Gas Mileage

[PlayingWithTBI]

So I got an ACCEL supercoil. Advertised faster starts, better power, and mpg.

Here's what I got out of an Accel coil after 6 Months on my 88. The engine started to die when I ran it through the car wash and idle was a little choppy. Now I'm running an AC Delco GM Genuine coil - no issues. YMMV

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[Nick88]

Here's what I got out of an Accel coil after 6 Months on my 88. The engine started to die when I ran it through the car wash and idle was a little choppy. Now I'm running an AC Delco GM Genuine coil - no issues. YMMV

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Sorry the picture is small, I can’t really see, is there a hole burnt through causing a short? On mine, I noticed some black around the edge of the metal frame on the yellow, but I wiped it off and it hasn’t come back. I’ve read a lot of ACCEL horror stories, but also heard a lot of good, seems like quality control overall has lowered. I’ll probably switch to Delco if the ACCEL fails out of warranty.

 

[PlayingWithTBI]

Sorry the picture is small, I can’t really see, is there a hole burnt through causing a short?

Yes, I put a circle around where there's a black spot just under the iron which gave me an intermittent rough idle and shorted completely when I went through the car wash. I found it by spray some water around on the ignition system and, when I sprayed the coil, the engine died.

 

[Road Trip]

Here's what I got out of an Accel coil after 6 Months on my 88. The engine started to die when I ran it through the car wash and idle was a little choppy. Now I'm running an AC Delco GM Genuine coil - no issues. YMMV

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A lot of GMT400 owners don't realize that when you task a single ignition coil to feed
high KV pulses/sparks to all *8* cylinders, that if the very best materials & manufacturing methods
aren't used, sooner rather than later in this high duty cycle environment the coil will lose control
of all the bottled lightning inside.

One of my new favorite videos shows a single-headed SBC 350 blinding a couple of experimenters
with science. Although this is an older 'coil in cap' HEI ignition, it's neat to see the sparks leaking out of one
of the unused spark plug wire terminals at least 3 times in dramatic fashion on the 2nd engine test firing:

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(Note: My theory is that the missing wires caused the HEI internal voltage to climb to max. Despite our efforts to the contrary, High KV HEI electricity will not be denied. :0)

IMO, here's the single best 20 second SBC motorhead training video currently on YouTube: Single headed V8 with thunderbolt HEI display

And like you did, troubleshooting an intermittent coil issue by lightly misting it is a valid/productive test procedure.
Right up there with watching for visible sparks in the engine bay on a dark night or in a lights-out garage. Or
happening to hear that sharp HEI stray snap sound. Just don't become part of a stray HEI discharge path -- it will
light you up. :0)

Who knew that all things having to do with ICE ignition could be so interesting?

 

[CumminsFever]

I once owned a '93 s10 with tbi 4.3 and 5 speed. In stock form it gave me 19mpg with mostly highway driving. I deleted the cat, put a free-flowing 2 1/2" muffler and tailpipe on it, GM performance (low resistance) wires, and delco rapid fire plugs. Installed a msd high-voltage coil too. I also messed with fuel pressure regulator, giving it a bit more pressure. I saw 22mpg from then on. It seemed to have a bit more low rpm power.
From my experience, I can believe OP claims, but again, who's to say the same wouldn't have resulted from replacing the same parts with standard new ones?

 

[Nick88]

I once owned a '93 s10 with tbi 4.3 and 5 speed. In stock form it gave me 19mpg with mostly highway driving. I deleted the cat, put a free-flowing 2 1/2" muffler and tailpipe on it, GM performance (low resistance) wires, and delco rapid fire plugs. Installed a msd high-voltage coil too. I also messed with fuel pressure regulator, giving it a bit more pressure. I saw 22mpg from then on. It seemed to have a bit more low rpm power.
From my experience, I can believe OP claims, but again, who's to say the same wouldn't have resulted from replacing the same parts with standard new ones?

Very possible, and I really have no way to know, but my numbers are higher than the factory rated fuel economy specs, which many even call wishful thinking. It could be just worn parts fixing up making it run better and more efficient, which I don’t doubt, but the numbers are much better, so who knows.

 

[GMCTruck]

Best modification to increase gas mileage is to drive with a tail wind.

 

[Caman96]

The 33” Mud Terrains and 3.73 gearing have me questioning this. Who adjusted pcm for tire size?

 

[L31MaxExpress]

Best modification to increase gas mileage is to drive with a tail wind.

The best way to kill economy is drive 80-85 mph into a 15-20+ mph headwind too.

That being said when I was in Colorado and also New Mexico at over 1 mile elevation and at times over 2 miles, my little Pathfinder was getting 2-3 mpg better than it has ever gotten here in Texas. I crunched some quick air density numbers and the 4.0L effectively becomes a 3.0L air consumption thus fuel consumption wise at 2 miles elevation.

 

[L31MaxExpress]

The 33” Mud Terrains and 3.73 gearing have me questioning this. Who adjusted pcm for tire size?

It is an early TBI. Those had a speedo cable up until GM started adding rear wheel antilock brakes.

Most of those V-series trucks and SUVs had 31s from the factory and a 33" tire would actually make the vehicle show less mileage for a given distance.