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Old 08-06-2009, 10:16 PM   #1
PRUNEDA
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'89 Chevy Trouble Codes 32,34,45

My '89 Chevy truck has a 350TBI. I checked for trouble codes and it gave me 32,34,45. I researched and found the what the codes represent. Which one should I check/replace first? I'm not sure if a bad EGR valvle will trigger a bad MAP Sensor as well. A couple of months ago I installed Edelbrock headers and replaced the O2 sensor while I was at it. Later on I read that it is preferably to install a heated O2 sensor due to the exhaust cooling. Just need suggestions on what/how to check for a faulty sensor. Thanks in advance.

CODE 32-EGR system=
Faulty EGR valve.

Faulty or loose wiring and/or connections at the EGR solenoid.

Faulty, loose and/or leaking vacuum hoses to EGR valve

CODE 34-Manifold Absolute Pressure (MAP) sensor=
Faulty or loose wiring and/or connections at the ECM.

Faulty MAP sensor

CODE 45-Rich Exhaust
Faulty oxygen sensor
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Old 08-07-2009, 08:45 AM   #2
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Re: '89 Chevy Trouble Codes 32,34,45

Code 32 is usually set because the EGR does not work at all. Worry about this last.

The code 34 (MAP code) low voltage that would be caused by high vacuum (that the ECM determined is suspect), which could be a loss of ground issue. A stuck open EGR would cause a low vacuum / high voltage code which is the oposite of what you have.

Anytime this system sets a rich code the first thing you should test is the coolant temperature sensor that the ECM uses because it is one of the criteria used by the ECM to determine how much fuel to inject. It screws into the intake manifold by the Thermostat. If you have an ohm meter I can give you the specs.

This group of codes does not look right to me. I would clear all the codes, drive the truck, and see what codes get set again.

Last edited by ChevyTech; 08-07-2009 at 08:48 AM. Reason: Add more
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Old 08-07-2009, 10:26 PM   #3
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Re: '89 Chevy Trouble Codes 32,34,45

I was hoping you would chime in ChevyTech, I've read some of your replies(in other threads with tons of info) and you're the kind of people that make this site awesome.


Do I clear the codes without replacing any of the parts? I don't have an ohm reader, but I can replace the thermo sensor. I know it's been there for a while, 15+ years. I forgot to mention, the service engine doesn't come on until i'm at 45mph and faster. If I'm around town it doesn't light up. When the truck is at idle, I can feel a slight miss. I'll check out the MAP sensor's negative wire. Thanks
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Old 08-08-2009, 07:31 AM   #4
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Re: '89 Chevy Trouble Codes 32,34,45

ChevyTech is a busy guy, but any time he can give to the problems on this site, he's always appreciated. I appreciate his wisdom. I thank him for sharing it.
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Old 08-08-2009, 07:51 AM   #5
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Re: '89 Chevy Trouble Codes 32,34,45

Quote:
I was hoping you would chime in ChevyTech, I've read some of your replies(in other threads with tons of info) and you're the kind of people that make this site awesome.
Thanks


Quote:
Do I clear the codes without replacing any of the parts?
Yes

Quote:
I don't have an ohm reader, but I can replace the thermo sensor. I know it's been there for a while, 15+ years.
I would not replace any parts yet. This group of codes does not make sense. Wait until we see what else we can figure out.

Quote:
I forgot to mention, the service engine doesn't come on until i'm at 45mph and faster. If I'm around town it doesn't light up.
Clear the codes and then as soon as the light come on, check the codes and see which one gets set first.

Quote:
When the truck is at idle, I can feel a slight miss.
You need to find out why it misfires. This will make the system lose control of the mixture.
These systems work great when every thing is right but they have a big flaw. Once the engine misfires for any reason it throws the system in the wrong direction. This system watches the O2 sensor, but the O2 only will see how much oxygen is in the exhaust stream NOT burnt gas. When every thing is right the O2 knows just how much of the oxygen should have been burned by combustion. Once it misfires, there is way more oxygen in the exhaust, because none got burned in a cylinder. The system thinks it is to lean so it gives the engine a richer mixture. The richer mixture often makes it misfire more (especially if it is cause by weak ignition, bad plugs…) so it dumps in more fuel. Now it is so rich the plugs and O2 sensor get soot on them. It misses more. The system goes richer and richer.

First check for a vacuum leak such as the base gasket under the TBI unit, and the ignition parts would be the next place to look for a problem.

Quote:
I'll check out the MAP sensor's negative wire.
The sensor wires connect to ground at one of the eyelets that are at the front intake bolts or the Thermostat bolts. Make sure they are clean and tight.
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Old 08-08-2009, 08:12 AM   #6
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Re: '89 Chevy Trouble Codes 32,34,45

Quote:
Originally Posted by PRUNEDA View Post
I was hoping you would chime in ChevyTech, I've read some of your replies(in other threads with tons of info) and you're the kind of people that make this site awesome.
Quote:
Originally Posted by ChevLoRay View Post
ChevyTech is a busy guy, but any time he can give to the problems on this site, he's always appreciated. I appreciate his wisdom. I thank him for sharing it.
So many of the people at this are very appreciative of the help they receive it make it a pleasure to help.

It is allergy season for me right now. All my projects get put on hold this time of year, so I have time to sit in the air conditioning away from the pollen and talk with you guys. When the middle of September comes I will be busy catching up and won’t be at the site as much if at all.

Thanks for sharing your appreciation.
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Old 08-08-2009, 12:11 PM   #7
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Re: '89 Chevy Trouble Codes 32,34,45

Allergy season, huh? Fall is my season.....ragweed, kids on the bus, Y3. Right now the humidity and heat are oppressive. Had a big toe nail removed, including the "root", so it's a bit touchy. Add to that a round of stomach "bidness" and it's not all peaches and cream with me. But this site and this forum gives me a chance to visit and socialize with like-minded folks. This is a touch of reality in an insane world that has come to represent my house. Got 5 extra folks living here for up to a year and that includes a pair of 3-year old twins, and I think one is already bipolar. The other has a 4-speed automatic cryer. The 15-year old is typical but makes the twins seem like candidates for child abuse posters (not really). At my age (nearly 62), having the temporary residents makes this forum the santuary for my soul. I appreciate all you guys.
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Old 08-08-2009, 02:10 PM   #8
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Re: '89 Chevy Trouble Codes 32,34,45

Alright ChevyTech, I'll do as you've suggested. I know the plugs should be good installed them when I installed the headers, which was not too long ago. Good luck with your allergies, thanks for your input. I'll keep you posted.
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Old 08-08-2009, 11:53 PM   #9
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Re: '89 Chevy Trouble Codes 32,34,45

I went ahead and cleared the codes. After taking it for a sping the light lite up and rechecked for codes. The only code that came up was 32. I'm going to wait for Monday to purchase the valve from the dealer. I'll keep you posted ChevyTech. Thanks
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Old 08-09-2009, 06:54 AM   #10
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Re: '89 Chevy Trouble Codes 32,34,45

You’re welcome.

Before you buy a new valve do this test:

If you lift the EGR diaphragm with your fingers, with the engine idling, (being careful not to burn yourself or get your fingers caught in the EGR valve) you should hear a definite difference in the way it runs and the engine will most likely stall. If there is no difference you should look for plugged passages.

The passages in the intake manifold can get totally plugged up with carbon.

If you have a hand vacuum pump I can give you more tests to do.

If you find it does need an EGR valve, I would suggest only using a general motors replacement EGR valve.
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Old 08-09-2009, 07:48 AM   #11
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Re: '89 Chevy Trouble Codes 32,34,45

Most definately.
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Old 08-09-2009, 02:20 PM   #12
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Re: '89 Chevy Trouble Codes 32,34,45

Yeah I will only get GM parts. So if I test it as you state above, and there is a difference at idle; does it mean that the valve is good?
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Old 08-09-2009, 02:49 PM   #13
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Re: '89 Chevy Trouble Codes 32,34,45

No; it means the passages are not plugged, so the valve might be bad, but there is also an EGR solenoid that could be bad, or the vacuum hose or vacuum supply.

Make sure vacuum is getting to the EGR solenoid.

Make sure the wiring is still connected to the EGR solenoid.

There are more tests I could give you if you have a hand vacuum pump.
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Old 08-09-2009, 11:03 PM   #14
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Re: '89 Chevy Trouble Codes 32,34,45

Ok I see what you mean. I didn't have time to get to it today, but I will check it out tomorrow evening. I don't have a hand vacum pump, but my friend was telling me that AutoZone rents them. I'll go check the parts store tomorrow.
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Old 08-14-2009, 09:41 PM   #15
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Re: '89 Chevy Trouble Codes 32,34,45

Alright I checked everyting out and the vacum lines were clean. I bought the EGR valve and replaced it. Took it for a spin and the SES light would still light up. My next decision was to replace the EGR solenoid, no luck. The lines are all in decent shape, I don't understand what else to check. I'm still getting code 32.
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Old 08-14-2009, 09:51 PM   #16
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Re: '89 Chevy Trouble Codes 32,34,45

What was the number on the old EGR valve?

Did you buy an OEM EGR valve?
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Old 08-14-2009, 09:55 PM   #17
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Re: '89 Chevy Trouble Codes 32,34,45

Quote:
Originally Posted by PRUNEDA View Post
Yeah I will only get GM parts. So if I test it as you state above, and there is a difference at idle; does it mean that the valve is good?
How big of a difference?

Did the engine die when you opened the EGR valve?
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Old 08-14-2009, 10:32 PM   #18
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Re: '89 Chevy Trouble Codes 32,34,45

The number on the old valve was 17087194. When I lifted the diaphram It was noticable and was close to shutting down. I've been searching and I've found information about a ported vacuum switch. Do you know if these trucks have that switch, I don't remember if I've seen one there.
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Old 08-15-2009, 11:02 AM   #19
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Re: '89 Chevy Trouble Codes 32,34,45

17087194 is a negative backpressure EGR valve.

Port EGR valves use an EVRV (electronic vacuum regulator valve) solenoid.
A ported EGR system is different then a negative backpressure system. Your truck has a negative back pressure system.

Negative backpressure valves should hold vacuum with the engine off. When the engine is started the valve should bleed vacuum. The slightest pulse of pressure in the exhaust system will modulate recirculation (close the valve at least some). A good test for these is to put a hand vacuum pump on the EGR valve and apply vacuum with the engine off and it should hold vacuum. Leaving the vacuum on it, start the engine, and the valve should close.

The negative backpressure EGR has an internal air bleed that is held closed with a small spring when there is no backpressure. When the engine has exhaust backpressure, the small internal air bleed is open and vacuum cannot open the EGR.

Here is a site with a good illustration of a negative backpressure EGR valve.
http://shbox.com/1/EGR_valve.jpg

You should also inspect the vacuum hoses and make sure vacuum is getting to the solenoid that controls the EGR valve.

A comment about your headers:
Exhaust system backpressure can greatly effect the operation of the EGR valves on many vehicles. Modifying the exhaust system can effect how well the EGR works if it changes the pressure in the exhaust system. Exhaust back pressure (from a restricted converter) or no back pressure (from no converter or mufflers) can have an effect on how much the EGR opens.


Another comment I have about your truck:
Any time you install headers a heated O2 sensor should be installed on the vehicle.
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Old 08-28-2009, 05:22 AM   #20
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Re: '89 Chevy Trouble Codes 32,34,45

Havn't had much time to work on the truck lately. I did rechecked the hoses and everything is fine. I remember that the first time the light came on was on the first drive after the headers. I think we're getting somewhere when you mention back pressure. The truck has free flowing catalyic and an unrestricted race muffler. I'm going to install the stock set up and see what happens. I'll start searching for the heated O2. Thanks
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Old 12-03-2009, 12:38 AM   #21
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Re: '89 Chevy Trouble Codes 32,34,45

UPDATE:

After ChevyTech's comment on back pressure, I got to thinking that it had all started after I had installed the headers. As soon as I had a chance I picked up the stock exhaust and reinstalled, and it solved the problem. The truck's SES light did not light up anymore. Awesome, thanks for your help ChevyTech!
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Old 12-03-2009, 01:28 AM   #22
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Re: '89 Chevy Trouble Codes 32,34,45

Headers tend to create more problems than the little gain that you get out of using them. Save the headers for a race car
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Old 12-03-2009, 04:38 AM   #23
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Re: '89 Chevy Trouble Codes 32,34,45

You're welcome Pruneda.

Glad to hear things worked out ok, and thank you for the feedback.

Many people are able to get by running headers on these TBI trucks.

I my opinion if you are going to use headers you should install a heated O2 sensor.

Generally headers improve high RPM performance and the sacrifice of low end power.

I also think headers are a bit of a waste with the heads used on the early (pre vortec) TBI engines.

Last edited by ChevyTech; 12-03-2009 at 04:43 AM. Reason: Add more
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Old 12-06-2009, 12:29 AM   #24
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Re: '89 Chevy Trouble Codes 32,34,45

Thanks
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