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Question about 1994 Geo Metro ECU/ECM Unit?; Wondering how advanced these are, etc.
Topic Started: Feb 10 2013, 12:45 AM (2,350 Views)
cwatkin


I am still fighting intermittent idling issues with my Metro on cold starts. Mine is a 1994 with the advanced emissions (4 bolts on top of throttle body). Here is what I have been dealing with... Those following here are probably well aware. I have been having an intermittent rough idle on cold starts that is causing the car to sometimes die or just otherwise run crappy. I have done all kinds of work which definitely helped with other issues but this one problem has been going on for a while. I definitely needed a tuneup and the replacement lifters definitely helped. The car can start and run just perfect right off the bat and sometimes it barely wants to start and won't even stay running unless you hold you foot on the gas for a bit. It runs fine with a slight bit of gas and then you let off and it dies. Then, you restart and it runs crappy for a bit. Then, like the flip of a switch, the engine idles perfectly.

One of my friends who used to be a mechanic is suspect of the ECU/ECM. He thinks it is either not getting proper inputs from the various sensors or is intermittently forgetting how to run correctly and when it suddenly relearns how to run, all is well until I shut the car off. I was under the impression that these computers were pretty basic units overall and didn't figure there would be much learning for them to do. I will say that I have been getting various Engine Coolant Temp Sensor check engine lights. I first swapped ECTs between my running engine and a junker to see if that would fix the problem but it didn't help. I then purchased a brand new sensor and it didn't help either. Inspection of the harness revealed no obvious defects where I could see although I am sure there could be a hidden defect somewhere such as under the dash.

I begin wondering about these codes as well as the fact I have poor cold starts. This could definitely be related to the ECT codes 14 and 15 that I have been getting. I don't get them all the time and they are very intermittent. Maybe my ECU/ECM is getting bad information from the ECT which is causing the car to run crappy at times. I could see this being the case if the problem isn't dramatic enough to set a code.

I happened to get an identical 1994 with the same emissions setup at the same time as the car I am driving. The entire car was trash and rusted so I stripped all spare parts off the car, cut up the hulk, and hauled it away for scrap. I kept many parts including the ECM/ECU unit so I am thinking about hooking it up to see what it does for my issue. Since this spare ECM/ECU has been sitting in a box for many months, what type of behavior should I expect when I first hook it up? Will it need to re-learn anything or should it just fire right up and run normal?

Conor



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Woodie
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It will fire up and run EXACTLY as it does now. ECM either works or it is dead. Most likely problem is that you have weak grounds so the ECM and the sensors aren't getting the proper voltage. Disconnect and reconnect every connector you can find. Remove the main sensor ground on the rear of the intake manifold under the throttle body, clean it up with a wire brush, and reconnect it.
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Vkhelldog
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I am still not convinced its not your idle controller, I ended up blocking the vacuum tube from the air cleaner to the idle controller to fix mine, because I failed at the rebuild it with a pin spring that's posted here. Also maybe you should try to trick your iat. No point buying a new iat 20$? When a 1.50$ 750 ohm 1 watt resistor makes it work better.... Other than that, what is the compression, and have you tested your fuel injector and fuel pressure and fuel filter replace? It seems like I asked you most of these questions before but don't recall getting an answer... Good luck I hope you find the cure.
Virgil kellogg.
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geogonfa
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:gp
both above posts have about said it all IMO...the computers either work or their DOA...I would start with the grounds, then the sensors...
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Memphis metro


Vkhelldog
Feb 10 2013, 06:40 AM
Other than that, what is the compression, and have you tested your fuel injector and fuel pressure and fuel filter replace? It seems like I asked you most of these questions before but don't recall getting an answer...
This
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cwatkin


I am looking into my distributor ground now as it looks pretty rough. It looks like some of the wiring is frayed and the connection may not be too solid up where it bolts to the distributor. I am going to upgrade the wire gage as well as get new ends for this.

The grounds on the back of the intake are all bolted to the same location. Is that a bad thing?

What kinds of problems can this cause? Weak spark and poor startup run? Everything else looks fine as far as the tests I ran.

Conor
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cwatkin


I relocated one of the connectors from the single grounding point to two points. This may or may not have helped but we will see when I do a cold start. I completely replaced the distributor ground wire with a #10 and soldered ends on it.

I re-ran the fuel pressure test as Autozone in my town burned down so I was kinda stuck with the gage as they told me it had to be returned to the same store. I could have argued but the new one is about to open so I will return it in a matter of weeks and I felt like retesting some also. Anyway, my pressure at idle is a little over 20psi. There are brief excursions towards 30psi when I hit the gas. Is that normal? The pressure also doesn't bleed down when cold so I take that as a good sign.

I also sprayed carb cleaner around potential vacuum leaks and get no change in the idle so I think that is out.

Conor

Edited by cwatkin, Feb 10 2013, 03:21 PM.
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cwatkin


I also noticed that when I would rev the RPMs up in neutral and let off suddenly, the engine would die completely or almost die and then slowly idle back up to normal. I get the impression that some sensor isn't responding fast enough.

Conor
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cwatkin


I am now very suspect of my TPS. Typed in my symptoms on a search and found they match the signs of a failing TPS on many makes of cars including our Metros...

So, I unplugged the TPS completely and started the car. It had a check engine light but ran better than before!

I am digging out my multimeter and plan to start testing/adjusting the TPS.

Conor
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cwatkin


It looks like all my problems with cold idle may have been related to a TPS (throttle position sensor) that was not adjusted properly. I have adjusted it and I think I am still a little off but things are MUCH improved! I had never messed with this before as Geo Glenn jokingly told me not to mess with this under penalty of death. I guess someone else had it our of adjustment.

Here is what I did.
1. Looked around for directions here how to adjust the TPS here. It looks like there are quite a few different ways depending on your year and model of car.
2. I have the 1994 with the advanced emissions and the idle speed controller (ISC) instead of the IAC like the older models. The directions were different for this.
3. I noticed the directions called for the use of a 3.5mm feeler gage stuck in the throttle stop/lever during the adjustment. I didn't have a 3.5mm gage so I went online and looked up the thickness of coins. A penny and nickel stacked are 3.5mm thick so I used this as my feeler gage. This is probably not perfect but it seemed to work ok....
4. The throttle stop has a screw and looking nut and I do not know if this is set correctly either but I didn't mess with it.
5. I loosened the TPS and moved it until the voltage was 0.99-1.00V on my multimeter and then tightened the screws back down.
6. I fired it up basically cold and the idle was much better and smoother than before but seemed like it was just a tad too fast.
7. I drove the car a while and it did fine.
8. I let it idle when I got back and there was a fast-slow-fast-slow rhythm to the idle. It seemed to be surging on a regular schedule so to speak.
9. I let it idle in 1st gear and noted the same surge in the power every 2-3 seconds or so.

I would say that my situation is greatly improved and I seem to be on the right track but don't have it perfect yet. I called some parts stores while typing this and none have a 3.5mm thick gage of any kind. I guess I can try to stack feeler gage blades in a way to get this thickness. We will see...

Any other suggestions?

Conor
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Vkhelldog
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Your idle will surge until you put the tps back/get it adjusted correctly been there done that... I was in a situation similar to you. My #2 valve was burnt and my idle controller bad... Rebuilt head with stainless steel valves, no blow head gasket recommended by Glenn, plugged vacuum hose off bottom back of air filter, now mine idles perfect and gets 45-55 mpg depending how I drive. I too thought a sensor or tps etc... (Thought to fix cheaply). Now I have two of every sensor and they are all good, including map sensor ). I am trying to help you not make my mistakes... Most mechanic shops will do a free compression test... Stand there and watch if you don't trust them to tell the truth..... And plug off that vacuum hose and see if it helps.... Lol.

I just realized this wasn't true... I did have a bad fuel injector.... So I don't have two good ones of that.... But that's not a sensor either :-). Even with one badly burned valve, another partially burned valve and a bad fuel injector I got 35 mpg... To get 20 you must have a leak? (I think your the guy who said he gets 20 mpg?)
Edited by Vkhelldog, Feb 10 2013, 08:37 PM.
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rjsdotorg
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R E Member

As he said, check your injector also for nice pattern.
Shine a light into the TB and goose the throttle - watch for a nice cone of fuel spray.
Check for vacuum leaks by spraying carb cleaner around hoses and seals.
Also, did you use the jumper in the under hood connector, and check timing?
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cwatkin


I have already checked the injector and cleaned it for good measure just in case. I replaced all vacuum lines due to a few being split early on and sprayed carb cleaner throughout. Everything seems tight. I found the http://geometroforum.com/topic/4829866/1/ and http://geometroforum.com/single/?p=456968&t=4239868 which all indicate I need to use .14" or 3.5mm between the throttle stop. I don't know if mine has been messed with so that is the problem.

It also looks like I may need to reset the ECM between adjustments. Is this right?

Conor
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cwatkin


I wasn't the guy getting 20MPG. That was someone else. Also, I ran a fuel pressure test again today and it holds steady when turned off. The injector is not bleeding down with time.

Conor
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cwatkin


It looks like this problem is mostly solved, if not completely solved. See my post on TPS adjustment at http://geometroforum.com/topic/5068976/1/

Since the throttle body on my currently GOOD engine had been transferred from an oil burning smoker of an engine, it looks like the previous owner had made adjustments to both the throttle stop screw and TPS position to try and compensate for a worn out engine. The reason I had to swap the throttle body and intake from this old engine is due to the fact that my replacement engine came from an older car that was setup differently than mine.

Conor
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