Low power, rough idle, poor MPG..???

Low power, rough idle, poor MPG..???

Postby Sailing_Faith [OP] » July 26th 2016, 5:23am

Ok, so I have been at this for a bit now.

NO Codes...

Rough idle.... (newish motor mounts, but other symptoms say something more then that)

Low power

Poor MPG (11-14mpg).

EXHAUST smells rich... Idle is really really rich smelling, but even when hot it smells like a carb with a stuck choke.

Trouble shooting So far....

Checked Engine fuel trim is pretty normal... LTFT is -3.5% on both banks, STFT is mostly normal.

Checked vacuum hoses. Actually plugged vacuum at main hose from motor and little change. (sounds like vacuum leak would cause LTFT to be high, not low).

Tried removing o2 sensor before the cat to check if Cat was clogged... no real change in power. Did not drive long enough to know if it affected MPG



Recent replacement;

Spider (new AC Delco)
MAF (ok, not replaced, but cleaned and swapped with a known good running van)
New distributor drive, Cap and rotor (skip White)
New Upstream o2 sensors
Intake Air Sensor (OBD data says 102f... seems right)

Plugs and wires were changed 20k ago, installed with new engine (yea, I know they can be bad anyway)....


What does the jury say to try next>?????

:ty: in advance for any and all help.... :bow:
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Re: Low power, rough idle, poor MPG..???

Postby Sailing_Faith [OP] » July 26th 2016, 5:30am

A few screenshots (warmed up, parked in driveway)

image.png
1
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Re: Low power, rough idle, poor MPG..???

Postby Sailing_Faith [OP] » July 26th 2016, 5:36am

Oh, and a family emergency has me leaving to drive 2,500 miles tomorrow (San Francisco Bay Area to Pensacola, Fl......

I suppose I'll drive past several members here... Thinking of taking I-70 or I-40... I-10 is a real challenge in this heat! (I camp inmy van)....
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Re: Low power, rough idle, poor MPG..???

Postby Wimpazz » July 26th 2016, 6:35am

My similar issue was solved by...
1) seafoam/ magic smoke trick (stuck exhaust valve due to narrow valve guides + crud)

2) replacing crackled plug and leaking wires. Have you tried water spray in the dark and watched for fireworks?
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Re: Low power, rough idle, poor MPG..???

Postby sadglad » July 26th 2016, 9:24am

My sad old gladiator conversion van had the same symptoms. Turned out that one spark plug with a hairline crack in the porcelain.
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Re: Low power, rough idle, poor MPG..???

Postby Astrofarian » July 26th 2016, 12:07pm

In the absence of any other clues, I have to side with the last 2 replies. When all the newfangled gizmoids fail to provide any help, go with the basics. Try the water mist trick in a dark environment and go from there. Hope all is under control with your family. :pray:
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Re: Low power, rough idle, poor MPG..???

Postby Surfin Safari » July 26th 2016, 3:02pm

Get a couple of bottles of Techron. Just before your next fill up with a nearly empty tank dump in a bottle in then fill up. Do that on the next 2 fill ups. Make sure your AC is working good, you are going to drive through a couple of heat waves. I am currently in the East bay taking a break from the Florida heat. Heading back on Thursday. Good Luck.
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Re: Low power, rough idle, poor MPG..???

Postby Sailing_Faith [OP] » August 2nd 2016, 2:43am

Thanks for the replies.

So I drove it from CA to FL with the problem, no relief of the symptoms (extra gas cost me about $135).

Surfin, you were sure right! Saw 114f south of Las Vegas! Hotter then all get out all the way.... Glad to have a good fan for sleeping. :rockon:

Two votes said cracked plugs. I replaced the AC Delco platinum tips with 21k on them (I would expect to get 70k)... No change, insulators were nice and even color.

Of course I did the nighttime check for sparks, both with and without water spray,,, did not see anything. Even went out on the road at night with the doghouse off.

I pulled each of the plug wires and read them with a meter. Two were significantly higher then the rest (again, only 21k on the AC Delco brand wires, but I know these vans eat them).... :chevy:

I read out each wire before install, and coated both ends with dielectric grease as in my habit....

No improvement. :whack:

Just did a 121 mile road test, and got 15.1 mpg at a leasurely 62mph.... :banghead:

Fuel trim is staying in the same range, just no power... Poor mpg, and rough idle.

Thinking out loud, I am not thinking low fuel pressure, or dirty injectors since that would show up in the fuel trim (it would create a lean condition that the computer would increase fuel trim for right?)... Plus it has a brand new (updated) spider.

I do notice a very slight miss on the highway, mostly at a constant speed (weird huh?)
When it happens fuel trim goes slightly positive... But never more then 8%.

I hate just throwing parts at it, but I am thinking of replacing the coil next... :shrug:

Thanks for the comments, and suggestions. :ty:
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Re: Low power, rough idle, poor MPG..???

Postby Surfin Safari » August 2nd 2016, 3:21am

Where abouts are you in the Sunshine State? I might be able to lend a hand
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Re: Low power, rough idle, poor MPG..???

Postby Leeann_93 » August 2nd 2016, 3:29am

If I'm reading your O2 sensor data above correctly, there's weirdness with the passenger side front sensor (B2S1). It's reading really low, especially compared to B1S1. When's the last time you looked at your O2 sensors (without lazy me going back through the thread)?
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Re: Low power, rough idle, poor MPG..???

Postby Sailing_Faith [OP] » August 2nd 2016, 3:44am

Leeann_93 wrote:If I'm reading your O2 sensor data above correctly, there's weirdness with the passenger side front sensor (B2S1). It's reading really low, especially compared to B1S1. When's the last time you looked at your O2 sensors (without lazy me going back through the thread)?


I have been working on passing California emissions, and replaced the upstream sensors... I can't believe I did not notice that, but tht is why I posted.

I had bought them a while back , and on opening the packages (Delco) I found one upstream, and one downstream :banghead: They were in boxes w the same part numbers, so I just bought one more... And it was Bosch (yea, I know)...

I'll check the numbers again, then swap them side for side... If the weird numbers follow I'll replace the bad one (I bet it will be the Bosch!).

I might have to drive out your way to buy you a frosty beverage!
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Re: Low power, rough idle, poor MPG..???

Postby Leeann_93 » August 2nd 2016, 3:51am

Oh, I might lay money on the Bosch.

A frosty beverage would do quite nicely, though - if I'm right!
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Re: Low power, rough idle, poor MPG..???

Postby Wimpazz » August 2nd 2016, 5:59am

x2...on the frosty beverage that is.... I'm John Snow here, i know nothing.
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Re: Low power, rough idle, poor MPG..???

Postby Surfin Safari » August 2nd 2016, 4:05pm

Register your Van in the sunshine state while you are here and you will never have to get smogged again.
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Re: Low power, rough idle, poor MPG..???

Postby Sailing_Faith [OP] » August 2nd 2016, 4:14pm

Surfin Safari wrote:Register your Van in the sunshine state while you are here and you will never have to get smogged again.


I have Florida tags, I have property here but have been mostly living in California for almost two years now.... I am still technically legal, I have driven the van out of state several times now... I just know eventually I'll get busted. :naughty:

By the way, thanks for your offer. I am in the panhandle, north of pensacola. I will drive to Orlando before I head back across the country.... I have driven across 6 times with this van now. Last year I made a little detour up to Cape Cod (then back to Fl!) just for fun.

It's really all just about my sustained efforts to get into the :bow: "Quarter Million Mile Club".... I always wanted to be one of the cool kids. :thumbup:
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Re: Low power, rough idle, poor MPG..???

Postby Sailing_Faith [OP] » August 11th 2016, 8:00pm

I do so wish Leann had been right.

I rechecked the numbers, after several checks, I did not see that low o2 voltage.

Now you see it....
image.jpg


Now you don't
image.png
Good


Swapped the sensors anyway, still nothing out of line.

Even tried putting the old sensor in place of the Bosch.

So I drove it from CA to Florida....

Hauled a load of hay for my mothers goats, did a bunch of chores towing a trailer...

And started driving back across the country.

All while getting around 15mpg.

Last night while driving through New Mexico I noticed a very faint miss.

I had actually grabbed my spare Coil while I was in Fl.. Just now tried swapping it out.

Wish me luck (of course I will fix it with less then 1,000 miles left on an over 6,000 mile road trip! :dunce:
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Re: Low power, rough idle, poor MPG..???

Postby Sailing_Faith [OP] » August 11th 2016, 9:24pm

The idle is much more smooth, and the faint miss seems to be gone. :banana:

I'll update after my next fill up.

Winslow, AZ

image.jpeg
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Re: Low power, rough idle, poor MPG..???

Postby Leeann_93 » August 11th 2016, 10:40pm

Such a fine sight to see....



Yeah, I wish I was right. A bad coil isn't that much of a surprise, though.
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Re: Low power, rough idle, poor MPG..???

Postby juststartin » August 17th 2016, 4:04am

Was it confirmed to be the coil?
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Re: Low power, rough idle, poor MPG..???

Postby Sailing_Faith [OP] » September 7th 2016, 2:11am

juststartin wrote:Was it confirmed to be the coil?


Yes, absolutely. :banana:

After changing the coil out with a new one I just happened to have picked up from my shop... the MPG was between 19.5 and 20.8 the rest of the trip.

The minor miss was gone. :driving:


So, now a few weeks later I am getting a miss on acceleration. I was reading in another thread and ChevyMahler posted this (Quoted here for clarity);

chevymaher wrote:.......

On the new coils did you grind the paint away from the mounting points so it has a good ground. A bad ground does overheat the windings.

.......If the coil is fried again. I took a wire wheel to the mounting points untill it was clean shiny metal before I mounted it. Same thing on the bracket where it mounted to the intake.

I would toss a 15 dollar computer temp sensor on at the same time just so you know it is good to.


You know, sometimes I read common sense advise like this on this site and I wanna slap my forehead.... this is a perfect common sense solution and I bet you are right. :rockon:

Having 'fixed' my problem (slight miss, not enough to set a code but enough to really lower MPG) by changing the coil... It is now back. I bet the poor ground (new coil was painted up all pretty)....

Thanks Chevymaher.



Now the coil I had was not an OEM AC Delco as everyone recommends, (or is it the Delphi that is preferred?)... but whatever the make, I bet cleaning the paint off of the mounting tabs would both ground it and allow better heat transfer. I'll make sure to do that when the new one goes in.
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