Can a CPS output be dependent on temperature?

[toml]

Still trying to chase down some problems (misfiring when idle and very hard to start when it's cold)... I'm considering the CPS as the main culprit.

If the CPS was faulty in some way, that would explain the misfiring at low RPM and running nicely at 2000+ RPM, but would it completely explain the hard-to-start problems?

I understand that if the engine was cranking slowly that the CPS may be causing issues starting, but my problem goes away when the engine is warm, so it doesn't seem to be a cranking speed related problem. Perhaps it's just a case of the engine able to crank faster when it is warm? (not sure if that's entirely possible, or if it would make enough of a difference to cause the starting problems)

Any thoughts?


Tom

 

[aye mate]

Any diagnostic codes?

 

[IJ.]

Any thoughts?


Tom

mmm Donuts.........

 

[drjonez]

mmm Donuts.........

:icon_bigg :icon_bigg :icon_bigg :1zhelp:

seriously, while i suppose it COULD be a problem, the CPS's output shouldn't be temp dependent.

 

[toml]

Any diagnostic codes?

No codes!

mmm Donuts.........

Surprisingly that's a very constant thought in my mind!

seriously, while i suppose it COULD be a problem, the CPS's output shouldn't be temp dependent.

I wouldn't think so either, but to be honest I'm not sure what else to look at. I've checked all the sensors as per the TSRM, the only thing I haven't checked is the cold start injector (which could cause the starting troubles but not the misfiring).

The idle is rock solid at 650rpm so I'm pretty sure it's not the ISC system. Could the TPS be causing problems like these? Doubtful, in my mind.

I'm going to try and source a replacement CPS around here to see if it helps.

Maybe my AFM is broken? who knows!


Tom

 

[drjonez]

the CSI does jack. i've ran w/o one for yrs....

you'll need to define "hard to start" and "cold"....

does it misfire when warm?

 

[Mr. Y]

Check your CPS clearances according to TSRM. I think, it could be CPS problem (if you have too large gaps there).

 

[toml]

drjonez: Yep, I didn't think it could be the CSI.

"hard to start" = takes two or three times when the engine has been cold for a few hours (about 4 hours seems to be the minimum) to start it. it cranks fine, over and over, but just won't start. Once it does start, it sputters for a couple of seconds then raises up to 650rpm idle. If I push the accelerator when it's sputtering, the car will very nearly die.
If the engine has been started in the past couple of hours it starts perfectly, first go.

It misfires when the car is idle. It seems to misfire more when the car is cold, but it still does it when the engine is warm. This is only at idle, the engine runs perfect at higher RPM.

When I increase RPM it seems to hit a bit of a bump at about 1000rpm, feels a little like its going to stall, but after that it revs perfectly.


Mr. Y: I agree with you so I'm going to go check the gaps. I've measured the resistance through the CPS and that is all fine.

 

[Nick M]

Sounds like weak fuel pressure to me. If the one way valve is not working, fuel returns to the tank completely. This is not a lone Supra problem. Many EFI vehicles can have this condition.

As for the misfire, is it only happening when it it is hard to start?

 

[toml]

Sounds like weak fuel pressure to me. If the one way valve is not working, fuel returns to the tank completely. This is not a lone Supra problem. Many EFI vehicles can have this condition.

Sorry, little ignorant here... where abouts is the one way valve?

As for the misfire, is it only happening when it it is hard to start?

No, it misfires always when the car idles.

 

[IJ.]

Tom: It's in the fuel pump.

 

[toml]

Ah, right! Thanks IJ.

 

[drjonez]

yea, i'd check FP and see what that looks like....or maybe a weak FPR.

your "hard starting" could easily be CSI related. w/no CSI you have to crank it a touch longer....some don't mind, some do.

 

[toml]

How is this for a wierd issue:

I went to start the car last night, and as it had been sitting for hours it was hard to start. When it did start up, it stumbled for a couple of seconds and with every stumble the Check Engine Light flashed! Anyone heard of/seen this happen before? What on earth could cause it?

 

[djordan97]

sure if your idle is below 450 rpm it throws a code that says the car isn't running.

 

[toml]

Shouldn't that code stay there? I checked the codes when it was running properly and the only one there was 52 (I have a bad knock sensor)..

 

[bigaaron]

(I have a bad knock sensor)..

Fix it! That's probably the main reason it is running poorly.

 

[Jaguar_5]

I still haven't put together my first 7MGTE yet, let alone driven a working turbo supra, but it surprises me how often this one comes up!!

If i ever get a code 52, i'm not gonna worry about anything else until i get the knock sensor fixed!

 

[drjonez]

Tom, the ECU will do a lamp test on the CEL whenever engine speed falls below 500 rpm.

Knock sensors: What's important to understand about TCCS knock control and where I feel most of the confusion comes from is that some think it's a passive system. They think the sensors just "sit" there waiting for knock to happen. While that's true in a sense what's wrong is thinking knock normally doesn't occur and only happens when there is a problem of some kind.

Nothing could be further from the truth. The knock control system is an active feedback loop. It's the same as the O2 sensor loop in that it's actively controlling an engine parameter. The ECU continually advances timing until it detects the onset of knock and then backs off in increments until the knocking stops. It then begins advancing the timing again. It's doing this all the time. This allows the ESA system to use much more agressive timing than it would if the sensors were passive. In other words your engine is knocking a tiny bit all the time when things are working right. It's operating right on the edge.

This continual pushing of the timing envelope is why the system is monitored and generates codes when something happens to prevent it from working. It's the reason you shouldn't run without knock sensors or when you have a fault in the system. You're not simply operating without a protective function when you do that, you're operating without a normally *active* part of the ESA system.

It's also the reason the ECU retards timing when a knock system fault is detected. It does this to not only protect the engine but to prevent itself from responding to "bad" knock inputs. As long as the fault remains the ECU can't actively push the timing envelope and you will not receive the performance the engine is capable of producing.

So stop thinking of the knock system as passive. It isn't and running without it is akin to running open loop on the O2 sensor, just that different things happen. The bottom line is if you want the engine to run right you must keep the knock sensors and wiring functional.

got some proof that active timing advance is used in the 7M ECU? most modern ECUs do this, but i find it hard to believe the 7M ECU does....

 

[drjonez]

if all your books are modern, then i would have to disagree. everything that i have says that it's a fixed timing table and the KS are just there to remove timing in the event of knock. you have to remember the 7M TCCS was designed in the EARLY '80s, the processing power to do active spark control/advance just wasn't there.