92 Lumina 3.4 dohc running rich, surges, stalls

[OldMike]

Hoping someone on here can help. I've got a 1992 Chev Lumina with the 3.4 DOHC and automatic trans. The cars got about 99,750 miles on it. The engine runs extremely rich at all speeds- floor the pedal on the open road and the car behind is enveloped in sooty black smoke. Gas mileage is just awful- less than 10 mpg. The worst part is low speed driving- in traffic, the engine "loads up" and starts surging and bucking and trying to stall. And it WILL stall unless a left-foot-brake, right-foot-on-the-gas tactic is used. At highway speeds it runs better but still blows massive amounts of unburned fuel out the twin tail-pipes. The check engine (actually it says "service engine soon") light is on sometimes but not always. There's a "low coolant level" light which has been on constantly since we got the car but it was on for years before this problem showed up. We'd had previous trouble with the car, and had the the lower intake gaskets, timing belt and ignition module replaced at about the 65,000 mile mark. The car ran "okay" after that but the repair bill was enough for a down payment on a new Bentley! Now we've got this new problem and just can't afford another four-figure trip to the repair shop.

 

I've checked all the vacuum hoses and can find no leaks. Also pulled and cleaned the IAC valve and it appears to be okay. Not really sure what else to try- I'm an old school points-and-condenser guy and don't have any of the fancy scanners and code readers for newer cars. Hoping maybe it's something simple that I've overlooked? One odd item- the speedometer on this car doesn't have a cable, it's electronic, and it sometimes "sticks" at about 41 mph even when the car is stopped. But it was doing that when the engine was running okay so not sure if this could relate or not.

 

One possible clue- sometimes the car is idling, surging and getting ready to stall. Suddenly, the check engine light comes on and at the same time the engine speeds up, smooths out and otherwise runs almost normally for a minute or two. It doesn't always run normally when the light is on, though. Usually when the light is on it runs awful as described above.

 

I've been trying to sell this car since the summer (had an ad on this forum as well as about 7 others) but with the current engine problems nobody will touch it- this engine's got a rep for being high maintenance and even at giveaway prices nobody wants to get involved with a "money pit". If I'm going to be stuck with the car I'd at least like to get it running, maybe I can use it as a winter driver and keep my ancient Buick away from the NYC salt this season. My apologies for the long post but I'm trying to give as much detail as possible and not leave anything out. Hopefully, somebody's had this problem before and will recognize it.

 

Much thanks,

 

-Mike

[AL]

ICM, its underneath the coil packs

[RobertISaar]

honestly...... there could be so many problems that are combining into a single monster issue.... you really need to see what the PCM is reporting. there is the possibility of a failed/failing PCM as well.

 

ICM(and coils) would be a good start, i would also look into checking/replacing O2, TPS, MAP at a minimum.

 

if it has been running like this for any amount of time, expect to need new spark plugs as well. and at that point, if the wires are even questionable, replace them.

 

when the speedo sticks, does the odometer keep rolling at the rate of ~41MPH?

[OldMike]

My thanks for the responses. Couple of questions- How do I see what the PCM is reporting? How do I test the ICM, coils and/or PCM without laying out long $$$ for new parts? There aren't any good junk yards around here these days. Is these a surefire way to diagnose this problem by eliminating suspect parts one by one, preferably without replacing them?

 

I'd like to hook up my vacuum gauge to see what kind of vac the motor is pulling, but there's so many connections I'm not sure which one to use. Any suggestions?

 

I'd like to try to get this car running so it is usable and/or saleable, but I don't want to dump more $$$ than it's worth into it in the process. I've got a volt meter, vacuum gauge, a dwell tach and a timing light, that's about as sophisticated as it gets, tool wise. I'm an old school mechanic though....once I know what's wrong I can fix it. Just a matter of figuring out what to replace, instead of buying and installing stuff one-by-one. Any suggestions and/or advice much appreciated.

 

Regards, Mike

[RobertISaar]

you'll need an ALDL cable or a good scanner to see sensor data. coils can have their primary and secondary resistances checked as a preliminary measure. those numbers can spec out good, but still be faulty, but if they're out of range, they won't work right at all.

 

testing the ICM is a bit more complex. i seem to remember these as being accurate:

 

http://easyautodiagnostics.com/ignition_gm/ign_module_test_1.php

http://easyautodiagnostics.com/gm_coil_pack/gm_coil_packs_1.php

 

PCM... is pretty much a "replace if nothing else seems to be the problem" resort.

 

nearly any vacuum connection should work, just don't disconnect the fuel pressure regulator vacuum line, that will potentially cause even more problems.

[OldMike]

Much thanks for the reply and the links. Will try to get out there this weekend and see if I can figure this thing out.

 

ALDL cable- do I hook this up to a laptop? Or some sort of hand held scan tool? Is my cars "diagnostic connector" the little harmonica-looking gadget just forward of the drivers right knee? I'm told that if I jump connectors A and B I can read codes by counting flashes of the Service Engine Soon light, is this true? And which connectors are A and B?

 

I'd not looked under the dash before in this car and saw a little yellow button. Thunk- its the trunk release. And to think all this time and we never knew it was there.

 

I realize I forgot to answer the question about the speedometer- the odometer seems to work fine, but the speedo sometimes reads 41 mph even when going slow or stopped. Not really sure how/if this relates.

 

Thanks again!

 

-Mike

[RobertISaar]

ALDL cable hooks between the port you described and a laptop.

 

pins A and B are correct, refer to this pic for easy reference.

 

 

so, the rightmost pins of the top row will be the two you connect together. don't be surprised when you see that this pic shows a lot of pins in different spots than what you have. that is a platform/options dependant occurance. there are guides out there on how to read the SES flashes, i seem to remember one being in the FAQ section of the site too?

 

speedometer sticking, but the odometer still rolling at the correct rate would imply that the speedometer itself is the issue. the PCM gives the instrument cluster a 4,000 pulse per mile signal, which almost directly drives the odometer, but goes through a few conversions steps for the speedometer. sounds like the problem lies there.

[OldMike]

Much thanks for the response. Didn't get a chance to work on the car last weekend, had to put in a little OT. Hoping to get a look at it tomorrow.

 

Question- would jumping the two terminals and counting the flashes give the same information as an adl cable and a laptop? I've got a laptop but the cable costs a few $$$ and really not in the budget this week. How do I interpret the flashes? Most of the codes have zeros in them how does that translate to flashing lights?

 

Someone told me I should pull and clean the EGR valve, could this help? It's an odd looking piece like three silos close together. How does one get the connector off? It's not self explanitory and I really don't want to force it. If I can't get the Two Ton titanic running right before winter I might have to sell it to the demolition derby maybe that would be best

 

Much thanks again for the help.

 

-Mike

[tornado_735]

For the love of God, don't sell it to someone who is going to demo it.

 

There are very, very few Lumina Euro 3.4s left.

 

If I had the scratch, I'd gladly make a trip to Yonkers to pick it up.

[GP1138]

http://www.gmtuners.com/OBD1_DTC.htm

 

And I'd lay money that this is an ICM/Coils issue. Go to a junkyard and get yourself a whole set, should set you back $40 at the most.

[RobertISaar]

you won't find any 0s in codes that get flashed over the SES bulb. GM specifically avoided that situation, along with avoiding higher numbers in general.

 

an ALDL cable will show so much more than just codes.

[Crazy K]

The paperclip trick is not as foolproof as using a scanner/laptop, but can be helpful if it still has a useful code stored.

here's some how to:

http://www.w-body.com/showthread.php/14922-How-to-pull-codes-%28OBD-I%29

http://www.gmwbody.com/forum/faq/gm-obd-1-trouble-code-information/?wap2

 

Whatever is wrong, I suspect it to be a sensor; the car runs better when the check engine light is on because the PCM stops using data from that sensor, deferring to an alternate operating procedure. A module such as the ICM does not have such a back up. ***but more than one part could be bad or weak

 

You could have a bad oxygen sensor, for instance, that thinks the car is running leaner than it is and enriching the mixture erroneously. When the PCM realizes the data is out of range it starts operating on a different set of instruction to determine fuel mixture without using the oxygen sensor. Presto, the check engine light is turned on and the car runs smoother, but with a decrease in gas mileage of maybe 30% as the PCM failsafes to be a bit richer than it would be in proper running condition.

 

If you do need a coil/ICM, you can get the parts from most any GM 60degreeV6, the ones on top of a 3100/3400sfi engine are the same but not exposed to intense exhaust heat like on 3.1mpfi/3.4dohc cars. the mounting plate is different, but eh module and coils are the same.

 

lets see if the ICM is functioning well, do a spark test:

take an extra plug wire (if possible, or you will have to unhook the plug wire end of each wire) and shove a screwdriver into it. Lay that on top of the engine and swap the other end for each coil end. crank the engine and see if each of the six coil points sends a spark though. Look for equally rich sparks from each coil. I want to say they should all be blue... orange being a sign of weakness...

[RobertISaar]

a thin, orange spark is bad, a fat, blue one is ideal.

[OldMike]

• Titanic update- got my trusty paper clip out and jumped the two terminals as instructed. Sure enough the light started flashing right away. First was 12 like its supposed to be. Then came 23, then 33. That was it. 33 was low vacuum to one of the sensors and I'd already looked at all the vaccum lines. But 23 was manifold/air intake temp sensor reading too low. So I started looking 'round the vicinity of the airbox since the airbox is pretty pranged on this car and it was a good place to start. There's a connector there, a blue one, which didn't look quite right and another loose connector, also a blue one, which was just hanging out there not connected to anything....most likely the connector to the washer pump/tank whch hasn't been installed in the car for a couple years now since it needs to be jump started at least three times each winter. To make a long story short, it looks like the guys who installed our new battery a while back rammed the washer pump connector into the airbox connector or at least tried to. Cause the two were the same color I guess? Got that hooked up correctly and started her up. And would you believe, she ran better? Not perfect, still surging when you first start her up, and still with the check engine light on, but a whole lot better than what we had before. But the problem does come and go, and it may have just been a "good day" for the engine. Didn't have time to do a full road test but will try that tomorrow and hope for the best!
  
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Much thanks to one and all for the advice and guidence. I'm not sure she's out of the woods yet but at least we're making progress! Will continue the sage tomorrow I guess.

 

Thanks again!

 

-Mike

[OldMike]

Finally got to take a better test drive today. Not perfect, but a whole lot better than last week. Still stalling when cold but nothing like before. Who's have thought such an intractible problem could be fixed with a paper clip? Plus about a million dollars worth of free advice from those on this forum. Much thanks to one and all!

 

Car is still for sale BTW. If this whole experience proves anything it's that a car like this needs to be in the hands of someone who can work with it's...shall we say...peculiarities? I'm gonna stick with my '68 Buick, yeah it eats gas but at least I can fix what needs fixing!

 

Thanks again for the help,

 

-Mike