'88 2.6 MM issues starting

[Evelyn_]

Hey there folks!

I have an '88 Mighty Max with the 2.6 and a Weber 38 on it. A few weeks ago, I was driving to the store just fine, then when I got back in the truck 20 minutes later it wouldn't start. Had to get it towed home, and it's been sitting ever since.


Here's what's happening:

When I try to start the truck after it's sat for about a day or two, it'll fire one cylinder then immediately cut back out. After that, it'll just try to crank to no avail. Before adjusting the float it would spit fuel out of the top of the carb, but that appears to be fixed now? The choke valves seem to be getting a little wet when trying to start it, but it's not visibly shooting out anymore.


So far I've:

- Confirmed that there is spark and fuel
(Fuel - Pulled the fuel line from the carb and made sure it was spraying as intended)
(Spark - Stuck a screwdriver in all 4 plug wires and held it close to the chassis, all 4 arced)

- Fixed the carb float level (40mm closed, 50mm open? It was at 35/40mm respectively)

- Cleaned the needle and seat (didn't see any dirt in there but did it anyways)



This is my first carbureted vehicle so I'm a bit out of my element, and I'm not really sure what to try next.


Thanks!
-Evelyn

[SubGothius]

Hm, wet choke butterflies seem odd, as there shouldn't be any fuel that high up in the carb. That along with fuel spitting out the top earlier leads me to wonder if excess fuel pressure may be forcing fuel past the needle valve, causing flooding.

If you pull a spark plug or two right after it won't start, do the tips look wet or black with carbon? That would confirm a flooded or rich condition, respectively.

Fuel "spraying" out of the disconnected supply line seems excessive, but maybe I'm reading too much into your word choice there; low pressure suitable for a Weber would flow out evenly but not shoot far with any force.

What's the fuel pump setup? If it's still using the stock mechanical pump attached to the head, does it feed thru a fuel pressure regulator before the carb? If so, maybe the regulator failed. If it has an electric pump, it might regulate pressure with an internal bypass valve that got stuck closed somehow.

[Evelyn_]

The plugs are definitely black around the base and smell of fuel when I pull them out after trying to start the truck. Sure seems to be flooding, I'll try replacing the fuel pump in case it's running a bit strong (I'm not sure when this was last done.) When I pulled the line off I noticed that it was pouring pretty quickly, it filled up an 8oz cup in like 10 seconds at most, though I'm not sure that's unusual. Either way, worth a shot! Thanks for the info

[SubGothius]

If it's an electric pump, I like the Carter P90091. Quiet, reliable, smooth fuel delivery, and native PSI is perfect for Webers.

[Pengineer1]

I've also got a 2.6l with a Weber 38. Soon after I swapped the carb I shut it off and couldn't get it to start minutes later. Evidently it sorta backfired when I shut it down but didn't notice. The backfire stuck the choke butterfly closed so that it was suddenly choking off the air and bringing in way too much fuel. I tapped the butterfly free and she started and ran and has never done it again. Have you checked your choke butterfly?
Bill

[Evelyn_]

Thanks for the info Bill! I did notice that the choke butterfly didn't appear to be opening at full throttle, but I wasn't really sure if that was intentional or not considering it has an electric choke. I'll give that a shot!

Additionally, I resistance tested my ignition coil and realized that that was reading 15.2KOhms instead of the 27KOhms that it was supposed to be reading, so that may have been the problem as well lol. Getting a new coil today so hopefully we'll be good to go!

[Evelyn_]

Well, unfortunately the truck still isn't running. Definitely seems like the ignition coil, unfortunately after getting 2 more coils (one from a junkyard, one from O'Reilly) neither one is reading correctly.

The junkyard one, as expected, is shorted out and not giving any reading on the secondary winding at all, meanwhile the new one from O'Reilly is only reading 11.3Kohms on secondary, which is even lower than the NGK coil that was in my truck to begin with at 15.2KOhms.

Does anyone have any recommendations on 12v ignition coils, or does anyone know if a more modern coil reading 11.3Kohms may be okay?

Thanks so much everyone!

[SubGothius]

I got this Herko B108 coil a few years ago, been working fine ever since:
https://www.ebay.com/itm/381825243549

BTW, I dis/reassembled the mounting bracket to put the resistor block on the other side, which allowed for more convenient and tidy wire reach/routing. Secondary coil resistance reads at ~20.5k Ohms just now.

I'm not sure those variances in coil resistance are significant enough to make much effective difference, esp. for aftermarket coils more likely to vary from OEM units; as such, we might consider the spec a ballpark idea of what to expect (something in the low tens of kOhms), so only a wildly different reading like sub-k Ohms or 100+ kOhms would suggest something seriously amiss.

Choke butterfly opening isn't really affected by throttle opening, just the bimetallic spring in the choke element that heats up and rotates the linkage over time (electric choke) or as the coolant warms up (aqua choke).

[Evelyn_]

Gotcha! I unstuck the butterfly today and tried to fire it off with the new ignition coil but no luck, even with a liberal amount of starting fluid. One of the plugs was wet when I pulled it out, so I'm gonna give it another shot tomorrow and see if I get lucky!

P.S. I'm so happy I found this forum lol. Best one I've ever been on!

Thanks folks,
Evelyn

[geezer101]

Are you getting actual spark discharge from the leads? The transformer coil you have been recommended is the way to go as they generate a stronger spark over the oil filled coils. If you're getting a good, visible spark from all leads I would try regapping the plugs to 0.85-0.9mm. If you're getting no spark then you might have to consider the ICM in the distributor has failed. These modules are available and easy enough to replace. Good luck. No start/running issues are frustrating to deal with...

[Evelyn_]

You know, I hadn't actually tested spark from the ignition coil in about a week after trying to replace the coil. Turns out I'm not getting 12v to the coil, so I get to trace that back tomorrow and see where that gets me. As frustrating as this has been, it's definitely been a learning experience!

[1fastcolt]

hands on and diagnosing is the best way to learn... its a pita but once u get the basics down it will stay with u the rest of ur life.. huge thumbs up to trying and learning..

[Evelyn_]

I think I finally figured it out.

At first, I noticed that it was flooding, and I checked fuel and spark, both of which were good. From there, I took the carb apart and checked everything in it, EXCEPT the choke valves. Shoutout to Pengineer1 for calling it. Unfortunately, missing that at the time led me to take a look at the ignition system, leading me to the issues so far in this thread. I fixed the carb choke valves two days ago, but three days ago I accidentally reversed the polarity on the ignition coil ballast resistor, frying a couple wires, unbeknownst to me at the time. If I hadn't done this, the truck probably would have just fired up with the choke valves being fixed, but you live and learn I guess.

Yesterday I realized that there was no longer spark, and after screwing around with the ignition coil a bit more today, I decided to make sure that the ignition coil was still getting 12v when being started, and lo and behold it wasn't. I then tried to take the ignition switch b/w wire and put it directly on the positive terminal of the ignition coil to see if bypassing the ballast resistor would start the truck, as I read about on another forum post here:

"If you want to do away with the resistor just run the B&W 12v to the coil (+) and the B&W dizzy wire to the same post. The B&W is switched and has power both in the run and start positions. The B&R can be cut, shrink wrapped, and tucked away." - shorturl.at/BCUX3

I still didn't get the truck to spark when doing that, but that led me to realizing that I had indeed shorted the wires. I then traced the ignition switch b/w wire and the b/r wire that connects to the positive terminal on the ignition coil via the jumper on the ballast resistor. Both are most likely fried as a result of reversing polarity, but I plan to just fix the b/w wire for now just to get it running by bypassing the ballast resistor as the above post suggested.

I'm going to replace the ignition switch tomorrow as a shortcut to fixing the b/w wire (it still engages the starter and turns on the radio, so I know that it's only the one connector on the switch that's shot, and that I could fix it for cheaper than it is to get a new switch, but I just want this to be over with.) I'll let you all know if that's the ticket to get my baby running again!



Thanks for everyone's help! This forum has been absolutely invaluable as a resource, especially for someone with an interest but very little experience diagnosing issues with cars. I've replaced my fair share of parts before, but I've always just had an OBD2 sensor to plug into, lol.

[geezer101]

Don't run it for long without a ballast or you'll risk roasting something downstream of the coil.

[SubGothius]

Just to clarify, the B/R wire only gets power while cranking the starter. This bypasses the ballast resistor to give a bit of extra spark oomph for starting, but as geezer noted, bypassing the resistor for regular driving can burn something out prematurely.

The B/W wire gets power whenever the key is in the Run and Start positions, and this feeds thru the resistor to power the coil at a reduced voltage for regular driving. I wonder if you may have burned out the ballast resistor at some point? It's just a coil of high-resistance wire inside a ceramic heat shield, so if you don't have a multimeter or test light handy to check it, you can just remove it and inspect to see if that coiled resistance wire is broken. The Herko B108 coil I recommended above comes with a new ballast resistor.

[Evelyn_]

Thanks guys!

I tested the coil and ballast resistor again this morning (turns out my old multimeter was hit or miss, so I picked up a new one) and everything appears to be okay EXCEPT that I'm getting 9v to both the b/r and the b/w wires when trying to start the truck instead of 12. Not sure exactly how that would happen, as the battery is reading 14v. Any ideas? It seems like every time I round a corner and figure out something, it either ends up being wrong or not the core issue Happy to be learning though!

[SubGothius]

Hm... how's the condition of your battery terminals and their cable clamps? Try removing the clamps, clean them up along with the terminals using one of those innie-outie wire brushes, available at any auto parts store for a few bucks.

[Evelyn_]

I figured it out! Turns out I fried the ignition control module at some point. Replaced it and it fired and ran! Ignition timing is a bit off, so I'm gonna get that dialed in this evening but it's working! Thanks so much everyone.

[geezer101]

The tune specs for US trucks is a little soft. You can play with the tune and plug gaps to gain some performance. The Australian tune specs are slightly more aggressive (emissions regulations aren't as rigid here)