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Old 10-08-2017, 11:38 PM   #1
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Default Xplorer gas milage

I took the camper on a 300 mile trip this weekend. Keep in mind the wind was blowing harder than I've seen in a long time . The Dodge was a handful even at 55 to 60 mph .
But I only got 8.9 mpg that's horrible.
I'm wondering if I should start replacing parts.
Start off with
new plugs and wires.
possibly replace the Coil , it's the original
possibly the brain box. computer.
Sometimes when you floor it It bucks and stumbles, let off it and floor it again and it's fine.
Hummm.
oh I very recently had the Rochester 4 barrel rebuilt. It seems to run really well.
Any thoughts ???
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Old 10-08-2017, 11:55 PM   #2
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I took the camper on a 300 mile trip this weekend. Keep in mind the wind was blowing harder than I've seen in a long time . The Dodge was a handful even at 55 to 60 mph .
But I only got 8.9 mpg that's horrible.
I'm wondering if I should start replacing parts.
Start off with
new plugs and wires.
possibly replace the Coil , it's the original
possibly the brain box. computer.
Sometimes when you floor it It bucks and stumbles, let off it and floor it again and it's fine.
Hummm.
oh I very recently had the Rochester 4 barrel rebuilt. It seems to run really well.
Any thoughts ???
One of the best ways to tune a carb setup these days is to install a wide band (lamda) oxygen sensor style air fuel mixture gauge. It takes out nearly all the guessing and allows you, or whomever is tuning it, to dial it in very tightly. It is very likely that the carb was not properly setup, as almost no one knows how to do it anymore, especially using modern gauges.

Hopefully, jets, power valves and pumps are available for the Rochester, but they may not be, as you would likely need some for adequate tuning. The oxygenated fuels make tuning a carb tough as you have to be a bit richer in mixture to get the same AF ratio, and it will change if you get pure gas.

If you can't get parts or get tuned well, changing to a more tunable and modern carb and intake would likely pay for itself. On the Chrysler small blocks like a truck 318, I like a 600cfm Holley spread bore 4 barrel, or even a 500cfm two barrel, on an Edelbrock Performer dual plane intake. We have seen over 25mpg in some of the smaller old cars with that setup, even with the rest of engine still original and old.

For the handling, get to a suspension shop and have them look for bad parts, as on an 88 there are nearly certain to be some.
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Old 10-09-2017, 02:54 AM   #3
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One of the best ways to tune a carb setup these days is to install a wide band (lamda) oxygen sensor style air fuel mixture gauge. It takes out nearly all the guessing and allows you, or whomever is tuning it, to dial it in very tightly. It is very likely that the carb was not properly setup, as almost no one knows how to do it anymore, especially using modern gauges.

Hopefully, jets, power valves and pumps are available for the Rochester, but they may not be, as you would likely need some for adequate tuning. The oxygenated fuels make tuning a carb tough as you have to be a bit richer in mixture to get the same AF ratio, and it will change if you get pure gas.

If you can't get parts or get tuned well, changing to a more tunable and modern carb and intake would likely pay for itself. On the Chrysler small blocks like a truck 318, I like a 600cfm Holley spread bore 4 barrel, or even a 500cfm two barrel, on an Edelbrock Performer dual plane intake. We have seen over 25mpg in some of the smaller old cars with that setup, even with the rest of engine still original and old.

For the handling, get to a suspension shop and have them look for bad parts, as on an 88 there are nearly certain to be some.
I'm getting 12-13 on mine, but it has fuel injection.

The Dodges are notorious for poor handling unless you have the dualies. Mine also has the Helwig sway bars, which are substantially bigger than stock. You could look into getting better sways. At a minimum, your bushings and shocks are probably worn out and you might get some improvement replacing those.
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Old 10-09-2017, 11:25 AM   #4
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Your Dodge most likely also has the old style carb heat on it, where the pass exhaust through the intake manifold under the carb to produce a hot spot for better fuel volatility and atomization. If you do have the system, there will be passage from one side of the manifold to the other, head to head. A rotating valve in the exhaust manifold blocks the exhaust on one side, pushes it through to the other side, heating the manifold and carb in the process.

The passage under the carb, through the manifold, are famous for plugging up solid and that can serverly affect milage and cool weather driveability.

You probably would do well the get one of the service books for yor van, as they will show a lot of what you have and aren't very expensive.

Intake manifold clogged with carbon? - Dodge Ram, Ramcharger, Cummins, Jeep, Durango, Power Wagon, Trailduster, all Mopar Truck & SUV Owners. Dodgeram
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Old 10-09-2017, 01:06 PM   #5
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Thank for the responses. I have the new style carb with electric choke, so no crossover on mine. The choke is all new. And seems to be just fine. And I have a original Dodge shop repair manual.
I also had an old school machanic ajust the carb after i installed it. He went through it an said it was all good no leaks.
Think I'll do a complete tune up on it.
Oh an i gota check the EGR valve for operation. That could be stuck im told.
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Old 10-09-2017, 01:30 PM   #6
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Even though you have an electric choke, it is likely that you still have the crossover passage and heat riser valve. It is also what feeds the EGR valve, so if it is plugged changing the valve won't change anything.

You choke could also be a combo choke that uses electric assist to get the choke off faster when the engine is warm, but also uses manifold heat. Chrysler used the combo versions for quite a while, but I don't know when they stopped.

You sag on acceleration is likely due to accelerator pump adjustments, but also could be vacuum advance. They did some backwards vacuum advance stuff for a while that could be a mess to figure out and get running right. Of course the EGR could also cause sags.

You have the latest carb used, I think, as the throttle body version fuel injection came out the next year, and they were severely struggling on emissions stuff. Being a Rochester and an emissions carb (likely) there will be very few adjustments or modification parts available for it. Your mechanic was probably only able to set float level, and do some restricted idle mixture tweaking. There would probably be a lever to bend for accelerator pump shot that will be on the primaries only but no real volume adjustment. If you have to run 10% ethanol, you are going to have mixture setting issues with any of the pure gas designed and setup emission carbs from back then.
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Old 10-09-2017, 02:00 PM   #7
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I know he was able to adjust the two mix screws under the front of the base plate. The rebuilder opened them up. The rebuiler told me which mix screw to adjust with a vacuum gauge on it. Said make it read 18".
Of course the mechanic said I dont need no stinking gauge. Lol
Oh my choak is totaly electronic. No assist
I will check to see if the egr valve moves.
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Old 10-09-2017, 02:19 PM   #8
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Also check to make sure the egr gets hot to indicate exhaust is going through it. I think it sits right in the middle of the manifold right at the r/h head?. You should also be able to feel the manifold right there to see if it gets hot right away when you start the engine. The egr will sometimes, but not often, move but still have the passages plugged so no flow. If you remove the egr, you will be able to see if things are plugged below it, which is an easy thing to do unless the bolts are rusted in.

I think you have a Quadrajet, so the two screws in the base IIRC are for idle mixtures. It will use metering rods for enrichment with a main jet on the primary and they sometimes can be tweaked to richen sooner or later. The rods are changeable to get different main and enrichment profiles, but the rods are likely very hard to find. Secondary is likely through a fixed orifice with a rod to meter. The adjustment they talked about is to adjust the opening of the air valve in the secondaries, and from what I have always been told by the gurus who used them a lot, is the most critical adjustment on a Quadrajet, and the hardest to get right, even with a vacuum gauge and pump. It determines secondary tip in, so easily could cause you sag.
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Old 10-09-2017, 06:14 PM   #9
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.

If you drive by the vacuum gauge,
you can drive more conservatively and, increase your gas mileage.

You can get the vacuum reading through the OBDII reader.
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Old 10-12-2017, 01:58 AM   #10
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.

If you drive by the vacuum gauge,
you can drive more conservatively and, increase your gas mileage.

You can get the vacuum reading through the OBDII reader.
1988 No OBD connector
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