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Still Learning
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Discussion Starter #1
Ok so we just moved from los Angeles to south east Idaho which is about 6000 ft above sea level. I have a 1989 Chevy c3500 with a 350 out of a caprice. It has 2 fuel injectors, each one fires 4 cylinders. I remember it was running a little rich before I left LA but now I can smell straight gas coming out of the exhaust. Is there an adjustment that I need to make for the altitude change? What else could be the problem?
 

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There is less oxygen in the air the higher you go in elevation. I would make sure it has a clean air filter. A K&N oil/gauze air filter would help get more air into the engine.
 

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" Euro " electrician
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Ok so we just moved from los Angeles to south east Idaho which is about 6000 ft above sea level. I have a 1989 Chevy c3500 with a 350 out of a caprice. It has 2 fuel injectors, each one fires 4 cylinders. I remember it was running a little rich before I left LA but now I can smell straight gas coming out of the exhaust. Is there an adjustment that I need to make for the altitude change? What else could be the problem?
The MAP ( manifold asbolute pressure ) sensor can go bad and not reading correct altuide setting and also the O2 sensor as well.

As far for the 350 Caprice engine what year is that and did you transfer all the related emminson hardware from the oringal engine to the caprice engine on that truck ?

That will make the differnce there.

Merci,
Marc
 

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JOATMON
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Check the connection to your temp sending unit.

I have a 93 TBI in my jeep....it's basically the same setup you have.

Wait...what year Caprice? If you have a TBI and not a TPI, then, yes you have 2 injectors but they both pretty much feed all cylinders.

So....assuming you have TBI and it's like my setup....

Your primary sensor are MAP (Manifold Air Pressure), CTS (Coolant Temp Sensor), TPS (Throttle Position Sensor) and your dist (tells the computer what cyl is ready to fire)

In most cases, if your running rich it's because the CTS thinks the engine is colder than it is. About the only real way to know is to hook up a OBDI scanner and look at the reading the computer is getting.

You could also have a bad MAP. You can test that by just measuring the voltage coming out. When you first start the engine, before it actually cranks it measures the voltage...this is basically your altitude reference....after that, the voltage tells the computer how much manifold vacuum you have.

It all comes back to needing a scanner and reading real data to get an idea of what is going on.
 

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Still Learning
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Discussion Starter #5
The MAP ( manifold asbolute pressure ) sensor can go bad and not reading correct altuide setting and also the O2 sensor as well.

As far for the 350 Caprice engine what year is that and did you transfer all the related emminson hardware from the oringal engine to the caprice engine on that truck ?

That will make the differnce there.

Merci,
Marc
The MAP ( manifold asbolute pressure ) sensor can go bad and not reading correct altuide setting and also the O2 sensor as well.

As far for the 350 Caprice engine what year is that and did you transfer all the related emminson hardware from the oringal engine to the caprice engine on that truck ?

That will make the differnce there.

Merci,
Marc
Um... I bought this truck off of some dude and the only information I got about the engine is that it came out of a caprice. I can tell that it is a late 80's model because all of the stuff I been replacing on it. I don't remember what part made me know it was late 80's but nevertheless I do need to change the o2 sensor, I already changed the temp sensor that screws into the top of the block next to the upper radiator hose, and I changed the thermostat. I don't know about the emmissions stuff, all the hoses coming out of the throttlebody are plugged with screws. Where do I locate the MAP sensor? I never heard of that...
 

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JOATMON
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Oh boy....sounds like that 'dude' did a hack job. There should be at 3 hoses in use off the TB. One in the front should go to a solenoid and the to your evap canister.

In the back, the 1/2" line at the base goes to the valve cover and PVC.

Also on the back but up a little is a real small hose that 'should' go to a black module over on the right side. That is your MAP. With out it the engine runs in open loop limp mode.

Look at my jeep build lin in my sig....you will find some pics of my engine. As soon as I get home I can post more pics.
 

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With fuel injection, all the various engine sensors input information to the engine computer. And based on that information, fuel is adjusted...

However those sensors along with the specific engine and the engine computer are all designed to work together - sounds like just the engine was switched?

I would sell it and get a vehicle which has not been modified - save yourself a LOT of trouble!
 

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You realy need to get a scan tool and look at the data stream or just get one of each and start throwing parts at it.

I agree with the others look at the MAP sensor. Sould be mounted on the right side firewall. Check the vacuum hose for splits, cracks proper sealing... and also see if you are getting manifold vacuum. Inspect the electrical connector for corrosion.

Do not run this truck too long or you will damage the cat (s).
 

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But is that MAP sensor the MAP sensor for a "350 out of a caprice"?

(And is the engine computer and its software for a "350 out of a caprice"?)

From year to year sensors change. For example a sensor for one year might have a "voltage" range from 5 volts to 9 volts. The next year the same sensor might have a range from 3 volts to 7 volts. And the engine computer software would be programmed differently for those different sensors.

So when replacing an engine with something different, you should also change the sensors and the engine computer for that engine...
 

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JOATMON
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Billy bob brings up a good point. Hoefully the 'dude' swapped the computer with the engine. For the most part, if the engine was pulled with everything attached, as long as he swapped the computer, all should be good.

If he swapped just the long block....then you need to make sure your truck is set for that block. You can look at the VIN to see what came in it. If it had a 5.7L before, then your good. But if oit had a v6 then you have issues...computer will be wrong.
 

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I have to agree with Ddawg16. Sounds like it is running in "limp Mode". Are there any code stored in the computer? Is the "check engine/service engine soon" light on? Does the light even work? If it is indeed running in that mode then it is running real rich as a default setting. Compound that with the fact that there is no air up where you are the fuel mix error is even compounded further. If the truck is worth it, you could buy an aftermarket fuel injection/engine management system from Holley or Edelbrock and replace the stock GM system
 

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Oh wow one heckva a mess which I have see it more than I really want to recall it.

Basically let me run quick punch list.

Check the MAP sensor as other mention and one of the member posted the photo what it look like and it useally located on the firewall near passenger side on GM trucks ( few will have on right front fender area only on few specfic models so be aware with it )

Second thing what the water tempture it running now it should be 190-195 degress F. that way the computer will sense it and will go in close loop which it will finetune the fuel system to proper mixure. If you used wrong thermosast like 175 or 180 degress F verison the computer will sense the engine still " cold " and will run in open loop which it will cause the fuel/air mixure to run more richer than normal.

Third thing is look at the hood sticker details it should mention what the oringal engine size and I know with C/K 3500 most common will be either 5.7 or 7.4 liter engine.

Do you still have catatic converter(s) on it or it was removed ?

How many miles do this replaced engine have on it now like rough esttame it is now? ( I am not too suprised that the ingition timming / valve timming can be messed up )

Merci,
Marc
 

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JOATMON
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How is the spray pattern on the injectors. I would pull all that junk out of there and just run a carb.
That is pretty bad advice.....I personally will never go back to a carb....I've had a lot less issues since I did the SBC swap into my jeep.
 

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JOATMON
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47 posted a good pic of the MAP.....

This is my engine and if you look where the transmission dip stick goes down, you will see a black square piece of metal...the MAP is mounted on the other side of it....

I would take a better pic...buy my jeep is up at work...

 

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Still Learning
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Discussion Starter #16
Ok so it warmed up into the 20's today so I was able to take a look at my truck. I was able to locate the MAP sensor between the intake manifold and the distributed. It looks like an easy fix. I'm gonna change the o2 sensor and that MAP sensor this week and see what happens. Also I bought those fancy Bosch platinum spark plugs with a lifetime warranty so I'm gonna swap those out cause they are covered with grime. I just changed the thermostat about a month ago but the housing is cracked so I need to get a new one of those... There are 2 vaccume lines coming out of the front of the intake manifold that are plugged with screws, I don't know where they go though... I also need to buy that oval to round rubber thing that goes from the air filter to the left side of the engine compartment but I don't know what its called... I also bought a performance chip on e bay for 10 bucks hopefully that will help my fuel economy... I'm not sure what a cataletic converter even looks like but I know when I got my truck smogged he put n/a next to cataletic converter, but I did pay him to pass it so I don't know if I do have one or not. Are there any other sensors I should change that I don't know about? I changed the temp sensor but that's about it...
 

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Discussion Starter #17
Oh, I know my truck origionally came with a 454. Only like 1% of these trucks had a oem 350. I don't know how many miles are on this 350 but its running great. The fuel injectors are pumping out gas and its not misfiring at all at the engine. But you can see and hear puffs of smoke coming out the exhaust. It's chugging like an old truck but its not the engine. I did however discover an exhaust leak between the exhaust manifold and the other pipe it connects to under the truck. The smoke is actually leaking up into the engine compartment which might be bad cause I'm kissing that piece that connects to the air filter... And I took out the air filter cause it was clogged up and I'm broke til I get paid tomorrow
 

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And when you are buying those replacement sensors, are you telling them it is for a...

1989 Chevy c3500 with a 454?

Or for an [unknown year] caprice with a 350?
 

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" Euro " electrician
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Ok so it warmed up into the 20's today so I was able to take a look at my truck. I was able to locate the MAP sensor between the intake manifold and the distributed. It looks like an easy fix. I'm gonna change the o2 sensor and that MAP sensor this week and see what happens. Also I bought those fancy Bosch platinum spark plugs with a lifetime warranty so I'm gonna swap those out cause they are covered with grime. I just changed the thermostat about a month ago but the housing is cracked so I need to get a new one of those... There are 2 vaccume lines coming out of the front of the intake manifold that are plugged with screws, I don't know where they go though... I also need to buy that oval to round rubber thing that goes from the air filter to the left side of the engine compartment but I don't know what its called... I also bought a performance chip on e bay for 10 bucks hopefully that will help my fuel economy... I'm not sure what a cataletic converter even looks like but I know when I got my truck smogged he put n/a next to cataletic converter, but I did pay him to pass it so I don't know if I do have one or not. Are there any other sensors I should change that I don't know about? I changed the temp sensor but that's about it...
Ok when you plan to change the thermosat make sure you get one that rated for 192-195 degress F verison this is the only way you can get it back in line with computer controller.

For the performace chip that is kinda like touch and go item some case it can improve the fuel ecomeny or increase power but few case it will do both at once ( by altering the fuel curve and timming curve )

For the catyatic converter that useally located before the main muffer useally about a meter ( 3 feet ) behind the engine. most 454 useally use large single catyatic converter but there are few case it may have dual CC's most the 5.7's useally have single CC's you can tell where it was by a short peice of pipe which it was filled in by the pipe clamp or welded marks either way and btw the length useally half meter long ( about 18 inches ) for standard size but for 7.4's it will be 3/4 meter long unless it was plummed for dual exhaust.

There should be one vaccum line that go to the fuel canster which it will be located left front area I think below the head light if my memory serve me right ( My diesel verison do not have the fuel canster at all ) the other one I don't really recall without looking up the service manual book otherwise follow the hood sticker it will show the diagram I know the diagram will show for 7.4 L verison but the 5.7 L verison it should be simauair. so hook it up like that.

I am pretty sure the MAP and O2 sensor is out of wack that why you are using more fuel it should be for your engine.

Check your engine oil and smell for gaz if alot of gaz in there change the engine lube oil ( they can ruin the bearings )

What kind of fuel milage you are getting a rough estame ? I know the 7.4L never get over 10 MPG hiway the 5.7 should hit about 12 to 14 MPG range. but if you are useing " winter " gas the milage will drop some.

You may have to buy a OB scanner to read the computer to see what is going on on tempture and O2 reading and MAP reading and cross refered to the service manual for correct setting for each model ( both 5.7 et 7.4's )

Merci,
Marc
 

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Discussion Starter #20
And when you are buying those replacement sensors, are you telling them it is for a...

1989 Chevy c3500 with a 454?

Or for an [unknown year] caprice with a 350?
I tell them I got an 89 c3500 with a 5.7. I really forget why but I did determine that it is a late 80's model engine. It could be that in 86 or 87 they switched to a serpentine belt instead of using 4 different belts
 
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