chaseincats

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.

Quick question for you guys. I have changed the fuel injectors, added an in-line check valve between the filter and fuel rail, and changed the fuel pump but I still get a drop in fuel rail pressure overnight. I had a fuel pressure gauge on it and between last night and this morning it went from 36 to 20 psi and will probably be down to 0 within a day or so. Not that this is a problem since with an electric fuel pump the car pressurizes quickly on startup but was just curious where else a check valve could be that might be failing.

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