Hello...

I'm about this close to throwing in the towel with my car. 90 740T, recent recipient of an L-block 93 940T's engine, new rear main seal, new CPS, new thermostat, new battery, plugs, oil, oil filter, 5 gallons of premium, and 12 quarts of dex/merc-3. I forgot to install the heat shields that go on the exhaust studs. I sealed the leaking EGR tube that was causing a major intake leak last night in the cold and still have a (less) high idle. Also have slight positive crankcase pressure and some oil seepage from under the cap. The cap may need a new seal.

I took it on the highway for a 60 mile trip home. I didn't push it much and stayed mostly out of the turbo. Coolant and oil were properly full, trans fluid was a little low (planned to buy a quart). I kept it under 70 the whole way, temp gauge didn't twitch and didn't move once warmed, even after shutting it off and letting it heat-soak for 5 minutes.

So, here's the problem. About 5 miles into the trip, I hit stop and go 15-50mph traffic. At 15 miles in, I was idling along and the car started missing severely. It was intermittent. The tach would twitch down and the vacuum/turbo gauge twitched towards low vacuum. No engine codes recorded, and no problems like this happened with it parked or test run a few miles.
This did happen before when the old engine was hot. I attributed it to the blown head gasket and the engine generally being shot to bits.
When it started, I wasn't sure it was happening. Pulled over to check and loosen the kick-down cable and washed my hands. I shut it off when I washed my hands. Got back on the freeway heading for my other car and limped it the whole way, heat on full blast and hood cracked. The farther into the trip, and the warmer everything under the hood got, the more frequent the stumbling/missing was. It even started happening under part load and persisted until I was accelerating.

The possible causes I can think of are the power stage amplifier, the RSR/Fuel relay, and the lack of heat shield letting a lot of radiant heat from the turbo hit the head and overheat it. But I doubt the heat shield is that important.

There was also a strange intermittent clicking like a fuel injector or cold-start solenoid clicking, or something deep in the engine ticking 1-5 times in 10 seconds. It varied in frequency and disappeared once the engine was no longer cold, but long before it was fully warm.

The distributor cap, rotor, and wires are all old and due to be replaced. I haven't checked the timing on the new car, but it doesn't seem to run strangely at all except that it was hiccuping when I started/stopped the engine repeatedly to flush the trans fluid. Timing belt is of unknown vintage and is on a list of things to replace.

I'm very close to giving up and selling the thing as is for $1000 and telling the next guy good luck. This brings back nightmare scenarios of a constantly sick car that demands constant attention and is more fragile than any car ever should be. Also, now that I drive it again, I can't believe I drove it with this terrible shimmy and misaligned steering wheel it has since I replaced the tie rods and haven't had it aligned. The seats are also shot, but the majority of the suspension, the brakes, tires, new headliner, repaired sunroof, (much) nicer speakers, memories, and turbo-power are good things.
After spending only 45 minutes today to replace the 240's torque rod bushings and with the simplicity of the B23/M46/LH2.2 (2.0?) on the 84 240, I'm considering dumping the 740, which was my very first car. The 240 also hasn't needed a darn thing done to it to keep it running the same since I got it roadworthy except for an oil-change.

Anyway, sorry about the rant. I'm moving 400 miles north early next week and need a reliable, running car. The 240 is a better option at this point. This engine swap has been a long time coming and it's infuriating to see it fail after all this work.

Hope your bricks are better than mine...
If anyone can think of a good place for me to start, I'd appreciate it. I think a few junkyard relays and power stages is the first thing I'll try, along with installing the heat shields.
I whacked my RSR and felt it to see if it was clicking - it wasn't. I also felt and wiggled my power stage. It wasn't hot and neither seemed to affect the running. If the fuel pump relay briefly shut off and came back on, I think the residual pressure would prevent problems from occurring in the brief interval.

EDIT: Also, the car has a 560 (not 561, or is it?) ECU. The fuel pumps run constantly in KP2, which is how the car ran when I got it - except for 2 years when it consistently turned the pumps on only to prime, then off again until cranking. With the old engine, there was a strange, unpredictable miss that would show up every 2-5 seconds with no pattern. It almost had the same pattern as those old 6-stroke engines you might find at a county fair. It's a CA car with EGR and a cold-start sensor. The knock sensor and Mixture temp sensor (ECT) are from the "new" engine. The ECT has consistent resistance as the old sensor at roughly the same temp, I don't think it's bad.
Also, I cleaned the injector grounds and the body grounds, the new battery's posts, the battery cables, and pretty much everything I could reach. There is a hairline crack in the exhaust manifold, but I've been told it's no big deal.



-Will
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1990 740 Turbo, on its way to stock specs, maybe beyond