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1990 Chevy S10 2.5, bog problem, Need Help


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#1 mustang8pt

 
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Posted 12 March 2003 - 01:59 PM

Hello everyone,
I just found this great site and was hoping some of you experts could give me a hand.
I'm having a problem with a friends pickup truck. It's really a 90 GMC Sonoma, but it's the same as a S10 and everytime I get parts they never have a good listing on the Sonoma so I always tell them it's an S10.
Anyway, here's my problem.
After this truck warms up it has no throttle response in the upper rpm's. The truck will idle but when you give it gas to go it just bogs down and falls on it's face. If you race the crap out of it, it will eventually go. This truck has about 110,000 miles on it. I did a full tune up six months prior and it was running great. Now after this problem started I tried to retrieve a code without any success. The check engine light would come on but it would go back off and not store a code. I used an auto x-ray to try and get the codes. Having no idea what the problem was I started with the little things. First I changed the O2 sensor and then the TPS sensor (TPS is set properly). This didn't fix my problem. I had the owner of the truck run it out of gas and then refuel it, just in case it was a bad fuel issue. He refueled and the problem was still there. I changed the Fuel filter again just in case. I then checked again for codes and got a Code 42 which put me towards the Electronic Spark Timing. The book said it could be the module so I decided on a rebuilt Distributor so I would get a new module and pickup. I also changed out the coil. Well, my problem is still here. I jumped out pins A&B on the Diag plug so I could set the timing to 8 Degress as required. When the jumper is out of the diag plug I have 35 degrees advanced timing according to my timing light. Is this normal? Also, when I drive the truck it's pinging like crazy when you try to give it gas. I was reading a little more and it says that the ECM controls the spark timing along with the Distributor. Well, since I already changed the Dist, could this be an ECM problem? Are the computers know to go bad in these 2.5 4cyl pickups? Are there any common problems I should know of? Are there any other common sensors that control this that may have gone bad?
I need your help. I've just about given up.
Thanks for any help you can give me.
Mike

#2 Guest_Badhammer_*

 
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Posted 12 March 2003 - 05:22 PM

Mike, 35 degrees of advance at idle seems a little high I personally have never seen it higher than 26 degrees. first thing has the truck had any major repairs like the tranmission out of the truck if so check for a loose or missing ground wire on the bellhousing or on the back of the cylinder head if the grounds are ok, it may be a bad ECM we had lots of problems with ECM's years ago. I will check into your problem tomorrow and get back with you.

#3 mustang8pt

 
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Posted 13 March 2003 - 02:18 PM

Badhammer,

Thanks for the info so far and I'll be looking forward to seeing what else you might come up with today.
Thanks
Mike

#4 John John

 
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Posted 13 March 2003 - 04:25 PM

mustang,

Use a Tech 1 and see what the engine temp sensor is reading. I seem to remember something back then that the engine thinks that the engine temp sensor messes up and will be reading something like -40.

I could be wrong, but this is a simple check and I could be wrong about which sensor is showing this. Use the Tech 1 to look for some weird temps coming off the sensors. It has been a while since I have seen this. So my old mind isn't what it use to be.

Something about this sounds familiar to me.
John Danner
GM Service Manager
Service Manger Club Staff

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Posted 13 March 2003 - 07:12 PM

Mike I had to get a service manuel sent to me from our other store. I will have it tomorrow . I should have more things for you to check then.

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Posted 14 March 2003 - 05:10 PM

Mike , check the knock sonsor for the Ing timming, it maybe retarding the timming too much due to the spark knock. also the ECM,if all these check out try an Ecm that is most common on older cars and trucks.

#7 mustang8pt

 
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Posted 15 March 2003 - 02:36 PM

John Danner,

I'll check the engine temp and see what it is. About 6 months ago the truck wouldn't start when it was warmed up and the check engine gave me a code for the temp sensor. I replaced the temp sensor at the thermo housing and reset the computer and the truck was fine after that.
Just in case I'll see what the temp is anyway. Thanks for the help.
Mike

#8 mustang8pt

 
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Posted 15 March 2003 - 02:42 PM

Badhammer,

I did read a little about the knock sensor, but the book I have isn't that great. It says to have a friend hit the manifold while I check the timing to see if it retards the timing when it picks up the hitting of the manifold. Supposed to immitate a knock. Do you know what the reading should be on a voltmeter on the anti knock sensor? I wish it was just another sensor, but for some odd reason and with chevy's past history on computers I'm thinking it's a ECM.
I need to get my hands on a good used one and see what it does.
Thanks for the help,
Mike

Also, any ideas of what the fuel pressure should be on a TBI fuel system? I heard low around 15 psi, but I'm not positive. I don't think this is a fuel related problem but it wouldn't hurt to check it.

#9 Guest_Badhammer_*

 
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Posted 15 March 2003 - 03:25 PM

Tbi fuel injection low pressure is 9 psi max pressure is 13 psi any higher and it will run rich. the knock sensor has a crystal inside it and it produces a varying signal to the ECM and depending on the signal the ECM retards the timmimg enough to control the knock.




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