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Discussion Starter #1
;) Hi everybody

I have this little problem with my 88 c4,when it hits normal temp it feels like it loosing power.the car feels like it has alot more ower when its cold.could it be a cold start valve that doesnt work proberly?I got new plugs-maf-tps-injectors-fuel pump.the motor uses no oil and works really fine.hope to hear from one of you guys..Bongo Denmark
 

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How many miles on the car? Are there any codes set (i.e. check engine light on)?
 

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When the car is cold it is running in open loop mode and uses the MEMCAL chip in the computer which has preprogrammed settings in it and the computer does not use the sensors for adjustment. So your problem probably lies in closed loop mode.Once the oxygen sensor and coolant sensor gets to operating temperature, the computer goes into closed loop mode. When this happens, it switches to the PROM chip and starts taking readings from the sensors to make adjustments to the air/fuel mixture and timing. So you could very possibly have problems with the PROM itself or one of the sensors it is taking the readings from. Probably will need a scan tool for this one.
 

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Patrick maybe on to something. I didn't think about that this time. Could be a good possability.
 

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Discussion Starter #7
Patrick maybe on to something. I didn't think about that this time. Could be a good possability.
thank you guys for helping me out, i removed my cath.conv. long ago,so i think ill go for the scantool,and see if i can find a faulty sensor.What about the cold start valve,if it keeps bringing gas,when it runs in closed loop?then the mixture will be uneven...
 

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Your catalytic converters are clogged. Your car can't exhale. :thumbsup:
That's why I asked the questions I did.:thumbsup:

thank you guys for helping me out, i removed my cath.conv. long ago,so i think ill go for the scantool,and see if i can find a faulty sensor.What about the cold start valve,if it keeps bringing gas,when it runs in closed loop?then the mixture will be uneven...
I'm not sure if the cold start valve should throw a code or not, so it may be a possibility. When you removed your cat conv, what (if anything) did you do to your O2 sensors?

My initial thought was clogged cat or failing O2 sensor. I know O2 sensors usually throw codes, but my '86 didn't when it just started to go bad. A scan tool will help you narrow things down a bit.
 

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Discussion Starter #9
That's why I asked the questions I did.:thumbsup:



I'm not sure if the cold start valve should throw a code or not, so it may be a possibility. When you removed your cat conv, what (if anything) did you do to your O2 sensors?

My initial thought was clogged cat or failing O2 sensor. I know O2 sensors usually throw codes, but my '86 didn't when it just started to go bad. A scan tool will help you narrow things down a bit.
ill try the scantool to see if the 02 sensor or anything else gone bad,i did put a new sensor in 2 years ago,but this doesnt mean that it actually works.thanks everybody.....
 

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Jesper,

There is no cold start valve on an 84. On start-up, you are in Open Loop which, just for clarification, means that the ECM is using the VE tables with O/L modifiers but no fuel trim or other Integrator and Gain controls invoked. That will happen once the O2 sensor is hot enough and ECM goes into Closed Loop. I'm not sure what you mean by "the motor losing power" once it warms up. At what temp does that seem to be occurring and what symptoms are you experiencing? Does it develop a miss? Was it okay before and now it isn't? Need a bit more info.
 

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Discussion Starter #11
Jesper,

There is no cold start valve on an 84. On start-up, you are in Open Loop which, just for clarification, means that the ECM is using the VE tables with O/L modifiers but no fuel trim or other Integrator and Gain controls invoked. That will happen once the O2 sensor is hot enough and ECM goes into Closed Loop. I'm not sure what you mean by "the motor losing power" once it warms up. At what temp does that seem to be occurring and what symptoms are you experiencing? Does it develop a miss? Was it okay before and now it isn't? Need a bit more info.
after 20-30 minutes of driving around town it feels like its loosing around 15-20 hp,engine temp 80 gr celcius(normal temp)it doesnt feel like its at a certain temp.it doesnt develop a miss at all(it did before i change the maf sensor)the car has allways done like this but i have had lot of other things wrong with the car,so now im finally down to this thing.
 

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jesper,

It could be that after 20-30 minutes the manifold is finally heat soaked and some of the fuel is vaporizing. Have you checked to see if fuel pressure remains constant? I would try driving it around and looking at the injectors once it starts to feel like its lost power.
 

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I still got this problem.......everything in the engine is fine i had a tester on it,and a shop who knows what they are doing.i am now thinking....could it be my transmission(converter) that works different(bad) when the car has been driven for half an hour.....just a thought.thanks:lookinup:
 
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