chaseincats

Hi all, I just put a Dynomax SuperTurbo 17733 on my stock 280 and it is noticeably quieter than the (what turned out to be magnaflow) muffler that was sawed off. I took a look under the car (no cat) and I believe the below is a resonator (correct me if I'm wrong). Do these need to be removed when using the SuperTurbo muffler? The car is almost EV quiet after swapping the magnaflow with this.

Gotcha, so I shouldn't expect the temp to drop if I do that then? Yep, I have the shroud

drops back to operating temp

Heater is good. I do have an aftermarket thermostat installed not OEM Nissan if that matters. The original thermostat I had in there was OEM but the overheating issue also happened with that in there. Next time I drive the car and it heats up I'll raise the idle and see what happens but either way that should test airflow and coolant flow since it would be spinning the pump and fan faster, right?

When this whole thing started I changed the fan clutch, radiator (kept the fan shroud), water pump, thermostat, and used radiator flush so it shouldn't be any of those components...

Update on this. I noticed the car is now only heating up after getting to operating temperature and then driving slowly/idling. Once the car is driving, the temperature drops like a stone which kills my theory about combustion gas in the coolant. They car will puff some white (not blue) smoke when changing gear under WOT so I'm guessing that means the gasket is somewhat compromised in the coolant passages anyway. The car has a brand new Aisin fan clutch which had the same warming-up issue that developed with the old fan clutch which was in good condition anyway. I checked the fan belt's tension and it was good as-is too. Any other ideas?

Update on this. I noticed a few weeks ago that the temp gauge briefly rises when I really hit the pedal and will fall when I drop the idle. That lead me to believe theres combustion gas sneaking into the coolant. Following the directions, I siphoned out a few inches of coolant from the radiator and after about 20 seconds of pumping, the squeeze pump stopped expanding because I was probably pulling coolant into the tester at that point. Because of this, I was unable to do a full 2 minute squeeze test. My question is, can I squeeze the pump until its hard to squeeze, pop it out of the radiator to drop the coolant level back down (now that its no longer under vacuum from the bottle) so I can keep squeezing (as long as I dont squeeze the bulb when I pop it out) or will that contaminate the test? EDIT: I grabbed my transfer pump and sucked enough coolant out of the radiator to fill my overflow bottle (it was about 1/8 full). That gave me more air to pump out of the rad and the color didn't change. My only guess at this point is the leak in the head/head gasket (if that's the issue) is so small that the only time it gets enough gas to heat the car up is when theres more pressure in the cylinders due to higher rpm. I think the plan will be to just drive it until it's bad enough that it heats up at idle and try the test again.

The main efi relay had some resistance so maybe the efi system wasnt getting full power? My main guess is the fuel pump relay had resistance, so maybe it took a little bit longer for power to push its way through the corrosion to turn the pump on? Who knows - all I do know is everyone should test the relays for resistance. The only reason I resurected this old thread was for that PSA haha

I cleaned 2 things - 1) the "teeth" that sit outside of the relay housing (the things that plug into the harness). After cleaning the teeth I took resistance measurements between the circuits. For example (I didn't need to clean this one but it's easy to explain this way) - the fuel pump control relay has 4 teeth. By activating the relay by touching a 9v battery to the left 2 of the 4 teeth the relay will click, I then measured the resistance of the high power circuit (the side which is actuated by the relay itself) 2) if resistance is found (anything over 0.02ish on the multimeter's ohm setting), I opened up the relay by bending the locking prongs back to pull the top of it off. Once open you'll see 2 contacts and rocker looking like this: \ |/ when actuated, the relay arm will shift to \| /. For relays that had resistance, there ALWAYS was some sort of black marks either on the contact side \ / or the relay rocker arm side | Using sandpaper i cleaned them all up and took another measurement confirming there was no more resistance. Top tip: the screw at the bottom of each relay has nothing to do with opening the casing, it screws the relay electrics to the bottom plastic base. Unscrew that screw to pull the articulating arms out of the contacts, it makes it WAY easier to clean both sides that way and screws back in easily.

Long term update. It wasn't the injectors and for the hotter part of the summers that followed, I had the long cold starting issue. A few months back I added a manual switch in the cabin to bypass the Thermotime switch to get the car to start up on crank 1 or 2 regardless of weather which is awesome and works like a charm. That said, I replaced my fuel pump a week or so ago due to it being old as heck and pooping out once. While the car ran great once started, it still had that long cranking issue when it was hot out. I took the relay bracket out and cleaned the teeth of all of them then used a multimeter set to resistance (ohm) and checked the circuits from the teeth and low-and-behold found resistance. I pried open the relays that had resistance (fuel pump and main EFI relay - the fuel pump control relay was fine) and found black corrosion on the relay's rocker arms and tabs they connect to once triggered. After cleaning all of that off, I took another ohm measurement and got basically 0. I put them back in the car a few days later and without using the what I started calling the 'quick start switch' the car roared to life on crank 3. I was absolutely floored. All that to say, take your relay bracket out and take some ohm measurements of the circuits in each relay (after cleaning the teeth with a dremel wire brush or something). If you find anything but "0.02" or below resistance, pry them open and sandpaper off the black corrosion which is no doubt there.

Is there any possibility this is ECU related, and if so how would he test it?

Thanks I'll give this a shot. I have teflon tape laying around so that should do it then.

Was trying to track down a leak and I think I've narrowed it down to oil sneaking out of the threads of the oil pressure sending unit. The unit works great outside of the small leak. Is there an o-ring between it and the block that has gone bad or do they seal to the block in a different way?

Thanks for writing this all up, I'll try and answer them individually No leaks - we've smoked and sprayed it multiple times EFI temp sensor is brand new and in spec Every cylinder is firing spark and fuel (pulled spark plug wires 1 at a time then did the same with the injector power connectors Last time we checked we set it at 10 but even when it was higher as we were setting it the stumble remained The car sounds like its much more similar to your situation since its not bogging/missing it just doesnt want to rev and WILL pop loudly out of the intake if you press the accelerator all the way down and hold it at idle

Normalized meaning the car no longer has a stumble when you hit the accelerator and revs/falls how a normal car should.

Seconding @Ogs Classics's question. My stock 280 has the same cone filter his had and didn't need the stock airbox to run properly. Why would that be necessary for his car?

Moving this over from the "strange intake noise" thread since that's solved. My friend's 1975 280 is having a strange problem where it stumbles every time you hit the gas. We installed an air fuel gauge and when you hit the gas it will go into 'off the chart lean' numbers and then stumble up to catch it. Once it's in a high enough rev range it's responsive, but getting it into the 2.5-3k range is difficult to say the least (see video below). It's also worth noting that it idles fantastically, but it's literally just when you hit the accelerator that the jetronic EFI doesn't throw enough gas at the engine to keep up. The only way to get it to run well(ish) at all is to richen it WAY up using the AFM gear. Another interesting thing is when you pull the plugs they are black but the idle number on the air/fuel ratio gauge says 13.5 when the big gear is set back to the stock tooth (we marked it before messing with it). Mid-13s is the number I have on my '78's afr gauge and my plugs are clean. Here is what we've done so far: Gone through the entire fuel injection bible testing everything it recommends and all values came up properly Cleaned all connections/connectors/grounds according to atlanticz's page Changed EFI temp sensor (it was dead) Change EFI connectors on injectors and temp sensor Cleaned injectors using carb cleaner and a 9v battery to push the cleaner through Put a fuel pressure gauge on it between the filter and rail (36psi) Put a new fuel pressure regulator on it (the old one was hissing, the new one doesn't) Tried a different throttlebody Tried a different AFM (with stock settings) New head & intake manifold gasket (unrelated past problem) Smoke tested the engine for vacuum leaks and capped them all then sprayed the engine with carb cleaner and the idle didn't change indicating we got all the leaks Completed entire 'engine tuneup' chapter of the fsm including timing and valves New fuel filter Here's a video of how it's behaving here - any ideas? My friend is making an account and will take it from here

Thanks, wasn't sure if the colors were just for the links in the 2 pods

Does anyone know the what the amperage is of the EFI relays (the ones in the plastic bracket clip on the battery-side of the relay bracket? This is the fusible link that comes off of the positive terminal of the battery and not the links that are in the 2 pods with the white caps.

Sorry, you're absolutely right - opened the '75 manual for his car and found it there. I'll relay the message thanks Zed

We ended up slightly bending the main metal arm that connects to the circuit board contact which touches the wiper arm's single point towards the top and then we got a reading. The car still stumbles on acceleration however. After all this I just advised my friend to take the car to a shop and be done with it.

My FSM only goes up to page EF48 (1978). Are you looking at a ZX book? Sorry, I meant to say we sanded the wiper contact - we put sand paper between the carbon trace and wiper with the soft side sitting on the carbon.

Ok so while getting that switch sorted helped, we MIGHT have found the final culprit which is the AFM. We went through the below procedure and only got ohm readings on the upper third of the wiper band (upper being where the pedal is more mashed to the floor) on the AFM's circuit board. We even tried pressing the wiper down onto the black/carbon stripe to see if maybe it was bent up and still didn't get any readings from it until the wiper got up into the top third. We sanded the wiper arm contact in case it was corroded but this didn't help. I'm guessing that isn't normal and there should be readings on the multimeter for the duration of travel, correct?: This is page EF-30

If it is the FPR, can those be serviced/cleaned or would I simply need a new one?

Sorry, I forgot about that one - yep it was replaced too.