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Old 05-13-2007, 07:20 PM   #1
bmwpower
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Default Chevy guys: troubleshooting 350 engine...FIXED!!!

My Dad's Suburban (1990) is acting up. It won't stay running and/or start up. If you let it sit for a while it starts up, but runs rough - seems like it's running rich. Today I had it running, but it eventually died and we couldn't start it up again. Check engine light is on.

Any idea where I should start looking? All the vacuum lines look good. Not sure how to pull codes on this truck.

Any help is greatly appreciated!
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Old 05-13-2007, 07:38 PM   #2
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Default Re: Chevy guys: troubleshooting 350 engine

I had a Suburban the same year. With the same type of situation. Mine turned out to be the fuel pump. However, most all of the fuel pumps for that year were electric. Usually when they go out, they just die. I would check the following:

Does it have fuel? Is it fresh with no moisture in tank.
Clogged fuel filter
Fuel pump
Electronic fuel injection or carburator needs cleaned and overhauled.
Check you distributor, cap and coil, plugs & wires.

Check the basics first.
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Old 05-13-2007, 07:54 PM   #3
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Default Re: Chevy guys: troubleshooting 350 engine

Quote:
Originally Posted by Poltax View Post
I had a Suburban the same year. With the same type of situation. Mine turned out to be the fuel pump. However, most all of the fuel pumps for that year were electric. Usually when they go out, they just die. I would check the following:

Does it have fuel? Is it fresh with no moisture in tank.
Clogged fuel filter
Fuel pump
Electronic fuel injection or carburator needs cleaned and overhauled.
Check you distributor, cap and coil, plugs & wires.

Check the basics first.
Tune up was done by Chevy dealer <<5K miles ago - plugs, wires, cap, rotor, etc. I'll have to check, but I guess the fuel filter was done at the same time. Fuel should be good

When I pulled the air cleaner cover and looked down into the carb, I could see fuel getting sprayed into the carb, so I would think fuel supply should not be a problem. It's definitely running rich (when it runs) because I can smell fuel out the exhaust pipe.
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Last edited by bmwpower; 05-13-2007 at 07:59 PM.
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Old 05-13-2007, 08:22 PM   #4
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Default Re: Chevy guys: troubleshooting 350 engine

You didn't tell the mileage, so that leaves it difficult to totally diagnosis. If I have to guess, I am going to lean toward a bad ignition module. Once it gets hot, the wires in the coil short out. When it cools, the wires in the coil separate enough to give a spark. The spark is weak so it will run crappy. I am a mechanic from the old days, prior to all this emission and pointless ignition stuff, so I have limited experience with all this new crap, but that is where I would start based on my limited experience.
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Old 05-13-2007, 08:59 PM   #5
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Default Re: Chevy guys: troubleshooting 350 engine

Back when I was in the USMC one of my buddies took his car into the place on base to have it tuned up. Ran fine for a couple days then progressively ran worse & worse until it wouldn't start at all. Come to find out they never tightened the distributor hold down bolt down which left the distributor loose to rotate at will. Another time I decided to take the scenic route one day coming back on base & had the ignition module go out on my camaro, one minute it ran great then just died. It would crank but wouldn't start no matter what until we figured out what it was & replaced the module in the distributor then it fired right up & ran like a top again. I had probably around 40,000 mi on the camaro when this happened. Did it suddenly get like this or did it start running poorly over time?
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Old 05-13-2007, 09:14 PM   #6
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Default Re: Chevy guys: troubleshooting 350 engine

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Originally Posted by SteveU View Post
Back when I was in the USMC one of my buddies took his car into the place on base to have it tuned up. Ran fine for a couple days then progressively ran worse & worse until it wouldn't start at all. Come to find out they never tightened the distributor hold down bolt down which left the distributor loose to rotate at will. Another time I decided to take the scenic route one day coming back on base & had the ignition module go out on my camaro, one minute it ran great then just died. It would crank but wouldn't start no matter what until we figured out what it was & replaced the module in the distributor then it fired right up & ran like a top again. I had probably around 40,000 mi on the camaro when this happened. Did it suddenly get like this or did it start running poorly over time?
The truck has a little over 100K on it. It used to run like a brand new truck until just recently. Now it idles high when it is running and just won't start most of the time.

You think it's one of these ignition modules? Or something to do with the distributor?

When I had it running tonight (sat for like ~2 weeks before I think) it ran for 5-10 minutes and then just quit. Sounds like something that could be attributed to heating/cooling of a component.
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Old 05-14-2007, 08:20 AM   #7
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Default Re: Chevy guys: troubleshooting 350 engine

Timing chain is a good possibility with that mileage.

Scott
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Old 05-14-2007, 08:35 AM   #8
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Default Re: Chevy guys: troubleshooting 350 engine

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Timing chain is a good possibility with that mileage.

Scott
Timing chains go in 100K??
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Old 05-14-2007, 09:36 AM   #9
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Default Re: Chevy guys: troubleshooting 350 engine

Here is some info I found on how to pull the check engine codes:

Under the radio by the driver's right knee you'll see a connector with two rows of pins. That is the ALDL (Assembly Line Diagnostic Link) connector.Pin A is in the upper right-hand corner (as you're looking at it), PinB is right beside it.
Bend a paper clip or small piece of wire into a U shape and insert it into both pins A and B so that they are connected together.
Turn the ignition switch to the ON position, but don't start the car.
You'll see the "Check Engine" (or "Service Engine Soon" on some models) light flash some codes.
Error codes are two digits, and the light flashes out the first digit, pauses, and then the second digit. It will repeat each code two more times (total of three) before displaying the next one. The first and last code will always be a code 12 (flash, pause, flash, flash, long pause, repeat). This code is normal and means that no tach signals are making it to the computer (because the engine isn't started). If you don't get a code 12, something is wrong with your jumper or your computer.
Make a note of any codes that come up and look them up on the chart. Here is a chart listing the computer error codes. It is in Microsoft Word 6.0/95format. I recommend printing out this chart and keeping it in your glove box along with an official GM diagnostic paper clip. Shrink it to 1/4 pagesize and then laminate or coat with clear tape and it'll last a while. The chart says what each code is and some common causes. From there it's your call whether the problem is serious enough to keep driving the car or not, and how urgently service is required. Troubleshooting each code is beyond the scope of this web site and if you need to do so you should either get a manual (Factory, Haynes or Chilton's) or take it to a mechanic who can do further diagnostics on a diagnostic scope.
Remember to remove the jumper before running the car.
If you think you've fixed a problem and need to clear the existing computer error codes, just disconnect the battery (for a few seconds is plenty) and reconnect it.


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Old 05-14-2007, 09:37 AM   #10
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Default Re: Chevy guys: troubleshooting 350 engine

it's a gm...

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Old 05-14-2007, 10:19 AM   #11
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Default Re: Chevy guys: troubleshooting 350 engine

Quote:
Originally Posted by bmwpower View Post
Timing chains go in 100K??
Most chevy or BOP v-8 engines I have had (which catches most everything I have ever had) generally shuck the timing chain somewhere in the 100K mile neighborhood.

I think I would want to check the timing first. That would be a good jumping off place.

I do not think it would be an ignition control module simply because with those that i have worked with, the icm either works, or it does not. As indicated in a prior post, usually when they go out, it acts just like turning the switch off, except once it goes, there is no restarting it till you replace the icm. Fords, or at least the one i owned went out gradually, and over a several weeks period. You could wait till it cooled off, then restart it till it finally got bad enough it just died.

If the timing is fine, I would also look at the computer.

You should be able to pull codes on that truck if you check into it. That would likely be the best thing to do early on after checking timing.

Good luck, and I will post more if something comes to mind!
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Old 05-14-2007, 10:28 AM   #12
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Default Re: Chevy guys: troubleshooting 350 engine

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it's a gm...

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Old 05-14-2007, 12:01 PM   #13
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Default Re: Chevy guys: troubleshooting 350 engine

totally dead on with checking the trouble codes from the ECM.
It's a GM tbi unit on that year truck, so there's precious little that can go wrong with it. As stated before, it's more likely than not a problem with an electronic widget, like the ignition module, which is under the distributor cap, an O2 sensor on the exhaust manifild, or the throttle position sensor on the throttle body. these are all known 'hot spots' on GM TBI. but before you do ANYTHING or buy any parts, I would thoroughly check the vacuum lines and hoses. GM systems of that vintage run off a map sensor (the five -sided widget on the firewall) and thus they are EXTREMELY sensitive to vacuum leaks. check the line to the MAP Sensor, and check the breather line from the valve cover and the EGR to the air cleaner housing.

if all that fails, check the EGR with a mity-vac to make sure it operates smoothly.
that's all I got!
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Old 05-14-2007, 12:35 PM   #14
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Default Re: Chevy guys: troubleshooting 350 engine

I think that a vacuum leak could be quite likely, additionally I think the tps could also be highly suspect. Indeed, both are logical suspects.
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Old 05-14-2007, 05:37 PM   #15
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Default Re: Chevy guys: troubleshooting 350 engine

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Originally Posted by bmwpower View Post
Timing chains go in 100K??

Pontiac's go in 60K......... Chevy's take a little longer....
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Old 05-14-2007, 06:21 PM   #16
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Default Re: Chevy guys: troubleshooting 350 engine

The idle air control module (IAC) on the TBI is a likely suspect as well.
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Old 05-14-2007, 07:30 PM   #17
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Default Re: Chevy guys: troubleshooting 350 engine

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Them thar are fightin words for bowtie boys!

Im aloud to say that, I own 2 GMs lol.

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Old 05-14-2007, 07:52 PM   #18
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Default Re: Chevy guys: troubleshooting 350 engine

Disconnect the battery for a few minutes to see if erasing the computer memory helps. There should be a way to check the resistance of the coil. I have seen more bad coils in HEI then modules.
I have had the same experience with modules, they are either alive or dead. If you touch them, they die.
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Old 05-14-2007, 08:42 PM   #19
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Default Re: Chevy guys: troubleshooting 350 engine

OK....

I stopped over again to take a look at the truck. It did the same thing tonight:

1. Start the truck. It starts up but run rough.
2. Shut it down and try to restart the truck. It won't start.

I took off the gas cap after trying to start the truck and a lot of pressure escaped. Not sure if this is normal as we don't pump our own gas in NJ, but I thought I'd mention it.

The fuel filter appears to have been replaced at the time of last tune up (<5k miles).

Fuel is still flowing as seen when looking into TB with the air cleaner off.

I pulled the check engine codes (thanks 74NovaSS) and it's failing for "Cooland sensor/low temp" (code 15). After I told my Dad this, he remarked that the temp gauge was acting up and would swing back and forth all the time. I pulled the harness and tried to start it up, but no go. I replaced the temp sensor with a new one and let it hang in the air, still no go. I didn't see how the temp sensor would affect startup anyway.

I disconnected the battery, reconnected and then tried to start the truck up again....no go.

I checked all the hoses again for vacuum leaks and couldn't find anything.

I checked the EGR by pushing the diaphram with my fingers. It moved in and out, so I guess it's okay.

I'm not sure what the MAP sensor is or where it's located.

I bought a Haynes manual so I'm going to try and test some of these modules tomorrow....we'll see....
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Old 05-14-2007, 09:02 PM   #20
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Default Re: Chevy guys: troubleshooting 350 engine

buy an ignition coil and replace it. At 100K it is about time for a replacement. They are like spark plugs.... they do wear out.
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