Dat73z

This AM some friends wanted to hang out at a local meet so we drove out. My wideband o2 was working most of the time but towards the end it started pegging 10afrs so in the opposite direction from before. I think I need to pull out the entire harness and trace each wire to see what's going on. I initially installed the wideband maybe 7 or 8 yrs or so ago, so it's probably overdue for an inspection. One of my buddies I rolled with was driving a 3.1 Rebello Stroker with triple Mikuni 44s and a 3.9 rear running a bit rich at the transition. On acceleration, the 3.2 turbo at 10psi walks on the 3.1 stroker but man that thing is fast. Off the line he's already gone by the time I'm at full spool but on the freeway the turbo has more legs.

The o2 sensor gauge has been bugging the heck out of me so after lunch I checked out the harness. Everything is crimped/soldered/heatshrunk. I jiggled the whole thing around for a while and didn't find anything loose. Started the car up and the gauge was working again, went for a long drive for errands and worked the entire time. I have no idea what's going on but I guess it works again. I still question the afr values since there was a point when the gauge was intermittently functioning that it would always read high afr values when I knew it was running rich so I'll keep tuning by feel and reading the plugs but at least the afrs give me an idea of the direction for adjustments. 20221015_143242.mp4

For reference here's the Bosch o2 sensor part number. The box looks beat up but the o2 sensor visually looked new. Hopefully someone didn't put a used part in there and do a shady return, I've had that happen before with Autozone/O'Reillys parts.

I cross referenced some part numbers and found a matching wideband o2 sensor at my local autozone. So this AM after dropping my wife off at her appt I picked up the sensor and installed it. The old sensor had some red residue which I wasn't sure if it was rust or fuel additive but it visually did not look carbon fouled at all. So an interesting result after installing the new sensor. Throughout the drive the afrs were reading maybe 1/4 pt lower than what I was seeing before. Including the transition region where sometimes I saw 13afrs was now in the mid high 12s. On the last turn before I got home I was doing some testing and quickly went into boost then back into engine braking. I've been trying to tune this area a bit as I know under certain boost then off boost conditions I will spit fire out the exhaust. The afr gauge then pegged back to 16 and stayed there after the exhaust popping stopped. So I'm back to where I was yesterday. I'm still not sure what's going on but I guess I still don't trust the afr gauge. I'm going to inspect the gauge harness behind the dash and see if I can find anything. 20221015_103954.mp4 20221015_105905.mp4

The o2 sensor was really bugging me so I went for a drive and did a lot of redline pulls with lots of boost. Halfway through the drive the afr gauge started working again and indicated 11-12afrs. Then it started randomly jumping to 16 afrs pegging the lean side of the gauge. I wonder if it's a loose wire or if the o2 sensor is fouled. I think I need to find a way to monitor/log the o2 sensor voltage while I'm driving but I suspect the voltage signal is jumping around. I think I have a used spare o2 sensor somewhere as well.

Managed to get the car up after work this PM. Overall the undercarriage looks good. I couldn't find any signs of exhaust leaks. Everything looks good, and the connector is a locking type. Maybe the next step is to test the inline o2 sensor voltage and see if the o2 sensor itself is bad. Hopefully not because this was one of those parts I waited weeks or months for from the UK earlier this yr due to supply chain delays.

One other thing I'd like to try is downsizing my pump jets from 45 to 40. I have 45, 40, and 35 pump jets to play with. At WOT with the 45s I can sometimes rich stumble the motor for a split second around the transition to the mains. Otherwise the volume is about right for blipping the throttle rev matching downshifts and heel toe. Need a working afr gauge for this as I suspect there is some contribution of fuel being pulled from the accel circuit at high rpms. But generally this is another area I generally tune by feel and response.

@madkaw yeah there was a period of time where I just didn't trust the gauge at all, I was tuning by feel and plug reading. Update on the gauge below again lol. So this morning I went for a hundred mile drive and tried 60 pilots with 1.98mm air orifices. Temps were maybe in the 50s. Vacuum cruise is high 11 and low 12 afrs right before boost threshold. Vacuum engine braking (advance) with the 123 MAP of course leans out the mixture with no load to 13-14afrs for response and economy. The transition is in the 12s and when the mains come on mid 11s to redline. Then my afr gauge pegged 16 and stayed there. I suspect maybe I blew out the o2 sensor or a vband came loose, I'll check it out later today. It was nice just driving and not constantly looking at the gauge. So again another unexpected result, even sizing down the pilots I'm getting the same transition values assuming my gauge is reading correct. The plugs still look good no sign of detonation. Response of course is even better off idle-2k rpms. I also tried some brake boosting and it's a rush but Im getting some boost spikes. Likely I'll need to upsize the vacuum lines from 4 to 6mm and move the MAP closer to the plenum as it's currently behind my dash. Not too worried about the spikes for now as I know the mixture is enrichening along with pulling timing and the motor is fully built. Next steps after fixing the afr gauge is to raise the float level a bit and get into any final checks and tweaks for the dyno. I got through most of my list from a month or so ago, but due to my schedule I'm going to give myself a solid 2 weeks to do some basic maintenance.

Tonight, I compared a 65 pilot jet with ~1.98mm air orifice against a 60 pilot with ~1.32mm air orifice. First impressions are the fuel curves are similar in both. The 65 pilot is more responsive with the larger air, but the 60 pilot seems to have better cruise AFR's and is slightly richer in the transition. Both cruise slightly rich in low 11 AFRs. I think I'll attempt a 60 pilot with ~1.98mm air for response and raise the float level from 28mm to 27mm to tip in the mains sooner and see how that works. What I'm tuning for is the transition region where sometimes I see 13afrs depending on load and gear and of course when you're at freeway cruise and just tipping in with the turbo instantaneously spooling. The reality at this point is unless I had the AFR gauge I don't think I would be trying any of this as the drivability is good and the plugs look ok. So perhaps this is a case of I need to tape over the gauge and stop looking at it.

That looks really good @rossman. Does the car cool at speed? I've seen some ppl louver or cut slots/add rubber flaps to allow the shroud to duct the airflow from the front at standstill and still allow for good air evacuation through the rad at speed

I raised the fuel level last night from 29mm to 28mm, and went for a long drive for errands. The response wasn't as I expected. Actually I didn't really see a response, but maybe I need to do more testing this weekend. At low/no boost I saw a definite trend in the AFR gauge of increasing richness/earlier main onset with higher fuel levels. I'm going to play with the idle jets a bit more next. I read somewhere that, the position, size and diameter of the air orifices on the idle jet should affect the response of the fuel curve similar to the main jet, air and emulsion tube. So basically like a mini main jet stack. At this point I'm just fine tuning around the turbo spool so minor changes to air size/position and 1-to-half sizes on the fuel orifices. I do know my tune has been changing with the weather, and with my life schedule waiting a few days between fine adjustments can show completely different results. The initial jetting was done on 90-107F days, and now I'm driving the car around in 40-50F lower temps. The good thing is I have a solid base tune now to default back to which I'll likely use for the dyno in a couple weeks, so unless there is a definitely improvement in drivability I'd rather err on safety which is more rich and less timing.

Yeah it's one of those things where it's best to leave it alone once you get it "good enough". I've easily spent more time at this point tuning/tinkering than actually doing all of the mechanical stuff earlier in this build thread to make this all work. Blowing through with a turbo adds dimensionality where you're dealing with variable fuel pressure and spool which varies by load, gear and temps.

It's been another busy week so I haven't had much time for this project. But this evening I'm planning to raise the float level from 29mm to 28mm to bring on the mains slightly sooner and play with the idle circuit a bit more. I have some additional jet settings I'd like to try. For reference, earlier this summer when I was tuning NA I tried float levels from 25mm to 29mm down. At 25mm the mains basically come on around 1.5-2k RPMS. That was also with 36mm outer venturis, and I've switched to 38mm OV's to tune through some other issues. At 29mm the mains are on in the 3-4kRPM range. I'd like to mains to come on around 3k RPMS which would allow me to cruise on the pilot circuit, but have the extra fuel available as the turbo fully spools. That is the idea at least.

Tonight I stopped by the store to get the boost leak tester materials. I think I'm about $15 into the parts. Checking out prices at HD and Harbor Freight everything has easily gone up 20-50% over the past few years, I decided to save a few $s and went for the air hose quick disconnect and I'll use the gauge on my regulator to see what psi I'm at. I'll start assembling later tonight if I can find 30 mins or so.

I would start by reading the plugs and inspecting the oil to ensure it isn't a malfunctioning carb issue dumping fuel into the engine, although if that was the case I'd think you would've already fouled out the plugs and have a crankcase full of fuel. I'm not sure what benefit you'd get from the fuel flow gauge, I'd think an afr gauge would be more useful. For what it's worth on a LS1 GTO I think I was averaging like 6-8mpg mostly hooning around town. Never had a carb'd big block but 2-3 might be reasonable?

So I have noticed some tiny dots of what looks like oil on my hot side charge pipe over the past few weeks. It's fairly minor but has been driving me nuts as everything in front and around it is bone dry. Not sure if it's being slung from somewhere else, maybe the crank area and my efans are blowing things around.

@rossman With the cooler weather I have noticed the afr gauge is generally reading a half a pt or so higher across the board going from 90-107F weather which is when I was doing the majority of the jetting to recently dropping into the 50-60s in the AM. The turbo does like the cooler fall weather though, and humidity here is low. I've only lived with EFI turbo cars in the past so this is all new to me. I should probably carry extra jets with me for cool/hot, and high vs sea level elevation lol.

Pulled the plugs again to check and fine tune the mixtures a bit more. Things are looking pretty close to where I had it tuned before machining the mixture screws for orings, but I've noticed the tune changing slightly with the cooler fall weather.

Quick weekend update. Life has been busy but I managed to put another ~hundred miles on the car. I've been trying to drive it for all of the errands to get more shakedown time in. I've noticed the boost response and over boost values are fairly sensitive at certain ranges. Fundamentally I think I'm basically tuning the duty cycle of the boost control solenoid to match my setup. So I'll keep playing with the settings. I'm hoping this AM I can make a trip to Home Depot/Harbor Freight and at least pick up the parts to build the boost leak tester.

After going hard at work for a few months I felt like I was burning out so I decided to take this afternoon off. During my grocery run I was playing with the EVC-S a bit more. One pull felt exceptionally stronger than the rest. Looking at the peak hold function, boost spiked to 16.5psi. So I think I need to tune things out a bit more. Each pull was smooth to 6-7k, no detonation that I could tell at least and AFR's were within 11-12.

Finally almost at the weekend. Got word that my needle and seats are ready, but this weekend is my wife's birthday so we'll see if I can make any progress with the turbo build. If I can find an hour or two, I would like to build a simple tester to boost leak check my system. Also one thing I found interesting: I took the car out to grab a quick lunch yesterday and noticed even with the EVC-S set to wastegate mode I was seeing 10psi, which is my wastegate spring pressure. I thought I had saw a 2psi drop past the butterflies from system losses where my gauge is reading before boost control. So I'm not sure if I'm misremembering, but I guess this is what happens when it takes me months to do some simple boost adjustments. I'm going to start writing things down in a log book and keep it in the car.

@Zetsaz I spent a few weeks investigating the gaps a couple years ago and the conclusion I came to was every 70-73 240z I saw in person (didn't check the 280s) was assembled differently from the factory. My car has maybe a mm difference between the DS and PS rockers, add to that the tolerances of a mm here and here for how the seams in the doors were folded, fenders, etc. and you ended up with a couple mm differences here and there lol Best way to resolve this is probably to line up the rears of the doors first, then add or remove metal to get nice even gaps before paint

I took some measurements on my doors which don't look like they've ever been taken off the car, but my fenders have been shifted around. Also, the way my rockers were welded from the factory are different DS versus PS. The gaps measure 4-7mm, so somewhere between 5-6mm sounds about right.

Did some testing tonight and the HKS boost controller holds consistent boost. With the MBC I was getting random spikes, and sometimes inconsistent peak boost. I really need to check for boost leaks. At WG spring pressure only I was seeing 10psi on the HKS controller. At 25% offset I was expecting to see somewhere around 12psi but I only peaked at 11.2 psi. The solenoid position also seems ok, the valve body is cool enough to touch. But of course at shutdown unless I open the hood everything heat soaks.

Some initial settings to start: Low Boost A Offset: 10% Response Value: 10% Over Boost Value: 3PSI Warning Value: 11PSI Drop Value: 100% In doing some research, the Overboost Value and Response Value for these controllers is critical to get right. Or you get hysteresis in the controls like you see in the chart and can overshoot on boost, will hit the warning but won't drop boost to gate default, or have other issues. It's been many years since I've done control work/design so I'm just going to play with the settings at low boost until I get a good feel for what the settings are doing, and what the turbo likes.