chaseincats

We noticed the water temp switch was unplugged, and when plugged in the car ran way better. He is not using the transistor ignition module, so why would the car run differently with this hooked up as I thought that was only tied to the stock ignition system. Any ideas?

We tried that one already and all the ECU connector tests in the fuel injection bible but everything checks out correctly. We know the AFM is working because if we turn the large gear inside the afm the air fuel gauge’s numbers change, so it is working. We did take the ecu out and it does have some brown dried liquid on it if that means anything. here are some pictures if it helps. I also attached an image of a sensor not on my 78 either just in case that has anything to do with it. It sits on the thermostat mount below the fuel rail.

So we got it running without a hiss and it idles great but when we hit the gas it heavily stumbles and front fires. We have an air fuel gauge on it and it goes off the charts lean the second you hit the pedal but idles in the mid 13s on the gauge. I tested the TPS by unplugging it and the car runs leaner with it unplugged and richer replugged telling me it’s working. The coolant temp sensor is new as are the connectors for it. We put a fuel pressure gauge on it and it’s sitting more-or-less where it should be (36-40psi) idling and with the pedal pressed. Even if that isn’t 100% correct it should be running out of gas as-is. One thing I noticed that’s strange is the car won’t even start with the coolant temp sensor unplugged (before we sealed vacuum leaks it started right up). Not sure if that helps or not though. I made a video which might help: https://youtu.be/bq_ppptWZxI

If leaving the bcdd at the junkyard means the throttlebody is destroyed then i guess so

No but when we held the other on the manifold we just covered the bottom with our palm essentially doing the same thing as the plate...

Thanks for this, we got the idle down to where it should be and the sound is gone. The culprit was indeed the bcdd blockoff plate - had no idea you were supposed to silicone the holes inside the throttlebody shut so air doesn't pass through. These blockoff plates really should come with instructions to give the purchaser a heads up that needs to be done. What was most likely happening is the intake noise was the sound of air whistling through that passageway in the throttlebody and then echoing down the intake piping. This is the image that really made it all click from one of Captain Obvious's threads:

I looked yesterday for bcdd threads with you in it but couldn't find any with sage advice on the process...

Wow that's odd, ok then

Didn't know that - will do. I did remember there is some strange sensor on his engine (75) which isn't on mine (78) and is not plugged in. It sits right next to the fuel rail/thermostat housing and has 2 bullet connectors and has a vacuum port on it - is this part of the coolant temperature system for that earlier 280? I looked online but I can't find any pictures of it or a name...

The TB he's using currently has a bcdd blockoff plate - we also sprayed that badboy with starter fluid and it seems sealed though

Update for you - the pcv valve was fine when he tested it per the fsm but the hose was still split which has since been fixed. The noise is still there but with a new coolant temp sensor and pcv hose, the idle dropped from 2500 to 1300 with the thottlebody screw placed all the way in. Changing topics from the noise to the idle speed, we've found all the vacuum leaks with the car dying at this point when you take the oil cap off. With the idle screw all the way in on the throttlebody, could this be an ecu issue causing it to run so fast? If we pull the temp sensor connector, the car's idle will drop drastically (maybe down to 400 or so) but that's simply because the car is running in max rich mode. Any ideas besides vacuum leaks that could cause such a high idle? There really can't be any leak areas left especially after smoking the engine and using a good chunk of starter fluid blasting the manifold...

I spoke with him and he bought a brand new valve but said he could blow through both sides there too. He read later on that blowing into these doesn't tell you anything, you have to suck on it to get an actual answer of if its bad or not - is that correct?

Update for you guys. The PCV valve even though its a few weeks old very much is letting air in both directions not to mention the pcv hose is apparently split towards the top. He's going to get a replacement valve and snip off the torn portion of the hose. When I hear how it went I'll update you all. Thanks so far

The strange thing is my 78 has the exact same air filter and doesn't make that sound the only difference is I have the weber big-throat throttlebody I believe he has the stock air cleaner so I'll pass the message along to give that a shot though

The sound literally comes through the intake piping all the way to the throttlebody

The problem is the noise is there with the cold air intake removed. It's also there with the afm removed haha.

You hear it especially well when I put the camera right next to the air cleaner. It’s a loud sucking noise much louder than my car. You literally can hear it coming down the street it’s really strange.

We actually did that. Sprayed absolutely everywhere to no avail. I don’t think there are any leaks because the rpms drop drastically with the oil cap off

Intact in what sense? The hose is connected to the block and intake manifold with the new pcv screwed into the intake. Is there anything else I’d be missing? The valve cover hose isn’t plugged either. Oddly the car barely ran without the throttlebody on. I’d have thought the engine would freak out too.

The pcv valve is new but I’ll have him check that

Hi guys, My friend's 75 280 has always made this strange hissing from the intake: https://youtu.be/mjrzNhHvXL4. Any ideas what this could be? We took off the cone filter and when we did we could hear it from the afm, so we took off the afm, and could hear it through the throttlebody, when we took off the throttlebody the sound stopped (kept the engine running by pulling the temp sensor cable and left the tps switch in to run rich enough for it to not die). We've checked multiple times for vacuum leaks using both a smoker and a can of starter fluid on the manifold and there are no leaks. We also tried 2 other throttlebodies and both make that noise. I've never heard if this issue - has anyone encountered it? -chase

That shouldn't be ok though I'd think, right? Guessing it's at least a sign of it needing to be replaced sooner rather than later, no?

Hi guys, I was driving my 78 today and the car died while driving. I pulled over, checked for spark, pulled the oil pressure switch to force the pump on and nothing. I have a manual trigger for the cold start valve and when I did it, the car tried to start but after the fuel rail was cleared of fuel, that trick no longer worked. Eventually, after playing around with it further by pulling the fuel pressure regulator hose it started. I then put everything back the way it was and it continued to run a little rough but smoothed out leading me to believe the stuff I did under the hood didn't change anything. The rest of the trip went fine and it ran great including another hour-home drive. The pump is at least 7 years old (the amount of time I've owned the car) and that could be dying (or dirty) but a strange thing I noticed is during the short trip in which it died (after driving for 45 minutes), the starter sounded different, almost like it was struggling to turn. After the car died, for all subsequent cranks after that, the starter sounded perfectly normal. I know these are two different problems but I'm curious if any of you have any ideas as to why both happened on the same trip (the car died about 3 minutes after that starting cranking issue). The battery is really strong (per the volt gauge) so it shouldn't be that. Any ideas? -chase

Gotcha - thanks all!

Disconnecting the blue wire from the ignition box worked. Should we leave the other wires connected or remove the box in full? All wires except the blue are still connected and the car runs with the tach.