silverado/8_Cyl_5-dot-7L/AC2172900.html

If that link doesn't work, just Google "AC Delco 217-2900 Fuel Pressure Regulator" (no quotes) to see what I'm dealing with.

I don't see any vacuum line to check, so that's out. I believe this regulator is fed vacuum via a passageway (or passageway(s)) in the throttle body itself. I read one thread where a poster suggested removing the throttle body to clean the passageway. He said it can clog with carbon and that it's a fairly common problem. The issue I see there is that it looks to me like the TB doesn't "remove." I'll have to look more closely because I can't believe that's true. If there's a mounting gasket for it available (and I think there is) then it definitely comes off.

There are kits to rebuild the regulator that go for ~$35.00 or less. That's how I'd go if I decide that's the problem, or if I just want to eliminate that as a possible cause. After I get the codes read, that is.

I think this problem has been coming on for some time, so this regulator is the likely cause.

 

[Cside]

Mine is still sitting. Had a bad flu cold and have been down for the count the last 2 weeks. Let me know how yours works out. I will have mine looked at soon.

 

[T-Max]

Since my last post I've found several YouTube videos which are helpful for showing how to remove / rebuild the fuel pressure regulator. I also now know that the throttle body does indeed come off and some of the videos show that as well. I can post the links to the videos if anyone is interested.

I've also found a number of new regulators on ebay. Autozone also sells them new as do most auto parts stores. Interestingly, a new one (aftermarket brand) costs only a few dollars more than the aftermarket kits to rebuild the old one.

If you want an AC Delco one, you'll pay a lot more, as per my prior post. Aftermarket regulators are considerably less expensive and seem to be readily available.

In one of the YouTube videos I saved the guy found that the temperature sensor was the cause of his problem. His 454 was running rich and he suspected the MAP sensor as the usual suspect, with the temp sensor the next likely candidate. He said it's rarely the fuel pressure regulator but since I now know all about that and what's inside it, I find that hard to believe. My truck has nearly 200K miles on it and I'd be surprised if the diaphragm inside there wasn't shot by now.

I can't think it's my temp sensor because my temperature gauge works just fine. So at the moment, the fuel pressure regulator is my #1 suspect. Since there's really no way to test it (unless there is a vacuum hose connection for it and I find fuel in that line) I might just have to take the "shotgun" approach and replace it.

 

[Chuzz]

Have either one of you guys considered that you may have gotten some "bad gas" with water in it? Maybe a bottle of water remover would help.

 

[T-Max]

Have either one of you guys considered that you may have gotten some "bad gas" with water in it? Maybe a bottle of water remover would help.

That's a possibility, especially for me since I never fill this thing up and I could have a lot of condensation water in the tank. So a can or two of dry gas sure wouldn't hurt.

In the meantime, I worked on it a bit today. I pulled a plug out of each side and although they are clean-burning, there's a ring of carbon on the base of each plug. So it's running rich on both banks. The fact that they are clean-burning is likely due to my last trip of 15 miles (highway) and then shutting it off on arrival home, and not starting it up since.

I then fired it up and it ran like crap at idle but did smooth out a bit after a few minutes. I let it idle for 15 minutes and it was then running smooth (at idle). No misfiring. I had the air filter assembly off as well as the spacer. This was so I could see the injector spray(s) better. They appeared fine although the right side seemed maybe a tad "sporadic." But what I did notice after the 15-minute warm up was that the pressure regulator definitely seemed to be leaking a bit. It appears to be a fairly slow leak, but a definite leak. I wouldn't think it was enough to contribute to making the engine run rich, but it would seem to be an indication that the diaphragm is leaking, which means that it's likely not working properly. So I went to Autozone and got a new one (for $58.84, including the tax) and I'll put it on tomorrow.

This may not be the cause of my hesitation problem, but since the one on the truck now appears to be clearly leaking, there's no point in not replacing it.

Incidentally, the truck ran okay to the parts store and to two other stops I made on the way back. I shut the truck off at each stop and each time I restarted it, it ran badly for a minute or two. And two of those stops were just for a couple of minutes, so it looks like restarting is a problem (as opposed to just letting it idle for a few minutes). Not sure what that means, but there it is.

As to the hesitation, as long as I get it up to 1500 rpm, I can then accelerate without hesitation. But I have to nurse it up to 1500 or it bogs down very badly.

So it's driveable, as long as you don't goose it from a dead start or when moving very slowly at low rpm. If you do, it'll just die out and stall.

BTW, as to the watery gas possibility, I did recently get two separate 10-gallon batches, the last one on my last ride home, which was after this problem suddenly popped up. So I would think that the second batch would improve the problem if the problem was due to the first batch being watery. That is, unless the second batch was also watery.

Both batches were bought at the same station with 3 weeks time in between. I doubt they'd be having that much of a water problem over that time period or they wouldn't be doing much business anymore.

Plus I drove the truck quite a bit after purchasing the first batch and had no problem at all. And I was pretty low when I got that batch, so it was essentially the only gas running the truck after the purchase. If it was watery enough to cause this problem, I think I would have seen it sooner.

 

[Chuzz]

Do you have an external fuel filter? If so, I'd suggest changing it. If you're running your tank that low, it could have picked up some trash. I don't ever let any of my vehicles get under 1/4 tank. Fuel pumps need to stay submerged in gasoline in order to run cool. Constantly running low or running out of gas will cause them to fail prematurely. And since they're in the tank, replacing them is a pain in the butt nowadays. I'm about 90% sure there's an external fuel filter under the vehicle. Replacement will probably be between 10 and 15 dollars.

 

[T-Max]

Do you have an external fuel filter? If so, I'd suggest changing it. If you're running your tank that low, it could have picked up some trash. * * * And since [Fuel pumps are] in the tank, replacing them is a pain in the butt nowadays.

Yea, I do have an external fuel filter and it should be changed, if only for the reason you say. But that's not the cause of the problem I'm currently dealing with.

As to the fuel pressure regulator, I put the new one on and (as I suspected) it didn't fix the problem. The truck actually runs worse now than before, but I'll give it some time before concluding there's a problem with this new FPR, which I doubt is the case anyway.

From the smell at the tailpipe, it seems to still be running rich. So I'll move on to the next suspected cause of my problem. I forgot to mention in my last post that AutoZone can't run the codes on this '94 truck. He says they can only run codes on '96 and newer vehicles.

I may have to break down and take this to a shop to have them hook it up and see if they can figure out what's causing the problem. I might replace the temp sensor first since that's a rather inexpensive item and the one guy on YouTube swore that's often the cause of all kinds of problems, and was indeed the cause of his problem. He also had replaced his FPR with a spare one he had -- and his truck also ran worse with the replacement FPR. But once he replaced the temp sensor, he said his problem was solved.

Go figure. Like I said, mine appears to be working okay because it seems to be correctly registering coolant temp.

In any event, the old FPR was indeed leaking and needed to go.

So there's that. But I didn't think it would solve my hesitation problem, and it didn't.

 

[T-Max]

* * * I might replace the temp sensor first since that's a rather inexpensive item and the one guy on YouTube swore that's often the cause of all kinds of problems, and was indeed the cause of his problem. * * * Like I said, mine appears to be working okay because it seems to be correctly registering coolant temp.

Just found out that the coolant temperature sensor is separate from the temperature gauge sending unit. Thus the fact that my temp gauge seems to be reading correctly is irrelevant. The CTS could still be bad.

I've seen quite a few guys say that it was indeed their CTS that was bad.

One guy found that it was his oxygen sensor.

AutoZone has it for $16.99. They also have the oxygen sensor for $18.99. So I might get those and try the CTS first and see if that solves the problem. If not, then I'll do the O2 sensor. If the CTS fixes it, I might or might not take the O2 sensor back for a refund.

I guess I'm officially now in full "shotgun" mode. Seems that with these engines and all their sensors, there's really no other way without full blown testing equipment. And even then, from what I read, you might not know. Some guys say they got blown codes, which they cleared, but then later didn't get codes when the problem came back again. So the codes don't seem to be a reliable way to diagnose these problems.

Speaking of which, I should clear any codes I might have. I haven't done that yet. Not sure if just sitting overnight works to clear any codes. I might as well disconnect the battery and do it that way, I guess.

 

[Chuzz]

You can get the basic codes yourself. Lazy people at Autozone, Advance, etc. They hire these dumbasses that can't do anything without the computer telling them how. If you know where your diagnostic link is under your dash, you can use a paper clip to retrieve some basic codes. Bend the paperclip into a U-shape. Find the link under the dash and looking at the top row, insert the paper clip into the last two holes on the upper right side of the link. There will be two sets of connectors, one on top of the other on that link. Repeating myself, insert the paperclip into the top row, last two holes on the right. Turn you key to the start position and DO NOT crank the engine. Upon turning it on, your CEL light should start to flash any stored codes. Each code will flash 3 times in succession and then move to the other codes. For example, if you have a code 23, the CEL will flash two times, pause, and then flash 3 times. It will do this three times in a row, so pay close attention. Once it's done with any stored codes, you should get a code 12. One flash, pause, then two. It will also give you this code three times. Post the codes here and I'm sure someone with a book can tell you what they mean. And if you don't catch them all the first time, no big deal. It will continue to flash the codes until you turn the switch off and remove the paper clip. Don't start the truck with the paper clip still in there. It could short something out. Back years ago when I worked at Autozone, we even gave away special "keys" so customers could run their own codes. It was basically a piece of aluminum cut to resemble the shape of a key with a notch cut out of the end for the gap in the plastic between the two holes. If I were an artist, I'd draw a picture, but you seem plenty smart enough to figure out what I'm saying here. And I'm NOT an artist! Hell, I can barely draw a stick figure. Post back and let us know what, if any, codes show up. Do me a favor and don't tell the idiots at Autozone how to do this. Why share knowledge their manager and PSM should already know and be teaching the doofus' they hire?

 

[T-Max]

You can get the basic codes yourself. * * *

Thanks Chuzz. You beat me to the punch because I just came on to post about that. I found out about it and just got done watching 2 YouTube videos (just for fun) that demonstrated how it works. In the second one the guy actually had one of those free keys you mentioned (from AutoZone).

I will read the codes tomorrow and let you know what I find. I also found a couple of sites with lists of the GM codes, so I have all of the codes and what they are for.

And I NOW remember that I knew this information already. It started sounding familiar and since I always keep notes on all this stuff I'm sure I can find those notes and when I knew it before.

But of course I forgot all about it when I needed it.

Makes me wonder why I keep notes.

And I think I do have to clear the codes once I read them. Otherwise, the truck will continue to run lousy even if the problem is fixed (is my understanding). Whatever. I'll read the codes and then clear them (assuming some show up)

Thanks again for the good helpful info.

Hopefully, I'll get to the bottom of this problem eventually. It's gotta be a bad sensor since it came out of nowhere all of a sudden. That's but another reason I didn't think the pressure regulator was the problem even tho' it was leaking. I can see that it's been leaking for quite awhile and absent some massive failure of that unit, it wouldn't account for this significant problem I'm now seeing.

 

[Chuzz]

No problem, T-Max. I should have thought of it sooner, but I had two brain surgeries back in 04 and suffer from CRS nowadays. To clear the codes, just disconnect your ground cable for a couple of minutes, I think!

 

[T-Max]

* * * To clear the codes, just disconnect your ground cable for a couple of minutes, I think!

Yes, that's apparently the simple way to clear the codes (from what I read). But no need to do it since I just read the codes as per your procedure and there aren't any. Strange, but there it is. I would think that if any of my sensors were bad, I'd see a code for it. And I would also think I'd be seeing a 45 code since it's clearly running rich.

I'm about stumped at this point but I may invest in a new CTS since so many guys have found theirs to be bad. Before I do that I may disconnect the battery ground cable, just to be sure the 'puter's head is clear. And then maybe I'll pull the connector off the CTS and start it and see if I get a code for that. Might also do that with some other sensors and see what happens with the codes.

Maybe the O2 sensor is bad since it's not registering a rich condition?

I read that one guy's problem turned out to be a bad throttle body gasket. Spray some carb cleaner at the TB base when running to see if it alters the idle.

Another guy's problem was the coil wire to the distributor. Both those guys had the same kind of symptoms I've got.

What a PITA this is.

Hope all is well with you now. Thanks again for your input.

 

[T-Max]

Hold everything!

I pulled the distributor cap and saw that the spark advance thingie in there (technical term) was very rusty. Basically it's that area in the center of the distributor below the rotor with an 8-point "star" thingie in the middle, all of which is surrounded by a loosely fitting tin surround. It's about 2.5 inches wide and there are two electrical wires feeding into it at the bottom of it. I have not researched this thing at all yet, but it's gotta be the spark advance and it's clearly rusted in one position, which means (I assume) that I'm not getting any spark advance. This would explain the hesitation and the lack of any computer codes although there apparently are 2 codes related to the electronic spark circuit. But I can believe that this non-electronic (purely physical) problem wouldn't result in any codes.

I pulled the distributor already but I think I will be putting it back in and using the timing light to confirm that I'm not getting any spark advance. I'll also research this thing to see what I can find out about it, but I'm thinking this is now my #1 suspect.

As to why it's so rusted, I can only say that I don't drive this truck much at all. It sits for long periods of time and I guess the moisture of rains and sitting in one place (and without running) has resulted in this condition. I put a new cap and rotor on a few years ago (which probably have less than 5K miles on 'em) and they look in good shape -- although the freaking rotor was frozen to shaft and would not come off with the distributor in place. Which is one reason I pulled the distributor. I got it off with some WD40 and "coaxing" and found the shaft pretty rusty where it sits on it. So I cleaned that up with some fine sandpaper and corrected that problem for the time being.

Anybody knowledgable about these things, please feel free to chime in.

 

[zora]

I believe you are describing the part pictured in the center of the distributor, the pickup module.
http://www.napaonline.com/Catalog/CatalogItemDetail.aspx?R=NRD481830_0130780483

It has nothing to do with advance, that is controlled by the computer.

What codes did you get?

 

[T-Max]

I believe you are describing the part pictured in the center of the distributor, the pickup module.* * * What codes did you get?

I thought I posted back to you right after your post, but I don't see it so I'll try again.

Yes, that part (the pickup module) is what I was trying to describe. Do you know what function it has? I don't. Also, do you think the fact that mine is quite rusty means anything?

I did not get any codes. All I got was a repeating 12 code, which indicates that there are no other codes.

Update: After a little research, I now know the function of the pickup coil and (I believe) the fact that even tho' it's rusty, it doesn't necessarily affect function.