So car ran great before. I’m pretty much stock minus intake downpipe and exhaust and an apexi pfc.

I took out injectors and sent them to go get cleaned. Put them back in today and reconnected the UIM. I went to start the car and it immediately climbs to 5k rpm. It might climb even higher but I shut the car off to prevent damage. Are the injectors stuck open? I’m lost here. I don’t think I connected anything wrong or differently than when I took it off. Not my first time I took it off either.

 

Update for anyone with similar issues:

I fixed it. One of my harness wires got squished under the UIM causing a vac leak. I moved that out of the way and retightened and no longer having that issue

 

Not sure why that would cause the RPM to shoot up.

Maybe someone could explain.

Perhaps keep your eye on it. Maybe a sticky throttle cable?

Must have made a lot of noise though, that can be scary enough.

 

An engine vacuum leak will act like a throttle that doesn't fully close: it allows extra air into the intake. The MAP sensor reports the intake air and the ECU fires the injectors accordingly.

 

So the ecu can bypass the TPS signal to it?

The TPS would be telling the ecu that the throttle is closed.

 

Maybe since the start-up fuel mixture is so rich, the engine doesn't run lean with a large vacuum leak and nearly-closed throttle and can rev that high w/o missing.

 

It's counter-intuitive, but the ECU (or even a carbureter) does not use the throttle position to set the amount of fuel.
For an aftermarket ECU, look at the tables for the tune: the rows & columns are the MAP & RPM to lookup the value for fuel. (And a similar lookup table is used for spark timing.)

The TPS value can be used to temporarily tweak the fuel -- like a carb's "accelerator pump", or for an off-throttle fuel cut.

 

You would think there would be some failsafe to prevent the engine from overrevving in the event of a sudden vacuum leak, such as the power brake booster vacuum hose blowing off.

 

dude its from the 80's, more revs are better, always

 

Here is my car fired up with the ISC completely removed. Despite such a massive air leak, something prevented the engine from running amok, loud, but not amok.

 

First, your video is set as Private which means none of us can see it. Try viewing your link from a private window or logging out of youtube to see what we see.


Second, every engine has a window of 'enough fuel' to mix with the amount of air and make power. For instance, at about 3000 RPM my RX7's engine might make best power around 12:1 AFR or 13:1 AFR (12:1 air-to-fuel ratio or 13:1 air-to-fuel ratio) and it has run with the fuel mixture as rich as 10.0 AFR (10:1 air-to-fuel ratio, which is quite rich) and as lean as 17.0 AFR (17:1 air-to-fuel ratio, which is quite lean). It won't make maximum power when the mixture is too rich or too lean, but it will still run when the mixture is close enough that the spark plug can light the mixture and there is enough fuel in the combustion chamber to continue burning. I would expect most engines to stumble or not even run when the mixture is richer (more fuel) than 9.0 AFR or leaner (less fuel) than 18.0 AFR on gasoline.

So my guess is Xion has just the right air leak that the fuel mixture was still close enough to run and accelerate to 5000 RPM, and your engine had too much of an air leak (or not enough fuel for some other reason) for the engine to run.

I wouldn't try to make vacuum leaks happen on purpose, but if you have a standalone ECU and wideband O2 sensor you can try adjusting the mixture to see for yourself how the engine acts. Be careful to only adjust the light load sections and try not to spend a lot of time intentionally running the wrong fuel mixture because it can make extra heat or foul spark plugs.

 

https://www.rx7club.com/3rd-generati...ncing-1147118/

Idle is set by how much air is going into the engine through the throttle body. If you open up a big hole post-throttle body (like squishing a wiring harness making a huge vacuum leak) you get a high idle.

Glad you found the issue!

Dale

 

Thought I set it to unlisted. Here is another try.

Xion fear, I think, was that the car would just keep revving higher, so he shut the motor off at 5000. But your saying that the eventually the motor would have stalled out.

Our theory, right or wrong, was that somehow we needed to overcome the flooding, by adding excess air. (until it fired and held).

 

Off topic but man I want that fender/front end cover in the video for working on the cars............

 

I will try to look up where I got it. From guys that make replacement seat covers. Tried to get them to make an actual '99 spec bra.But no go.