Won't accelerate past 1,500rpm

[Michael540]

The car has recently gotten a new and rebuilt cylinder head, after trying to start it for the first time it turned on with a really lumpy idle, barely stays on without having to accelerate it. Sometimes it just doesn't wanna start at all. But the biggest concern for me is that it doesn't want to accelerate past 1,500 to 2,000rpm. It just starts making this up and down noise (kind of like a whooing noise) like it were being electronically limited to not go any higher. And if i rev it suddenly it sounds like it's getting flooded with fuel. Please any ideas and suggestions will help, I'm on the brink of having my car running again since last year and i can't wait to be able to drive it.

[Brianmoooore]

Some idea of what engine you have would help!

[Michael540]

I Apologize, it's an 2.5L M20 engine from a 1990 325i.

[Brianmoooore]

Plug leads in correct order?

[Michael540]

Yep, car was actually starting up pretty normally without much difficulty at first but then i started tinker around with the flowmeter air entry/idle bolt, throttle adjustment bolt and i made things worse because the idle rougher now and it refused to start the last attempts i tried to start it.

[Speedtouch]

Are you sure the cambelt is correctly fitted? If it's a tooth or two out, this can cause such issues.

[Brianmoooore]

i started tinker around with the flowmeter air entry/idle bolt, throttle adjustment bolt

WHY DO PEOPLE DO THIS!!!? Why would you move adjustments that only have one correct position, and that is the one they were set at the factory?? Even if moving them did make improvements, all you would be doing is introducing a second fault that happens to counteract the original fault to a degree, and ensuring that even if the original fault is sorted, or 'just goes away', the car still will not run as it should.

There is a round 6 pin plug and socket, fixed to the black metalwork under the inlet manifold, connecting the injector loom to the main engine loom. A design fault allows water to collect inside the rubber boot of the lower half of this connector, corroding the wires inside. Take it apart and check.
Also, the worsening of your symptoms may be as a result of the spark plugs fouling, so take them out and examine them. If any are in a significantly different condition to the others, note where it came from.

[Michael540]

Hey I'm just trying all the alternatives i can find to learn how my car reacts and to fix it. Checked the 6 pin plug, thing looks brand new. Spark plugs are brand new. Gonna reiterate just if i hadn't said this before so maybe it helps more with the diagnosis.


Main problem: engine running rich at any given moment, revs don't get limited, i was even able to test drive the car with the only problem being too rich (icv disconnected), doesn't rev past 2k rpm with icv connected (as if were electronically limited).

With a functioning ICV, improves acceleration but problem remains.


Symptoms:

·Blue smoke & coolant smell after various start attempts while on operating temperature.
·ICV closed shut (worsens throttle response)

Conclusions:
·New ICV doesn't fix problem, helps with throttle response.
·As soon as ECU gets a reading of ICV, engine cuts power when accelerating.

·If you disconnect the ICV you won't get proper air/fuel ratio resulting in running rich. When you connect the ICV, you get proper air\fuel ratio but electronic limitation. The problem isn't the rich running, the problem is the electronic limitation.

[boiliebasher]

Yeah I would just go back and try and undo what you did to make it behave like this.

[boiliebasher]

Essentially check and double check are the work you have done on the car recently. You said it was running fine before so there is no reason why it's cant do the same again.

[Brianmoooore]

It's fine trying to learn about how engines work, but best saved for one that's working properly in the first place, and seeing the effect of things on that, one at a time, and carefully resetting to normal every time.
Even if the plugs are new, they'll still give valuable data, even if the engine has only run a few minutes on them.
I'm a bit confused by what you're saying about the ICV. Idle control valve doesn't send any signal to the ECU (it's the other way around), and in any case, the ICV has no influence on mixture strength. That is controlled by the AFM, the coolant temperature sensor, and, to a smaller amount, the inlet air temp. sensor.
One thing you could try is to disconnect the plug from the engine ECU and measure the resistance between pin 45 of the plug and a good body earth.
Reconnect the ECU, run the engine up to full working temperature, then immediately disconnect the plug and measure the resistance again.

[Michael540]

Whenever i connect the ICV plug back to the ICV the car's revs don't go past 2k rpm. It just keeps bouncing there like i were going on and off the throttle. When i take the plug off the car revs freely.

[Brianmoooore]

The revs bouncing thing I have seen once before, and it was caused by a duff ICV, but I suppose a similar effect would occur if the relevant driver in the ECU had failed.

[Michael540]

What do you mean by the relevant driver in the ECU?

[Michael540]

You think the not wanting to start after on engine warmed up (happens sporadically since it's been able to start a few times) has to do with the whole ICV problem?

[Brianmoooore]

What do you mean by the relevant driver in the ECU?

Probably a couple of FETs that control the current in the two opposing coils in the ICV. I've never had to check in detail.

[Brianmoooore]

You think the not wanting to start after on engine warmed up (happens sporadically since it's been able to start a few times) has to do with the whole ICV problem?

No, I think you have two distinct faults.
See my post of May 6th in this thread.

[Michael540]

"It's fine trying to learn about how engines work, but best saved for one that's working properly in the first place, and seeing the effect of things on that, one at a time, and carefully resetting to normal every time.
Even if the plugs are new, they'll still give valuable data, even if the engine has only run a few minutes on them.
I'm a bit confused by what you're saying about the ICV. Idle control valve doesn't send any signal to the ECU (it's the other way around), and in any case, the ICV has no influence on mixture strength. That is controlled by the AFM, the coolant temperature sensor, and, to a smaller amount, the inlet air temp. sensor.
One thing you could try is to disconnect the plug from the engine ECU and measure the resistance between pin 45 of the plug and a good body earth.
Reconnect the ECU, run the engine up to full working temperature, then immediately disconnect the plug and measure the resistance again."

You mean this?

[Brianmoooore]

Yes, the last two paragraphs.

[Michael540]

I'm sorry but i don't know what I'm suppose to be looking for at this point. I can't find in a diagram what pin 45 does. Why should i be checking that? Sorry if i sound like I'm questioning anybody's knowledge i just wanna know why I'm doing what I'm doing since this goes beyond my knowledge.

[Brianmoooore]

You will be checking that the correct signal from the coolant temperature sensor is being received by the engine ECU.
http://www.autolib.diakom.ru/CAR/BMW/19 ... /fig02.pdf

[Michael540]

Ok i found what it's for (Pin 45): Coolant temperature input. Now is that the blue or the orange/brown plug? Cause right now my thermostat housing has only the blue one connected (the small harness that went with the fuel rail with the blue and orange plug and the other main plug were faulty, the blue and orange plugs were burnt to crisp therefore weren't connected. So i swapped the whole small harness for one in good condition and plugged in just the blue one, the hole for the brown one is non-existent because their is an auxiliary temp gauge fitted in the car). So currently i have the blue plug connected while before i didn't the cylinder head repair i had none of the blue or orange connected.

[Brianmoooore]

The coolant temperature sensor is the blue one. Don't touch it or any of its wiring, other than at the ECU plug as described in my post, until you have measured the two resistance values.

[boiliebasher]

Blue one is the one that feeds ECU. Brown one feeds dash temp gauge. It's all easily found online with a quick search...

[Ukhozi]

after accepting the fact that with your skills set and knowledge you should never have fiddled with it in the first place set everything back to 'factory settings', check all connections that have been disturbed for loose, burnt or broken wires, forget ICV. it is what is says, IDLE control valve and controls IDLE, so nothing to do with 2k RPM. Limited RPM is an electronic fault so concentrate on things that might control fuel flow and air flow like the air flow meter, I know plenty of people who tinker with the settings of the flap and bugger it up and takes ages to find the correct setting again. Don't over think the problem, There are so many variables, even on my "simple" '87 M20B20 it took ages to get kick down and acceleration setting right, and I have been a mechanic since 1963-

[Michael540]

I really appreciate the help and advice guys, I'll let you guys know on further work done with the car to fix the problem and maybe even more (still haven't forgotten about the pictures that were asked for).

[Brianmoooore]

The coolant temperature sensor is the blue one. Don't touch it or any of its wiring, other than at the ECU plug as described in my post, until you have measured the two resistance values.