94 Pontiac TransSport... power loss, poor mileage - update

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BF

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I just posted a Q on alt.autos.gm but does anyone know of a good forum for getting help on automotive mechanical issues?<br /><br />Thx<br /><br />In case you're interested here is my issue:<br /><br />================================================<br /><br />Hiya,<br /><br />I'm getting frustrated... Here's the scoop. 94 Transsport 3.1L ... Throttle body fuel injection. 256 Kkm. Drives well... I had a rough idle/loss of power. I figured a dropped a cylinder, and did plugs, wires and rotor (they were due again anyway). Now runs smooth but feels weak (down on power) and getting poor mileage. I put a new O2 sensor in (no change) and checked compression (all good)... plugs all look the same, and disconnecting any plug wire affects the idle (so it's firing on all). Vacuum is good.<br /><br />I figure it's burning about 1/3 more fuel than it used to.<br /><br />The CEL works, but other than at startup, it has never lit.<br /><br />So, any idea's why it might be running so rich?? Other troubleshooting ideas??<br /><br />Many thanks!!
 
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bandit86

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Re: 94 Pontiac TransSport... power loss, poor mileage - update

bad throttle body injector, hook up a pressure gauge to your fuel line and see if fuel pressure drops off as soon as you turn the engine off. You could also have a dead squirrel or other rodent in your intake, blocking up the airway
 
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BF

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Re: 94 Pontiac TransSport... power loss, poor mileage - update

I like the fuel injector thought... LOL on the squirrel. Nope, intake is not blocked.<br /><br />I take it fuel pressure should hold after shut down? Is there usually a port on the fuel line somewhere to hook a guage to?<br /><br />I had also thought that maybe there was a separate temp sensor for controlling the mixture... If it's gone, maybe it's staying in "cold weather" ultra-rich mode. BTW, the temp gauge works fine, so it'd have to be a separate sensor if this was the problem.<br /><br />thanks for the input
 
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bandit86

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Re: 94 Pontiac TransSport... power loss, poor mileage - update

yes there is, like a tire air fitting somewhere on the fuel rail<br />youre right about the temp gauge, you have two sensors, one for the gauge and one to tell the computer what to do. also have an intake air temp sensor, but yes, could be in choke mode.
 
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Copespitter

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Re: 94 Pontiac TransSport... power loss, poor mileage - update

Check the EGR valve.<br />My Suburban was running rich and had a lack of power and that was the culprit.<br /><br />There's no reason to search for another forum. There's some very knowledgable people on here. <br />I'm sure someone will figure out the problem.
 
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BF

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Re: 94 Pontiac TransSport... power loss, poor mileage - update

Thanks for the responses.... Some new info:<br /><br />I found out how to read the codes... (with a good ole paperclip) even though there is no CEL, I get a code 34, which is a MAP sensor low voltage error...<br /><br />I found some MAP sensor info too... in the few min's I had to check into it, it seems like the sensor functions OK without the engine running (puts out ~4.5 V)... I haven't yet checked to see whether it drops when I start the engine. <br /><br />To me, running rich doesn't seem to fit with a code 34 (too low of MAP voltage) (?) Low voltage would make it run lean if I understand it right ?<br /><br />So I'm not sure if the error code is showing the problem, or whether it might be a stored error from when I had it running without the air cleaner on it over the weekend, looking for a vacuum leak. (That is it was idled with the MAP disconnected)<br /><br />Anyone know how long the codes are stored for? Is it a certain number of starts? Or is there a DIY way to clear them? Grounding the positive battery terminal work? It'd be nice to clear the code and see if it comes back. I'm not keen to drop $90 for new MAP sensor unless I'm pretty sure it's the culprit...<br /><br />I didn't have a chance to look at the injector yet...<br /><br />anyway, that's the update so far... How does one check the EGR valve?<br /><br />Thanks!
 
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BF

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Re: 94 Pontiac TransSport... power loss, poor mileage - update

I renamed the thread... hopefully didn't loose y'all!
 
Bob_VT

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Re: 94 Pontiac TransSport... power loss, poor mileage - update

How is the Cay converter? If it is clogged you will have reduced power. Just a thought.
 
dolluper

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Re: 94 Pontiac TransSport... power loss, poor mileage - update

Clear your codes by disconnecting your positive battery cable for a minute,but you will loose clock setting and programed radio stations.BoB's idea at looking at a restricted exhaust system is a good choice,for lose of power and bad gas mileage as would be the EGR valve,to check your EGR ,start it up place your finger up under the top cone and raise your RPM above 1500 ,you should feel movement of the diafram,if not use a vaccum pump and see if it holds pressure there is a bleed off on the top that must be covered,no luck on that test get a new gasket and pull it off and check intake cavity for carbon build up and also take a soft headed hammer and knock on EGR to release carbon from inside.Plus clean your Throttle body could also be carboned up .That should keep you busy for awhile :D :D
 
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BF

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Re: 94 Pontiac TransSport... power loss, poor mileage - update

thanks for the info... <br /><br />Another update... this morning I noticed something else. I seem to be burning coolant. I knew I was loosing some somewhere, but on a cold start it puts out a fair amount of moist, white exhaust.... (and it's warm out this morning) not noticeable once the exhaust sytstem heats up. Hmmmm... wouldn't I see a bad head gasket on the compression test? Maybe not always?<br /><br />It runs surprisingly smooth if it's got something major going on! Any thoughts on this? Or is there some other way coolant could get in the cylinder?<br /><br />Oil looks good, no coolant in there. Funny that a plug didn't look steam cleaned (?).<br /><br />The plot is thickening!<br /><br />Thanks!
 
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bandit86

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Re: 94 Pontiac TransSport... power loss, poor mileage - update

wouldn't notice slight antifreeze consumption. I had a car with a cracke dhead that went through more antifreze than gas, actually drove better
 
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TilliamWe

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Re: 94 Pontiac TransSport... power loss, poor mileage - update

I saw this post yesterday, and said to myself, "the main reason 3.1s lose power and drop fuel economy is when the intake manifold gasket goes bad ,and anitfreeze leaks into the engine". Ta Dah, I am a genius! <br />Well, not really, but apparently, this is a common problem with the GM engines (including the 3.8, which is not related to the 3.1 at all). It's even worse if you have Dexcool! Check all your connections at the intake manifold (heater especially), but don't be surprised if you end up having to remove the whole manifold. Best of luck
 
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BF

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Re: 94 Pontiac TransSport... power loss, poor mileage - update

so, OK Tilliam... what lottery numbers should I buy?? :) <br /><br />So, how does the intake manifold gasket relate to coolant leaking in? (assuming I'm not spraying antifreeze on the outside of the manifold) Does a coolant line attach to the intake itself, and then go through a passage in the intake to get to the block (?) and when gasket goes south, there's a direct passage into the intake (?again?)...<br /><br />I'll have to look through the service manual tonight to see some picts. Thanks for the idea.... I'd assumed burning coolant would mean bad head gasket.
 
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Xcusme

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Re: 94 Pontiac TransSport... power loss, poor mileage - update

Originally posted by BF:<br /> so, Does a coolant line attach to the intake itself, and then go through a passage in the intake to get to the block (?) and when gasket goes south, there's a direct passage into the intake (?again?)...<br />
Click to expand...
Yup, there's passages thru the intake manifold for coolant. When the gasket lets go, coolant can go into cylinder and/or oil system. GM has an improved gasket kit to include new intake bolts with threadlocker etc. Currently, class action lawsuits are pending concerning this gasket issue. I currently have a 3.1 Chevy motor and I'm watching my coolant and oil fluids closely for this exact reason.....way to go GM, design a turd and don't stand behind it. Small wonder GM is in big trouble. This is the last GM vehicle I'll ever own,...seems I'm not alone.
 
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Elmer Fudge

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Re: 94 Pontiac TransSport... power loss, poor mileage - update

That happened recently to my toyota camry, it culprit was a bad battery connection.
 
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TilliamWe

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Re: 94 Pontiac TransSport... power loss, poor mileage - update

so, OK Tilliam... what lottery numbers should I buy??
Click to expand...
4 8 15 16 23 42 Of course! :D <br /><br />X, I'll believe you about the suit. I thought it was about Dexcool. Or is there a second one for the Dexcool problems? :mad: :confused: <br /><br />BF, yeah, my friend had a Olds Silhoutte of near the same vintage and had the same problem. It cost his about $900 for a shop to do the work. But if you are mechanically inclined, you could do it yourself. Best of luck!
 
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Xcusme

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Re: 94 Pontiac TransSport... power loss, poor mileage - update

The class action was for the gaskets Link...<br /><br />Here too Link..<br /><br />The gaskets and Dexcool are both problems....too many websites to list.... :eek:
 
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BF

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Re: 94 Pontiac TransSport... power loss, poor mileage - update

thanks for the additional info<br /><br />maybe this is the culprit... seems like a strong possibility. Even if there's something else going on, pulling the intake in search of the coolant burning thing might not be a bad idea.<br /><br />Probably won't have time to dig into it for a couple weeks.... but when I do, I'll revive the thread and give an update.<br /><br />funny I hadn't heard about it before... I usually take notice of things like that.... <br /><br />I'm kinda partial to these vans, I have 2 of 'em... both 94's the other has the 3.8, lower km's and is going strong. Eventually I'll know every nut and bolt on them. This is the first time a problem hasn't been easy to diagnose and fix.<br /><br />thanks again
 
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TilliamWe

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Re: 94 Pontiac TransSport... power loss, poor mileage - update

Not trying to jinx you, but the 3.8s do it too. Or at least something intake manifold related. Almost every wrecked Buick Park Ave with over 162000km that I have inspected, the owners have told me that they just had the "intake manifold work done".
 
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