Thanks for that explanation. I had recalled it moving from 0v to 0.7v but maybe it goes all the way to 1v -- it's been a while since I've generated those graphs.

I'll see if I can get it running today and put the ODBII on it and see what it shows me.

 

Haven't yet kept it running long enough to check the O2 sensor operation yet (but I will). Nor test the y-pipe and cats for blockage.

But, I did replace the throttle body with the vacuum leaky shaft (no impact) and the SAI vacuum "harness" (no impact), as well as all the pulleys and AC clutch (just because I could).

However, the "good news" is that the CEL/ODBII exhibited some new codes and behavior as it was struggling to stay running when cold.

The CEL started blinking this time when I tried to keep it running. I know a blinking CEL has some deeper meaning, but not sure what. That's the first time it's done that.

And in addition to the return of the P0102/P1184 codes (MAF/IAT), it threw three new codes (hurray!): a P0307 (cyl 7 misfire), P0305 (cyl 5 misfire and P0300 (multiiple cyl misfire, presumably 5 and 7).

Finally some codes to confirm that the misfire sounds I've been hearing since this started 9+ weeks ago are real. And that they were occurring on Bank 1 (which is how it sounded).

Thoughts on these codes? Maybe not blocked cats or only the Bank 1 cat? I replaced the coil pack and plugs and inspected the wires and connectors -- but not the wires themselves as they are custom length because I relocated the the coil packs to the front of the engine.

Could it be the injectors or the injector wiring harness the fuel rail (Bank1)? Why would it idle OK once warm but still have a power issue (and not revving over 2,500rpm when under load)?

 

Means that you have CAT damaging misfire. Typically just happens with a dead miss on at least one cylinder.

5 and 7 are on the same bank, if the cat was plugged I would expect 1 and 3 to misfire as well but might be a coincidence. They are adjacent cylinders, hg blow between cylinders do happen but pretty rare and no other signs you have that going on.

Swap wire 5 with similar length wire and see if problem goes to other cylinder.

Plugged injectors would do this, but again that is pretty rare. Saw this on facebook this morning, pretty cool: https://www.facebook.com/marketplace...7961333998879/

 

With the coils relocated to the front right of the engine (a kit I bought on this forum), the (3,) 5 and 7 wires are super long. For some context, the 3 cylinder wire with relocated coils is about 2" longer than the longest wire in a standard NGK wire kit for the D2. I have such a kit that I cannibalize for connectors when I screw one up (so far, only the 3 wire).

The guy who made the kit had a custom wire set made by some company in California I can't recall at the moment, but the part number for the relocated coil wire kits doesn't work any more, so I might have to buy some wire and make one myself.

That injector cleaning tool is super cool, but how do you open the injector? with 12v across it? Never mind, read the whole facebook marketplace posting

 

When I see MAF plus IAT fault codes together, I think there could be a wiring problem at the common ground point, maybe loose or corroded. On the D1, there is a compression crimped splice that is easy to access by opening the big wiring harness crossing the front of the engine for those two sensors (and a couple others, ECT and fuel temp, maybe TPS too). I had to solder mine together to solve intermittent readings on rough roads. Not sure for the D2s, but those two sensors likely have a common ground, just follow the wires back through the harness. Just a hunch, trying to help. The electrical diagrams will show for certain. Might also be two damaged connectors, since they are in the same general area. Does anyone make replacement wiring harnesses?

 

I was thinking the same thing about it being a ground issue, as the code 0102 (and the 1884?) reads as "circuit voltage low", not circuit open.

But I am (finally) going to first carefully inspect the MAF-IAT plug itself carefully (more than just clean off all the dielectric on it; I have a Porsche buddy -- I've got a bunch (7) of those as well, several even run -- who is like a god at fixing connectors "in situ" in a harness).

Regarding ground, you are saying that somewhere along that main harness trunk there is a bundle of ground wires all the equivalent of wire-nutted together somewhere inside the plastic sheath that runs along the firewall? Now that would be typical Lucas, Prince of Darkness, Souihill work (I still love you Anglo Saxons in spite of your "take-something-easy-and-make it-too-clever-by-half-complicated" electrical design philosophy -- is that genetic or learned? Methinks genetic, as I am a quarter English myself and have a tendency to make simple things complicated).

Per JohnZo, does anyone know if this harness ground collection point is the same on the D2 as the D1, i.e., buried in that main trunk of the engine compartment wiring harness?

 

MAF and IAT fault codes together are not related to wiring, the engine gets the IAT from the MAF sensor, that is why they are together. You most likely just have a bad MAF. DIsconnect it as before and chart the 02s.

 

BTW, on the LRD2, started it up yesterday -- takes 3-5 min of carefully feathering the accelerator between 1,500 and 2,000rpm before it will hold idle -- and same backfiring that sound like it is actually happening in the Bank1 manifold (not out the tailpipe) -- and drove it around the ‘hood.

Threw same codes for the MAF/IAT sensor (P0102, P1884) and misfire on 5 and 7 (P0300, P0305, P0307) and no power above 2,200-2,500 rpm (about 50mph) -- it'll stall if you go above that.

Put a vacuum gauge on the brake booster connection on the intake and it pulled 18 inches (45cm), a little low in the 16-22 “good vacuum” range.

I put the temp gun on the cats and got only a 100F difference between the front and back of the cats at idle (600-700rpm).

Bank1 Cat: Front 480F Rear 570F delta 90F
Bank2 Cat: Front 390F Rear 500F delta 110F

Graphed the Cats and they are working properly, and appears the IAT and MAF are as well as they read in a narrow range while at idle. See below.

Based on the above, should I still be going with the cats? Next test I guess would be back pressure? Can I use my vacuum gauge (which is an HFT vacuum/fuel pressure gauge that will read to positive 10psi) on the exhaust or will the heat of the exhaust air fry it? In other words, are exhaust back pressure testing gauges hardened to handle that kind of heat, so I need to buy one of those?

FYI, I can’t find any good used cats at any recyclers (they cut them off now at junkyards as soon as they get the carcass).


Bank1 O2 Sensor 1

Bank2 O2 Sensor 1

ECT, IAT, MAF

 

Never buy used catalytic converters.

 

Ok on the used cats.

At the suggestion of someone earlier, I removed the front O2 sensor on the Bank throwing the misfire codes (Bank1 1357 driver side) under the theory that’s the clogged side so removing the O2 sensor would relieve the back pressure and no effect, i.e., it still doesn’t start or starts with great difficulty.

Would removing the O2 open up the pipe enough to relieve enough back pressure if in fact that is the issue?

Depending on the response, next step might be to purchase a back pressure test kit unless someone has a better recommendation.