Deciphering Fuel Enrichment Relay Setup

[CriticalB]

Up until yesterday my DeLorean has been running pretty well. At least well enough that I haven't been poking around much lately. One thing my to-do list was get some mufflers installed and have a bung added so I could re-install the O2 sensor. (I discovered after purchasing the old sensor had been cut out of the exhaust and zip-tied to the frame. It's an island twin turbo, and on the way to the muffler shop I know the turbo was working - I could easily hear it spinning up.

They didn't have any mufflers that would fit, but they did weld in a bung with a plug. This quieted things down a bit and on the way home I was listening more to the difference in the exhaust noise than paying attention to the turbos. When I got home I installed the new O2 sensor after the exhaust cooled down. I simply swapped it with the old one and spliced it to the wire running through the frame into the lambda ECU. The first thing I expected to see was the AF gauge next to the boost gauge react, but when that didn't happen, I found it looks like the gauge is wired to power, but the signal wire wasn't connected to anything.

On the way to get some extra wire to hook the AF gauge I realized the turbos were no longer kicking in. In fact, the boost gauge is around -20 at idle, as usual, but under load won't pass 0. Previously it would get to around 3-4 and I'd hear the turbos spin up. I checked all the vacuum hoses, and all the clamps on the the turbo setup and couldn't find any leaks. Well, I did look inside the cubby in the engine bay and found nothing was connected to the carbon canister. I plugged everything back in but it didn't make any difference. I looked all around where the bung was welded and couldn't find anything that would've been disturbed.

Question #1 is: what is happening? If it's a vac leak, why do I still show -20 on the boost gauge?

In researching, I pulled out the turbo install guide looking for anything that might help. I went to check the hobbes switch was connected properly according to the docs and found it was different. Based on the install docs, I expected to find 2 hobbes switches between the ECU and O2 sensor. Instead I have one that's wired up to a relay and the O2 sensor isn't part of the circuit. I have a lot of paperwork passed down from POs and found a diagram and some notes related to a fuel enrichment relay mod - pics attached. The O2 sensor is noted, but I'm not sure from reading this where I'd need to wire it in.

So question #2: How reliable does this setup look - is it worth trying to get back to this, or should I try to get back to the stock setup? How likely is this to have anything to do with loss of turbo functionality since it appears the O2 sensor hasn't been wired in all along.

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[David T]

It was originally done with 2 switches but it is easily done with one and a relay. Doesn't matter as long as you hook it up right. The turbos are operated purely on manifold vacuum. Hooking up the O2 sensor should not have had any effect on boost. Check the hoses to the actuators, maybe they were disturbed when the shop did the bung. The switches and relay are so the A/F meter can use the same O2 sensor and under boost force full enrichment using the WOT circuit. The mufflers are nothing special but if you are going through the trouble of adding mufflers, the later kits used catalytic convertors to reduce the noise and clean up the exhaust. More expensive but cleaner. The muffler is a Walker, I can look up the # if you need it. I can also send you some wiring layouts if you need. Make sure all of the air hoses are in good condition with no leaks and the clamps are all on tight. Verify the timing and advance. Double-check the boost is limited to 5# on both actuators and that they move freely. Good idea to also check the turbo air output for any signs of oil once in a while. Use synthetic oil and change it often. When the Island Turbo kit is working correctly it is a BLAST!

[CriticalB]

That's good to know. So if I leave the relay in, I'll need to wire in the O2 sensor according to the PO's diagram. The only difference seems to be the connection to the ECU / O2 sensor is currently spliced into the Blue/Black wire on the harness for the cold start valve. If I'm reading the factory wiring diagram correctly, that traces back to either the thermo time switch or the hot start relay. So that means the hobbs switch is dictating whether this circuit is active - what sense does that make?

I think the air hoses look good, and I checked the actuators this morning - they seem to be in good shape.

If you could provide that part number for the muffler, I'd really appreciate it. If I were to go with cats rather than mufflers, were those specific to the turbo kit, or would 'stock' cats be sufficient?

I think the air hoses look good, and I checked the actuators this morning - they seem to be in good shape.

[FABombjoy]

A couple of quick things:

The actuators are for the wastegates, which are used to control max pressure. Disconnecting them would only serve to create more boost. I'm thinking the flappers are stuck open and the turbos are being bypassed. You should be able to move them by hand or run 4-6 psi into the actuators and see them move. If you disconnect the arms the flappers should open easily. Google photos of "internal wastegate" for reference as they're almost all the same.

Also, if interested, you can remove the relay entirely from the Island enrichment scheme and use a single hobbs switch that connects ground to the K-Jetronic terminal 11. Same effect without disturbing the O2 sensor wiring.

[NckT]

If it was working fine before, why not just connect the o2 sensor direct to the afr gauge direct and leave the existing method of fuel enrichment intact ? The addition of the oxygen sensor may be trying to lean out the autumnal fueling causing the engine to run not as good as before.

[CriticalB]

A couple of quick things:

The actuators are for the wastegates, which are used to control max pressure. Disconnecting them would only serve to create more boost. I'm thinking the flappers are stuck open and the turbos are being bypassed. You should be able to move them by hand or run 4-6 psi into the actuators and see them move. If you disconnect the arms the flappers should open easily. Google photos of "internal wastegate" for reference as they're almost all the same.

Also, if interested, you can remove the relay entirely from the Island enrichment scheme and use a single hobbs switch that connects ground to the K-Jetronic terminal 11. Same effect without disturbing the O2 sensor wiring.

I disconnected the actuators this morning and the flappers were swinging easily, and the actuators weren't seized. Don't know if they are adjusted correctly, maybe I'll look up how to calibrate them. I suppose it's possible they Got knocked out of whack or something though that seems unlikely.

[CriticalB]

If it was working fine before, why not just connect the o2 sensor direct to the afr gauge direct and leave the existing method of fuel enrichment intact ? The addition of the oxygen sensor may be trying to lean out the autumnal fueling causing the engine to run not as good as before.

Well the goal is definitely to get it working again, but I guess while I'm figuring that out I'm trying to understand why some things I find along the way are different from the norm and whether that's good or bad.

[David T]

It makes no sense that the O2 sensor would get wired into the cold start system. In fact, if you put 12 volts on the O2 sensor you probably can damage it. Or the Lambda ECU. In fact, if you wire it up the wrong way you can damage the Thermo-Time switch. Refer to D:04:15 in your Workshop Manual for tests to make sure the Lambda ECU is functioning correctly by grounding the O2 sensor line, disconnecting it, and applying 1.5 volts to it. I can't tell you if your wiring diagram is good to use until I can see it. Or I can send you one. I will look up the muffler #'s when I get a chance. Refer to D:04:12 for the Lambda wiring and D:04:06 for the cold start system. My guess is the PO was looking for a way to force more fuel into the motor by trying to run the cold start valve. You have some clean-up work to do. First try to get the cold start system and the Lambda system back to stock. Then make sure everything else is OK.

[David T]

I have not been able to find the muffler #. It is a pretty generic one. The approximate dimensions are 8" W X 13" L X 4 1/4" T. The inlet and outlet are 2". The inlet is centered and the outlet is to one side. You must add a hanger so all of the weight is not hanging on the turbo housing. As I said, you should be looking for cats, not mufflers. Might also need exhaust tips to dress up the exhaust. Any exhaust shop should be able to match something up.

[CriticalB]

Thanks for the muffler info, though based on the recommendation I may save up for cats.

I took the cold start valve off the relay circuit and retired everything according to the diagram on my first post. Seemed to be running much better when I took it on a few errands last night. I can easily get to 4-5 lbs of boost. I don't think the turbos quite sound like they used to, but it does feel like power has returned.

There is a basic AF gauge that has been wired to power, but the signal wire was never connected to anything. It always showed one bright green LED at full rich. I clipped it to the O2 sensor and at first thought it wasn't on at all, but it was actually just really dim...barely visible. If you look closely you can see a few LEDs bouncing around on the lean side. I don't think the signal wire would affect brightness of the LEDs, so does anyone think it might just be a faulty guage? Is it possible the system is running really lean? I'm not super concerned about this, but thought I'd mention it in case it might be relevant.

What does concern me is what happened today. I decided to drive about 20 miles to the office. There was a little idle hunting after startup, but after it warmed up it stopped hunting and would idle a little high (1000) at stops. On the way home, same thing with the idle hunting while warming up, but about halfway home it would stall whenever returning to idle. Come to a stop, stall. Shift to neutral while coasting, stall. It would restart easily with a little throttle applied (although it usually starts right up without pumping the gas) but as soon as I released the throttle it would bottom out.

It was a looong drive home in stop and go traffic but I made it, and it actually would hold idle again by the time I reached my neighborhood. Once it cooled a bit, it would start normally and idled fine. I checked vacuum lines, checked microswitch adjustment, wiggled wires, etc. the idle hunting stopped, so I took it around the block and after 2 miles it started stalling at idle again. Made it home but I'm not sure where to look next.