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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: Skunksmash on May 05, 2009, 02:37:54 am
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On my '87 5.7L 2wd auto, (TBi) the engine seems to run very rough on startup. It feels as if there is just a very bad misfire. But once it gets warmed up, ir runs great. No misfire feeling of any kind. Feels solid and smooth. The trucks odometer says 45k, but as we all know that could be 145k, or 245k. Point is i realize the motor is likely pretty old and it is going to be like that, as that is just something old engines will do. Heck new engines will do it so some small extent. But i would like to find the root of the problem and try to weed it out if i could. What do yall think could be done? I have heard that installing a self heating oxygen sensor can help, but i have only heard of this once and have no one else's opinion to go on. Thoughts? Ideas? Opinions?
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When you say at start up do you mean just on a cold start up or a warm start up?
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it might be the coolant temp sensor. To test the coolant sensor, unplug the wire connector and test the resistance across the two terminals of the SENSOR with an ohm meter.
The sensor screws into the intake manifold, on the front passenger side, by the thermostat housing.
Coolant sensor approximate resistance specifications:
177 ohms @ 212 deg. F. or 100 deg. C.
241 ohms @ 194 deg. F. or 90 deg. C.
332 ohms @ 176 deg. F. or 80 deg. C.
467 ohms @ 158 deg. F. or 70 deg. C.
667 ohms @ 140 deg. F. or 60 deg. C.
973 ohms @ 122 deg. F. or 50 deg. C.
1188 ohms @ 113 deg. F. or45 deg. C.
1459 ohms @ 104 deg. F. or 40 deg. C.
1802 ohms @ 95 deg. F. or 35 deg. C.
2238 ohms @ 86 deg. F. or 30 deg. C.
2796 ohms @ 77 deg. F. or 25 deg. C.
3520 ohms @ 68 deg. F. or 20 deg. C.
4450 ohms @ 59 deg. F. or 15 deg. C.
5670 ohms @ 50 deg. F. or 10 deg. C.
7280 ohms @ 41 deg. F. or 5 deg. C.
9420 ohms @ 32 deg. F. or 0 deg. C.
12300 ohms @ 23 deg. F. or -5 deg. C.
16180 ohms @ 14 deg. F. or -10 deg. C.
21450 ohms @ 5 deg. F. or -15 deg. C.
28680 ohms @ -4 deg. F. or -20 deg. C.
52700 ohms @ -22 deg. F. or -30 deg. C.
100700 ohms @ -40 deg. F. or - 40 deg. C.
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Yeah sorry i meant cold starts only. If i do a warm start it runs fine. So i guess you could call it cold blooded. Anyway that is a good idea, i will try that. However, There would seem to be 2 of these little sensors on my truck. One is in the intake as you said, but there is another one in the cylinder head. Well, it looks like there are two lol. Im not really sure what that other one is, but i took it out and it looks just like the other one.
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the one in the head is for the dash the one in the intake is for the ecm
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Well i went ahead and checked it out and they did seem to be a little off. So i went ahead and replaced them both. Not a big deal they were not that expensive. But it did not really do a whole lot to fix the problem. Any other ideas on how i could get rid of my rough cold starts?
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Unplug the vacuum hose from the egr valve to verify it's not being opened. Check for vacuum leaks at the base of the tbi unit. Check your map sensor voltage at idle.
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Well, the EGR valve's vacuum hose has to stay off, cause when it is on the truck runs real rough all the time. I am guessing i need to get a new EGR valve? I dont think you can simply clean the old one. They are like a hundred bucks that is why i have been putting it off.
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when you took off the hose you did plug it right. how long b4 the rough idle and you taking the hose off
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That means your egr solenoid is stuck open. You need an EGR solenoid not an EGR valve. You may want to take the valve off and clean it.
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I agree with Vile it is not the EGR but the EGR solenoid. As far as the rough start I think you will be looking more towards a fuel issue than EGR. Pump, filter or ECM could be at fault with the pump being most suspected.
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Yeah after i posted that i was thinking, if it runs smoother after unplugging the vacuum line to the EGR valve, it cant be the valve it has to be something before it. Cause it is sucking through the valve, and if i plugged it back in, i would be plugging it into something that it could not suck through. I think...
Anyway the fuel filter is new, i did a full and complete tune up when i bought the truck. As for the ECM... do you mean the vehicle's main computer? On my stang it was a separate little chip under the air cleaner. Also maybe installing a fuel pressure regulator might help? Anyway here is a link to the two that Orielly's sells... which one is it? I hope its the cheaper one. It asked if it was a K engine code, but im afraid i dont know how to find that out.
http://www.oreillyauto.com/EW3/DisplayTheParts.do?categoryIndex=0&didSearchFor=Egr%20Solenoid
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Yeah by ECM I do mean main computer (Electronic Control Module) or at least the eprom. This not like the TPI or MPI where the pressures are much higher. The pressure on this system is somewhere around 9 psi. The first question to ask really is what code if any are you receiving? If I remember correctly the eprom has nothing to do with the fuel system. If it turns out to be the ECM, eprom or cal-pack I have one you can have. I could even send you a fuel pump that ran great as of last week but in reality dropping the tank or removing the bed is enough work that a new pump would be a better bet. The module on the ford is for ignition only.
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Yeah i was thinking ICM, or ignition control module. They sold a special tool to get it out. :D
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Yep or grind down the sides of a socket ;) Incidently I also have the EGR solenoid that was also working great and if you want it you can have it.
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Your ecm has a memcal which is a prom not an eprom. It contains the information lookup tables for fuel management, spark timing and executible commands. In order to change the events you would need to replace the prom. Your problem isn't the ecm.
Go through your basic tune up stuff, correct your egr problem, check for vacuum leaks and check the map voltage. Report back after you perform these checks otherwise everyone is guessing for you.
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Well in order to be able to do that i need to know how to figure out if i have a K engine code or not. Anyone here know how? Of course i bought the truck used and as such the owner's manual is long gone.
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What's the 8th digit of your vin?
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Well the 8th number of the vin is in fact... a K. What is that supposed to mean anyway? I guess certain letters are more desirable than others? ???
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The 8th digit is the engine code. 10th digit is model year etc..
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Were there two different 5.7L's that year? Otherwise they would not need to know the engine code, i would just tell the parts store that it was a 5.7L and not a 5.0L. Here are some pics of broke or missing vacuum lines on the truck. I am not sure what exactly they go to, or what they are called. Im not to familiar with all this emissions, stuff, im afraid.
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It goes to the egr solenoid.
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Hey it might be why the EGR solenoid isn't working. ;)
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No it ended up going down to the cancerous growth of emissions crap that runs along the left side of the motor. Got that part fixed. But i went ahead and pulled the solenoid so i can take some pics and ask some more questions. For this next question i will probly need someone familiar with stock TBI stuff. On the side that just one vacuum line plugs into, i dont need any help. I know what line plugs into that. It's the side that has two that i have no idea what to plug in. The one that goes to the EGR valve was plugged into the top, but i have no idea if that was the correct spot. And the bottom one just did not have anything plugged into it at all. Can anyone fill me in on where everything is supposed to go? Below are some pics of the inlets/outlets that i am unsure of. Click 'em to make em bigger. I noticed that not everyone here posts pics in the same way.
When i first bought the truck, it idled pretty bad and would die sometimes when i came to a stop. I knew this was something simple but I was taking full time classes at that time, and had little time to mess with it myself. That and i just didn't feel like it. So i took it to a mechanic, who seemed to think the EGR valve was bad and left the vacuum line off. Not sure if that's all he did but after that the truck ran like a champ. So i am just going to have to track down the broke link in the chain i guess. :) But preferably not after buying a bunch of uneeded parts. Can't really afford that right now. Im sure everyone here has bought a part or two (or three) and installed them, (for one vehicle or another) only to find out later that something else was the problem.
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In the bottom picture the one on the right is to your vacumn source. The one on the left with the barb goes to the EGR valve. The other one I believe is not used.
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The other one is just supposed to have a filter on it. It's just a breather. Skunk do you have the vacuum hose diagram under your hood on the veci label?
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Here is a pic of it, if it is what i think you are talking about.
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Also i forgot to mention that the truck is idling VERY high right now due to this problem.
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yep just follow that diagram.
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Very high idle is a sign of a vacumn leak.
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I guess by follow it, you mean trace down every line that it shows and see if it has a leak? I will do that today and see what i come up with. Although, what if i do so and the problem remains?
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Well the very high idle is gone, after i checked every vacuum line on that diagram. I went ahead and hooked the EGR valve back up as well. I think this may be what killed the high idle. But, now for the very first time since i have owned the truck, the "Service Engine Soon" light is on. It is located just below the odometer. What do yall think? Replace the EGR valve?
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Well, drove a few more miles, and now even the light is off. And the truck is running fine.
???
I guess it just wanted to be messed with a little bit. I have had plenty of cars like that. Still, just another strange fuel injection problem.