88MM bucking/surging/stalling at part throttle... sometimes

[88MightyMax]

Hey all,

Someone just donated an 88 Might Max to our church, and since I'm the only mechanically inclined person there, I get to fix it. :)

When I started driving it, it ran just fine through town for a couple days. Then I had it act up. When it does, it surges/bucks/seems to cut out, and sometimes stalls. When it stalls it always restarts immediately.

I found if I kept it either floored, or with no throttle at all it would run ok. At part throttle it acted the worst. WOT would take a couple seconds to clear up, then it would accelerate well.

It only has 78k miles on it. I presume everything is still stock on it.. I was going to do a general tune up (plugs/wires/cap/rotor), but haven't gotten to it yet.

It doesn't sound like spark to me, since it clears up and runs pretty well at WOT, and always restarts. Do these trucks have points, or some other electronic ignition?

I would think the fuel supply is fine, since I drove another ~8 miles with it acting up. (Unless I'm pushing too much pressure and overflowing the floats?)

My guess would be the carb? I did the redneck carb clean by revving it up then blocking the intake a few times. I also put some seafoam in the tank to see if it can break anything loose in the carb.

Thanks for any ideas!

[pennyman1]

you have vacuum leaks - check the hoses, especially the ones going to the silver box on the drivers side inner fender. Those hoses split and/or mice eat them and will cause that issue.

[88MightyMax]

Thanks for the reply.

Just did a cursory examination of them, but didn't see anything obvious. It looks like the entire vacuum harness was designed to come out? I may take some notes, then pull the whole thing out for a better inspection one of these days.

I may also just replace them all one-by-one, if that's mostly guaranteed to fix the issue.

However, I did just come across a Weber 32/36 DGAV carb on my shelf I accidentally won on ebay several years ago. Needs rebuilt, but I'm thinking it would fit?

[pennyman1]

it would with the adaptor kit - will make a world of difference on that truck.

[pennyman1]

the ones in the box are notorious for cracking - I had an 88 that decided to split the main big hose in that box on a return trip from columbus ohio to pittsburgh - not a fun trip on an interstate with 2 engines in the back and several steep hills to climb at highway speed.

[88MightyMax]

"In the box" - are there more vacuum lines in that silver box?

The truck will mainly be an around town truck, so it just needs to work. If I can't find the errant vacuum line(s), a swap may be in its future :devil2:

[pennyman1]

there are several - the box contains a sensor that sends signals to the computer controlled carb to adjust the working of it. A leak to that sensor throws the carb into an erratic state. The weber carb install gets rid of all that and gives you a simple easy to work on unit. Are you going to say the devil made you use a weber on a church truck? Hmmmm...

[88MightyMax]

Good to know. I'll check in there tomorrow.

The swap is tempting... I'll have to check my carb tomorrow for throttle shaft play. See if it's even worth rebuilding.

A conversion kit from Redline is probably $350ish?

[noahwins]

I have a complete stock emissions system from an '89 2.0, including all the line and the stock carb that worked fine, even if it wasn't terribly "performance oriented." I'm converting to diesel and don't need it anymore. If this is for your church and not personal use, you can have it. Just pay for boxing up and shipping.

[88MightyMax]

Got the silver box out, and the internal lines appear fine.

However, the large vacuum line (the one with a hose clamp) is very soft, and appears to have been folded shut (occasionally?) where it went through the foam loom that's bolted to the inner fender. I'm assuming that won't help anything, lol. I'll start by replacing that.

Noah, depending on how my troubleshooting goes, I may take you up on that offer. :cheers: It'll be used by the pastor to drive around town doing his 'pastor-y' things, so he doesn't have to use his personal car anymore.

[88MightyMax]

With my extra hour of sunlight a few nights ago, I got the big hose to the silver box replaced. It completely collapsed when I used my Mity-Vac to put vacuum in it.

Drove the truck today, and it still kicks & bucks :( Not near as bad, but it still isn't normal.

So, I'll weigh my options between swapping to a weber, and swapping everything over from noah.

Thanks for the feedback thus far.

[BradMph]

I see something religious here, lol. Noah, (first man)..also builds arks pretty good, then making an offering to the church. This is too coincidence...lol.
Noah, your going to heaven if you like it or not. :grin: †


88MightyMax, swapping to weber is a removal of smog stuff. How does your state of Oregon feel about smog laws on your vehicle? is it exempt from smog test? if not...Noah's offerings sound extremely good. If your state has the vehicle as exempt from further smog testing, then by all means go weber and remove the plumbing that feeds the engine it's own poop over again. (smog devices)

[88MightyMax]

Noah, thanks for the offer, but I ended up splurging and buying the conversion kit.

Now I have a few questions:

1. I have two fuel lines from pump, like this:

http://www.mightyram50.net/vbulletin/attachment.php?attachmentid=4719&d=1360789973

I also have another return line on the drivers side fender. I'm assuming I can just connect the line on the fender to the return port on the fuel pump? I'd really like to avoid having to get an electric fuel pump.

2. My distributor has two vacuum lines on the vac advance. Which one should I use? I have not hooked up the mity-vac yet to see if they pull the rotor different directions.

3. The install guide says to use grease, or to soak the gaskets in oil. I was not expecting this, lol. I have a couple kinds of axle grease. I guess that should work ok?

[88MightyMax]

Ok, I have the adapter plates mounted, and have another question:

4. The 'tree' under the carb that has 5 vacuum lines going to it. I presume they will need plugged? I could find out when I start it the first time, but I'd rather do it now if I have to.

And, I'll need a throttle linkage adapter like Ramshorn did in his thread.

[88MightyMax]

Got it all back together and running well this weekend. "Wow, it has so much power, and it'll even do 65 now" :thumbup:

To fill in my blanks;
1. I looped the return line to the return line on the pump. Also used a 1/4" fuel line from the pump to the carb, with an inline filter, so hopefully that will cut the pressure down a bit. Seems to be working just fine.

2. I hooked up my mity-vac, and the port nearest the distributor has much more advance than the farther one. So, I used the nearer one.

3. Used axle grease. Seems to work. Will make it very easy to clean if the carb/adapter plates ever have to come off again.

4. Yep, the tree has vacuum. A pack of plugs fixed that. I also plugged the 1/4" nipple near the EGR valve.

Electric choke: The plug to the old carb had a large red wire that went to the choke. But, it didn't have power when keyed on? The two white/black wires in the same plug did though. So, I cut the harness off the old carb, then spliced the big red wire into the two smaller white/black wires, and ran that to the electric choke.

And I did need to order the throttle linkage adapter.

Thanks for the help :cool: