Bad fuel mileage, occasional rough idle

[safari kev]

My 94 has been giving me fits the past couple months. It gets bad mileage (13 city and below), idles rough with gas smell from exhaust, and likes to stall when putting it in gear when cold. It will very very rarely do it when warm, but when cold (especially when cold outside) it will idle rough and stall when it goes in gear. It will also have a dead spot just off idle ONLY for a couple minutes when cold. I have replaced vacuum lines, EGR, IAC, cleaned the MAF sensor, and put in Delco cap and rotor along with 4 of the 6 wires (working 50 hours a week doesn't leave much time for working on the van). What has me so stumped is it only does it when cold and after a few minutes the dead spot off idle is gone and it runs fine. Also, when cold, if kick the fan on high and turn on the A.C., it will immediately stall.

[AstroWill]

I would probably check the computer, see what the temperature sensor is reading at.

[Astrophysics]

Also, with car warmed up after driving 10 or more miles stop and leave motor running.and motor running in Park with parking brake on, to check if it running rich due to leaking plastic fpuel injection lines or poopets, , might borrow an infra red tempuratue gun. "Shoot the input flange on the catylitic converter and write down the temperature. Then "shoot the output flange of Cat and write down that temperature in degrees fahrenheit.
A proper functioning Cat. With fuel mixture correct shoild only be about 100 to 150 degrees hotter at outpt of cat as it burns the extra hydro carbons. If the delta temp is super high, for example 200 to 300 degrees, it is running super rich. And fuel injector lines could be leaking under the manifold and puddling up excessive fuel.
AP

[safari kev]

Temp sensor was replaced (threw a code). It really ran bad.when that went out.

I'm almost.thinking the IAC is bad. It ran.great for about a week after I replaced it. Then it started acting up again. It's a standard motor.products part. (All that carquest had in stock at the time)
I'll have to check the exhaust temps and get back to you on that. I work 50 hours a week, so not much time to work on the van.

[safari kev]

So tonight I drove it around, and the roughness persisted while driving. First noticed it while getting on the highway. Did a WOT pull up the ramp and it felt down on power....like it was stuttering. Hit 65 and it bucked a bit and really didn't seem to want to go any faster. It seemed to bedown on power a bit too. Did 60-70 for a few miles and got off. It shuddered constantly at idle. Not really a miss, but the exhaust was pulsating in a pattern and it wasn't idling smooth. Got to where I was going for dinner, and it acted like it wanted to stall when backing up slowly.
Got it home, and it was still shaking a bit at idle. Revved it up and the exhaust rattled and the engine bucked. The exhaust was also rich smelling. I'm guessing obstruction in.the cat or fuel delivery issues

[sandfly]

fuel regulator leaking and or bad

[Astrophysics]

Better fix the rich fuel situation or you could have a real bad thing happen like happened in my 1994 V6 4.3 liter S10 Chevy Blazer....
The fuel injector spyder hoses leaked so much raw fuel into the exhaust that it finally blow a hole in the muffler.

Fix it if you can. The spyder kit is not too expensive but you do have to remove the intake manifold to get to spyder.
good luck

AP

[safari kev]

Well, took it to my mechanic. my cat is clogged for starters. So I'm getting that done next week (in the meantime, van is parked). Putting a full walker system on it and new 02 sensor (bought it off rock auto....cost me 410 shipped). Mechanics charging me 80 for installation (So total is only 50 bucks more than a generic exhaust system with generic cat from an exhaust shop). I guess I finally have to bite the bullet on new exhaust (mufflers been shot since I bought it nd it has developed holes in the pipe before the muffler) After I get that done, I'm gonna have them check the fuel system. (Mechanic thinks the injector or spider is going out).

[Astrophysics]

DANGER. STOP. !!!!!!!!!!!!


Fix the fuel injector spyder first!!!!!!!


I made the same mistake you are about to make !

The new Catylitic converter Cat, will get so hot trying to burn off the raw gas, that it will cause the back fire at freeway speeds and the explosion will literallt blow a hole in your shinny new muffler!

That is exactly what happened to my 94 S10 Blazer!


Repeat, fix by replacing spider in fuel injection first!

The mechanic should know that. He could do a fuel pressure leak down test to verify the leaking spider.but you can simply know that he will need to pull intake manifold and install new spider kit.
Do a Google search for fuel injector spyder and see, better yer type You Tube 1994 chevy fuel inj. Spyder

AP

[safari kev]

The mechanic already told me the injector or spider is bad (or possibly the coil, but he said he's 95 percent sure before testing it that the injector/ spider is bad). Basically, it's getting a new exhaust (since it needs one anyways), then he's gonna start testing the fuel system. It's not leaving the shop until it's fixed.

The weird thing is when I drove it home the other night, it drove great. Tons of power and no weird idling or feeling sluggish. No gas smell either. Parked it on the street to pull out my car (since I'm not driving it until it's fixed) and restarted maybe 30 seconds later and it and it ran like crap and smelled like gas out the tailpipe.



Oddly enough, my 95 astro had a bad FPR (which is part of the spider assy). It would spit gas out the tailpipe and fouled the number 4 plug in a week. Had all the same symptoms but added spitting raw gas out the tailpipe and low speed stalling. Of course, it got totalled 2 days before it was supposed to go in for a new spider/ injector so I lucked out on that repair.

[Astrophysics]

Hi Again,

Since it is a 1994 it has the simple OBD I, On board diagnostic, 1 st Generation. The yellow dash light can be used to read the codes.
Your mechanic can plug in the OBD I could reader which basically caused the single dash light to flash out a simple series of flashes, kinda like MOrse Code.
Sounds like you could have a bad MAF, Mass Air Flow Sensor, this would cause a code 34, flash, flash, flash; pause flash, flash, flash, flash.
and repeat series two more times.

If there are no faults the dash light will flash code 12. Which is Flash; pause, Flash, flash. and repeat the series two more times.

Good luck

AP

[safari kev]

Van throws no codes ( all I get is 12) and I've tried unplugging MAF and it ran pretty much the same.

[Gorwoc]

For my two cents I think you're on it. My 95 did the same thing at the same mileage. It doesn't like low fuel pressure and if it won't hold pressure it acts like that. Mine did and after ruling out the pump and finding low pressure (45psi) and leak down, I centered on the the regulator. You can replace the regulator alone by drilling out the tamper-proof screws but it's not worth it. My spiders tubes were hard and the poppet clips broke pulling them out. I think anybody should replace the whole system, regulator, injector, and spider and start fresh. And I think it's great if you do the exhaust now as well. After my experience with the fuel injection I think it put so much extra gas down the system that it's messed up my converter. Good luck with it.