1988 Chevy Suburban

Tiny
FLYINHAWAIIAN6
  • MEMBER
  • 1988 CHEVROLET SUBURBAN
Engine Mechanical problem
1988 Chevy Suburban V8 Four Wheel Drive Automatic

I have a 88 chevy 350 with TBI. It is hard to start and when it starts you have to keep on the gas. If you let off the gas it dies. If you try to put it in gear it dies. I checked the computer and it keeps giving me code 33. I've replaced all the sensors execped the oxygen, and coolant temp sensor. I even temporarily removed the catylitic converter to test if it was a blockage. Tested the fuel pump and filter, nothing wrong there either. Sometimes when I try to start it, it burps a flame out of the throttle boby. I have checked the timing, the heads have been taken off and machined, new gaskets all around, I can't figure out what is wrong with it. Please help.
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Friday, April 3rd, 2009 AT 2:21 PM

12 Replies

Tiny
JDL
  • EXPERT
Hello, maybe you need to clean the throttle-body. With the engine cranking, can you see the injector/s spray pattern, look ok. You can't tell fuel pressure by looking at the spray pattern. What were the fuel pressure specs? I try to check sensor circuits before replacing anything. The code 33 is for the maf sensor. Oops, sorry, map sensor, no maf.
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Friday, April 3rd, 2009 AT 3:00 PM
Tiny
FLYINHAWAIIAN6
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When it started running like crap a friend told me the same thing. I pulled the throttle-body off had it cleaned and new injectors installed. The fuel pump was replaced not to long ago. Maybe 10,000 miles on it. The map sensor is brand new.
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Saturday, April 4th, 2009 AT 3:32 PM
Tiny
JDL
  • EXPERT
Hello, did you get a chance to check fuel pressure, some autostores will loan a fuel pressure gage.

As far as the map sensor, I'd check the circuits, ref voltage--ground-- signal.
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Saturday, April 4th, 2009 AT 3:51 PM
Tiny
FLYINHAWAIIAN6
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I have not yet had a chance to check the pressure. But I will and let you know. As far as map sensor circuits iI ohmed out the wires from the sensor to the ECM they are good. The ref voltage is 4.8
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Saturday, April 4th, 2009 AT 7:23 PM
Tiny
FLYINHAWAIIAN6
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The fuel pressure is 12 psi.
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Sunday, April 5th, 2009 AT 12:22 PM
Tiny
JDL
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Hello, the fuel pressure seems ok. Is there a vacuum source at the map sensor? Anyway you can look at the 02 signal, see if the signal is showing rich or lean?
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Monday, April 6th, 2009 AT 8:33 AM
Tiny
FLYINHAWAIIAN6
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I turned the distributor a little to the left (as you are looking at it under the hood). It now stays idleing by its self, and does not die when you put it in gear. The idle is rough, and I still get a code 33. I'm also getting a code 45. I'm getting 5 in. Of vacuum at the throttle body where the map sensor line plugs in. I pluged the vacuum gage into the intake manifold and the bounces between 6 and 9 in. Of vacuum.
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Friday, April 10th, 2009 AT 4:35 PM
Tiny
JDL
  • EXPERT


http://www.2carpros.com/forum/automotive_pictures/170934_map_sensor_4.jpg



The table above will let you compare the vacuum reading vs signal voltage from the map sensor.

If the vacuum reading you gave, was manifold vacuum at idle, that is too low. Mechanically speaking, the engine should pull better vacuum. Normal is about 17--20. You can check for bad rings, valves, clogged exhaust? Do a compression test on the cylinders.

Code 45 says the system is running rich.
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Saturday, April 11th, 2009 AT 9:27 AM
Tiny
FLYINHAWAIIAN6
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Here is the results of my compression check #1= 150, #3=152, #5= 148, #7= 149, #2=149, #4=149, #6= 151, #8= 128. I took another check 5 min. Later here are those results. #1= 151, #3= 127, #5= 148, #7=126, #2= 124, #4= 126, #6=151, #8= 149.
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Saturday, April 11th, 2009 AT 8:04 PM
Tiny
JDL
  • EXPERT
I don't think your readings look that bad. Generally speaking the reading from the highest to the lowest shouldn't vary more than 20 psi, your close. That is a subjective spec.

With the engine warmed up at idle, What is the voltage signal reading from the map sensor? Is there any vacuum at the map sensor?
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Sunday, April 12th, 2009 AT 10:25 AM
Tiny
FLYINHAWAIIAN6
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The needle on the vacuum gauge bounces between 5 and 8 in. Of vacuum. I will get back to you on the voltage. I'm thinking that I'm geting a map code because there is low vacuum. I'm just learning how this computer crap works so I'm no expert. But my way of thinking is, with the vacuum low, the the sensor is telling the computer that the manifold pressure is screwed up. Like I said I'm no expert so if I'm wrong please correct me. This might be another clue for you. I noticed that with the vacuum gauge hooked to the manifold, my vacuum increased when I gave it gas. To my way of thinking I should have lost vacuum at higher RPM. I got the exacted same result when I hooked the vacuum gauge to the throttle body. At this location that sounds right. Like I said please correct me if I'm wrong.
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Tuesday, April 14th, 2009 AT 10:06 PM
Tiny
JDL
  • EXPERT
A clogged exhaust could cause a low vacuum reading. With a warm engine at idle, if there is no vacuum at the map sensor, it will cause a high voltage signal to the pcm. The pcm may think there is a load on the engine? If the computer does a rationality check between the tps and map sensor, and if voltage signal is high for one sensor and low the other. The pcm will know something is wrong.
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Wednesday, April 15th, 2009 AT 10:34 AM

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