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Discussion Starter · #1 ·
Coming in for advice because I've been battling this thing for a couple of weeks....

The engine is an AEB from a '98 Passat swapped into a '75 VW Bus. Engine was gone through before installation, new gaskets (including head), new seals, timing chain tensioner, timing belt. Didn't mess with the ancillaries much at that point, same TB, injectors, turbo, coils &etc that were in the donor Passat because it had all been working fine.

Looking with VCDS I'm seeing a persistent random misfire across most/all cylinders at low (under 1200ish RPMs) that I can't seem to shake. I started with replacing the ICM, plugs, MAF. Swapping coils around didn't seem to move the misfire frequency from one cylinder to another, and even swapping in a couple of new ones didn't change anything. Couldn't find a vacuum leak anywhere with starting fluid, from the MAF all the way through the intake plumbing to the TB. Digging deeper into the motor on Friday I found that I'd mistakenly miscounted the chain rollers between the cams when putting the new chain tensioner in place, having 15 instead of 16. I corrected that, installed a new O2 sensor because the old one was original from the donor Passat and white as a ghost, buttoned it back up and it ran beautifully; smooth with plenty of power .. for about a day and a half.

Coming home from work Sunday afternoon it started stumbling and misfiring, having some times where it would barely get out of it's own way. After not running/cooling down for a few minutes (while I looked for problems) it would start and run fine for 3-5 minutes bore stumbling & falling on it's face again. Swapping in the spare ICM for testing didn't change anything so I put the new/old one back in (it's less than a month old). At this point I was getting TB malfunction errors in VCDS so I stopped on the limp home to pick up a spare used TB and an extra set of injectors to send in for rebuilding. Cleaning and installing the TB (and using VCDS for the TBA) seems to have gotten rid of that malfunction error, but the misfires are still there.

I'm really :banghead: with this right now and could stand for any suggestions or ideas.
 

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There are connectors used to transmit the spark signal from coil pack to each plug. If they are still the originals (~18yrs old or more), try replacing the two that look the worst.

These can get flaky when they heat up if they're old.

Also, go through the wiring harness (ECU - ICM and ICM - coils) to look for cracked insulation.
 

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What brand of plugs did you use? For some reason these engines are very demanding of using only the NGK plugs.

Also, any pictures of the installation you would care to share? I seem to remember reading a few years ago on this forum about a guy who was actually working on running a 1.8T backwards so he could install it in a van.
 

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Maybe the AUG and AWM 1,8T's are demanding, but the AEB will run fine on just about any plug of the proper heat range (engine tune dependent) with a solid copper center electrode (gapped to 0.028"). Find some Bosch F6DTCs (a 3 electrode plug) as a starting point. I ran these for 5 yrs (changed every 20K) with no misfire problems.
 

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Discussion Starter · #5 ·
What brand of plugs did you use? For some reason these engines are very demanding of using only the NGK plugs.

Also, any pictures of the installation you would care to share? I seem to remember reading a few years ago on this forum about a guy who was actually working on running a 1.8T backwards so he could install it in a van.
Yeah, that's Andrew of Flint European Automotive in East Nassau, NY. I'm guesstimating there's about a dozen of his reverse-rotation 1.8T's running around with no problems by now, and within the last year he's also got the 06A-type 1.8t running CCW/reverse-rotation. This is being done to allow use of the 5-speed transmission, not just to fit the back of the van .. the engines fit just fine with an adapter but the gearing on the old 4-speed leaves something to be desired. Mine's also running CCW, built by me but in consultation with Andrew, and other than the cam chain roller Rookie Mistake I made and corrected, everything else mechanical -- including the re-indexing of the crankshaft sensor wheel and camshaft sensor wheels needed for CCW operation -- was checked out before I came over here asking dumb questions. :lol: The mechanical stuff is easy for me, it's the computerized engine management that has me on a learning curve; before the donor Passat came along the newest cars I'd owned/worked on were an '89 Cabriolet and an '83 Scirocco, both with 1.8L 8V engines running CIS.

Currently installed plugs are NGK BKUR6ET's, swapped in a couple of weeks ago to replace the NGK BKR6E's I'd installed for the engine rebuild. They helped with the misfire but didn't completely cure it. Two of the coils are new-from-the-store new, but those cylinders are still misfiring. I'll check the wiring and coil connectors the next time I get a chance, which is probably going to be tomorrow evening or Thursday which is my next day off. I've also got a section of harness and set of (4-pin bolt-down) coils from a 2000 Beetle 1.8t sitting on the bench if I need to do an ICM delete modification, but I'd rather not introduce any more variables right now.

What puzzles me is that it was running so beautifully for a day and a half. Boost/vac gauge teed into the FPR hose even got to 15PSI a couple of times...

While it's not done here, this is the closest to a current picture I've got handy right now. I realize the shown intercooler setup is far from ideal but it's a work in progress and will be getting some ducting and a fan ASAP:
Vehicle Auto part Car Engine Automotive exterior
 

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That's cool, thanks! I'm more familiar with the AUG motors, so my advice may not be the best.

Did you try a different ICM? I seem to remember seeing that they have a tendency to fail randomly. In fact, there are people here who have changed the AEB to run on the newer ignition system to eliminate the ICM.
 

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Discussion Starter · #7 ·
Did you try a different ICM? I seem to remember seeing that they have a tendency to fail randomly. In fact, there are people here who have changed the AEB to run on the newer ignition system to eliminate the ICM.
Umm...
Swapping in the spare ICM for testing didn't change anything so I put the new/old one back in (it's less than a month old).
The newer ignition system is the ICM delete I mentioned. I've got the stuff to do it, bought months ago as a "just in case" but I'd rather not go that route unless I have to. Right now I think it'd just be one more variable to contend with.


I've gotta say, in the day and a half that it was running perfectly it was a REAL kick in the pants to drive. Put it in 5th after an interchange, got into the left lane and tromped the gas pedal .. then looked down and saw the speedo needle pegged. It only reads up to 90MPH on this thing but still... :lol:
 

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Sorry, I missed that part of the post. I'm with Electron Man in checking your coil harness. I agree that it's strange it ran well for the day and a half but then suddenly developed and issue. That seems like almost 20 year old electrical gremlins.

Did you do a new oil pump when you did the seals in the motor?
 

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Discussion Starter · #9 ·
New diesel oil pump was installed during the rebuild, OG Passat oil pump pickup tube/screen was cleaned and re-used .. diesel pump, intermediate shaft pump drive gear and cut-down diesel vacuum pump are art of the reverse-rotation configuration. I've got good pressure, showing 100PSI on the gauge at startup and a steady 20PSI at hot idle. Oil is Castrol Edge/Syntec 5w40 with the "big mama" Wix filter. Also a thermostatic sandwich adapter and a plate-style external oil cooler with -8AN lines.

Yeah, it seems electrical to me as well but like I said .. second opinions and insights from people more familiar with these motors is helpful. =)
 

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Discussion Starter · #10 ·
Just as a semi-update, while I won't have a chance to really tear into things until tomorrow I did manage to get a few minutes this evening to look at the ignition wiring. While I didn't see anything obvious, I did clean and re-tighten the ground wire on the valve cover by the #1 coil. It ran smoothly with no misses for several minutes, then more and more misfires started creeping into the counters the longer it ran -- and the more it warmed up. First time I've started the engine since Sunday so it's had plenty of time to cool down...
 

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Do you have good engine grounds? There should be a ground strap nearly the size of the battery cable to the engine block to run all of the electronics the engine has. This is often overlooked in engine swaps.
 

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Discussion Starter · #12 ·
New ground strap at the transaxle nosecone mount and a 2AWG cable from the block to where the battery negative cable bolts to teh body.

I checked and checked and checked for vacuum leaks, but didn't check thoroughly enough. The stupid plastic POS PCV fitting that comes out of the block was split. On the underside where I couldn't see it and where starting fluid couldn't get to it. Huge vacuum leak going into the manifold behind the throttlebody .. except when the turbo spooled up enough to pressurize the manifold and close the check valve at the rubber tee. I also put a set of cleaned-and-flow-matched injectors in, which seems to have helped a bit too.

Off for more test driving. Still a very slight miss at idle but we'll see if it clears up...

Thanks everyone!
 

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Discussion Starter · #14 ·
V8 Ford Explorer radiator stuffed between the frame rails under the floor with a couple of pusher fans on top activated with an old Rabbit fan switch. I've got an aftermarket Jeep-type heater under the dash up front and a combo heat/AC unit under the back seat that doesn't have the AC hooked up yet. Need to find a compressor that doesn't mind running backwards. :rolleyes:

I've been running an ABA/JH hybrid with a KEP adapter on the original Bus transmission with that cooling system for five years and it does just fine, rarely getting much over 210*F on the VDO gauge on grades with temps dropping right back down once the load goes away. Gauge temps correlate with what VCDS reports from the engine's CTS -- 195*F on the gauge and 80*C on the laptop, and they're separate senders so either they're independently both wrong or they're independently both correct.
 

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My Vanagon had an EJ22 in it with an old KEP set-up. In the Vanagon the AEB at 15* sticks up above the floor; in the older buses of course there's plenty of vertical clearance.

To spin the compressor forward, just run the belt on the opposite side of the pulley. Of course, with the AEB belt routing it's no easy feat. You'd need an idler pulley or two and a longer belt, never mind the room.
 

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Discussion Starter · #17 ·
I've been looking at Sanden SD508 compressors because they'll work with either rotation direction, and also at some Denso units from '90s-era Honda's. Up through about '99 or so most Honda 4-cylinders ran CCW rotation.

It's a "someday" project. Every year I think "this summer I'll add A/C to the camper" and every year I don't get around to it. :lol:

Ran it through DEQ (emissions) today and passed with flying colors and no questions asked, so I got my registration stickers. Now to drive the piss out of it. It gets up to 80+MPH waaaay too fast for an old Bus.
 
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