Bizarre Intermittent Power Loss....many parts replaced.....

Over course of the last month or two I've experienced an intermittent loss of power while accelerating. This is in my 91 B2600.

This power loss can only be described as feeling like the engine is 'recoiling' while accelerating. Rapid loss of power, surging back to normal, then stumbling again. The only 'pattern' which I have seemed to identify with this issue is that it has been occurring usually while I have been driving during the hottest time of the day, for excessive (more than 20 minutes) amounts of time. Leading me to suspect something is heating up to the point of intermittent failure.

In the past 3 weeks I have replaced the following:

Fuel Pump (With new Bosch Premium pump)
Distributor Cap and Rotor
and yesterday a new Ignition Control Module (The very small black box mounted near the coil).

Last June I also had replaced the Ignition Coil itself during another unrelated problem.

I suspect this again to be some sort of electrical component overheating until it starts failing due to the fact this issue hasn't reared it's ugly head in the morning or night time hours while it's cooler out. Also, today when this started happening, I was able to find a car wash and promptly hosed down the engine compartment. Sure enough, after I did that, the engine power drops stopped. Again, leading me to suspect something is getting way too hot and failing.

At this juncture i'm considering buying a new coil (even though I did just replace it last summer) or a condenser (appears to be another ignition related part close to the coil).

Any other areas I should be focusing on that would cause such an issue? I've also taken note that despite the dramatic losses of power when this happens, my tach doesnt seem to drop very much, even though power loss does feel rather significant. And one more sidebar, while inspecting the distributor, I noticed after getting fairly deep under the cap, there was a round black plastic ring with an electrical connector sticking out the side of the dizzy. Im not entirely sure what that is even for, or if it could be a component possibly causing this issue too, but did wonder what exactly that is, or controls.

But back to main issue, where should I start? Ive already ordered another coil and this 'condenser' listed on rockauto....

Surely my spraying off the engine bay and the problem going away would indicate something is getting too hot right?

Any and all replies would be greatly appreciated! Thanks.

On the 2600i trucks, the Electronic Control Units are known to go bad, giving all kinds of problems, including some of what you are describing. Cooling the motor might have just caused the ECU to default to a different driving "map" which took it out of the circuit portion that is giving you problems. There are a number of threads on the board about the capacitors that blow on the the ECU, and how to replace them if that is the problem.

In the meantime, you could take the ECU out from under the passenger kick panel, take the cover off of it, and drive around for awhile and see if the problem goes away; improving airflow around the ECU would cool it more and that would isolate your issue, which I would agree is intermittant overheating.

Check and clean the connections for your mass air flow sensor. Dirty connections gave me the very same symptoms. A shot of brake clean and work the plug on and off a few times ought to do it.... if that's your issue.

When the problem first started over a month ago I got a can of MAF sensor cleaner, disassembled everything and thoroughly sprayed it, including connector....the contacts all seemed rather clean. I ruled this out after it became apparent this was only happening after something was getting too hot due to the issue arising after 20-30 min of driving in city heat. Again, after I hosed off engine compartment, problem seemed to go away, leading me again to believe some component is over heating. Think Ecm? And what should I be looking for if I do open that up?

I would suggest you do some research in historical threads posted in the 2600i portion of this board. Basically you are looking for blown capacitors. But that isn't really necessary yet until you take the cover off and drive around to see if it running cooler solves or helps your issue is some manner. You can get a can of cool off and spray the board to see if the problem stays the same.

Check all the connectors for that matter. But I would be hesitant to start hosing down a hot engine.

As for your distributor, I've never seen anything like that. If you can, get a pictures of the connecter and post it. I did talk to somebody one time that bought a replacement distributor. It looked identical to his OEM distributor. It still didn't solve his bizarre ignition issues. Out of curiosity, he pulled the cap and rotor, and then pulled the inner "cover." What he described sounded like a Hall Effect pickup as opposed to his OEM optical pickup. So he sent it back and got it exchanged for an optical pick up distributor. He said they looked identical otherwise.... (it was not an 89 vacuum advance with ignitor, condenser, and vacuum module all on the outside.) I have since seen on a parts company web site (don't remember which) distributors offered for 90+ models and one was a "Hall Effect" and the other an "Optical" pickup. I've personally never seen anything other than an optical style pickup and never heard of a Hall Effect style for these truck until the two instances above.

So if you can post some pictures, I'd really be curious to see what you have. And if you pull the rotor and cover, I'd also be curious to see what kind of pick up you have underneath. How about the distributor connecter? What kind of shape is it in as well the connecter on the harness? A lot of times, those wires are in rough shape where they go into the harness connector.

Another thing I would look at is the main relay. They do go bad in time. I would let the engine get good and hot and then pull over and see what kind of voltage you are getting downstream of the relay. The easiest way to check that is to probe the center connecter with the Black/Yellow Stripe wire in the green six terminal connecter near the wiper motor. That will tell you what voltage is getting delivered to your distributor (crank angle sensor), MAF, injectors, and IAC. It should be essentially the same as your battery voltage - or system voltage with the engine running. If it's much less, then your relay is dirty and/or failing.

You are going to be looking at the two cylindrical capacitors and the area of the board surrounding them. If the board underneath them isn't squeaky clean like the rest of the board, then they have been leaking. Sometimes it's really obvious and you see green corrosion. Other times, the leakage is so faint that owners have looked at them and didn't notice the ever so slightly stained area under the caps. Look close and take some pictures!

I took off the cover to the ECM and sure enough there is an area of the board with a corrosion looking film on it....with a bunch of little black square looking things in this middle of this pool....I assume those arent the capacitors though that caused this. There is one of those vertical 'tube' looking things pretty close to this corrosion though, and it looks like it might have some dried up residual fluid on the side of it....I assume this is the capacitor that might have caused this?

In any event, wherever all this 'fluid' spilled onto the board, are all those small black square components ruined as well or is it just the round tubes that need replacing?

(I assume I have found the cause of my power loss problems??)

(The ECU also appears to be the original stock one from 91....stamped with Mitsubishi logo and no indications it was a rebuild. )

VERY IMPORTANT: Does anyone have a schematic with component details for the ECU? Before I attempt any repairs.....

Before you attempt any repairs, why don't you try driving around with the cover off to see if the extra air flow keeps the board cool enough to keep the problem from re-occurring, first, instead of assuming yourself into a lot of extra work?

I understand your thinking and I will try this...but....if the parts on the ecu are dead....i don't think cooling them anymore is going to make it any better right? Somethink def burst and there is a pretty good spot with acid or whatever comes out of those capacitors already on the board.