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Old 01-11-2019, 05:33 AM   #57
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Originally Posted by sraab928 View Post
I ordered the adaptor. I only had a odb2 reader. I will also have to check the fuel pressure myself as Iím counting on what the shop told me. If you look closely in the video you do see fuel pouring in there though.
Depending on your view, but you might want to eliminate a few potential causes e.g. MAP sensor, IAC valve. Probably cheap fixes and if it doesn't help, you know you have a new unit and a working spare.
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Old 01-11-2019, 05:40 AM   #58
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Quote:
Originally Posted by Boom Sounds View Post
Depending on your view, but you might want to eliminate a few potential causes e.g. MAP sensor, IAC valve. Probably cheap fixes and if it doesn't help, you know you have a new unit and a working spare.
I did replace the MAP sensor - I have a throttle position sensor as well - I did not get an IAC valve but will do that as well.
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Old 01-11-2019, 05:50 AM   #59
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Your video sure sounds like the accelerator pump failing in a
carburator of that era. When the pump didn't work the engine would
stall if you stabbed the gas pedal. But if you accelerated slowly
the engine would run OK.


Since you have a TBI system you probably don't have an accelerator
pump. Is that true? If you accelerate the engine slowly can you
get it to run fast? If so, then your problem must be that you don't
get that extra shot of gas that the engine needs to accelerate.


In a TBI system how does the computer know when to give the
extra shot of gas? Is there a manifold vacuum sensor that

connects to the computer? Is there a temperature sensor that
connects to the computer?
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Old 01-11-2019, 06:05 AM   #60
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Quote:
Originally Posted by sraab928 View Post
I ordered the adaptor. I only had a odb2 reader. I will also have to check the fuel pressure myself as Iím counting on what the shop told me. If you look closely in the video you do see fuel pouring in there though.
I haven't looked at my throttle body while revving the engine but I'm wondering if you're getting to much fuel which is bogging the engine down?

Unfortunately I'm not in a position where I can start my engine to compare.

To my untrained eye that just looked like an excessive amount of fuel coming out of the injectors.
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Old 01-11-2019, 06:10 AM   #61
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Quote:
Originally Posted by bkahler View Post
I haven't looked at my throttle body while revving the engine but I'm wondering if you're getting to much fuel which is bogging the engine down?



Unfortunately I'm not in a position where I can start my engine to compare.



To my untrained eye that just looked like an excessive amount of fuel coming out of the injectors.


I thought the same. My wife asked if maybe itís getting too much fuel pressure. Iím ordering the actron tbi fuel pressure tester this morning. Never gonna hurt to have the proper tools and spare parts on hand.
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Old 01-11-2019, 06:18 AM   #62
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Quote:
Originally Posted by Air345Fly View Post
Your video sure sounds like the accelerator pump failing in a
carburator of that era. When the pump didn't work the engine would
stall if you stabbed the gas pedal. But if you accelerated slowly
the engine would run OK.


Since you have a TBI system you probably don't have an accelerator
pump. Is that true? If you accelerate the engine slowly can you
get it to run fast? If so, then your problem must be that you don't
get that extra shot of gas that the engine needs to accelerate.


In a TBI system how does the computer know when to give the
extra shot of gas? Is there a manifold vacuum sensor that

connects to the computer? Is there a temperature sensor that
connects to the computer?
MAP sensor (manifold air pressure) and TPS (throttle position sensor) along with engine RPM work together to determine how much fuel should be injected.

There is also a temperature sensor that helps the computer to determine the correct mixture.

It will be interesting to see what happens when he slowly pushes on the throttle.

One other possibility I can think of is if work has been done to the injectors at some point, were the correct ones installed? Just a thought.

Brad
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Old 01-11-2019, 07:52 AM   #63
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Old 01-11-2019, 07:56 AM   #64
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My money is still on the throttle body and/or one of the associated sensors.

Is it possible that a partially clogged catalytic converter would also cause those symptoms. Mine has a CC, but not sure whether there were standard outside of California or indeed whether your coach has one.

Quote:
Originally Posted by bkahler View Post
MAP sensor (manifold air pressure) and TPS (throttle position sensor) along with engine RPM work together to determine how much fuel should be injected.

There is also a temperature sensor that helps the computer to determine the correct mixture.

It will be interesting to see what happens when he slowly pushes on the throttle.

One other possibility I can think of is if work has been done to the injectors at some point, were the correct ones installed? Just a thought.

Brad
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Old 01-11-2019, 11:31 AM   #65
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How's this for a long shot: the coach is nearly 30 years old and is reported to have very low mileage. Any chance that it has the original set of spark plugs? Might be worth pulling #8 just to take a look.
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Old 01-11-2019, 12:34 PM   #66
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I will pull a couple plugs to check....

Got it timed today - 4 degrees btdc.

Put in tps -

Results the same .... The IAC is next - napa should have it within the next couple hours - there are two possible choices (12mm or 14mm)- only one avail locally so hoping its the right one - I have mine out to match it up.

I also bought an o2 sensor. Have not installed that yet.

The catalytic converter is also something I have considered - I may disconnect it to see if it has an effect. Its just behind the muffler on this motorhome.

As to slowly increasing rpm - I can get it to a higher rpm that way but it still eventually bogs down (under no load) - In drive (under load) I cant get it much above 2000-2500 rpm

I am learning alot about this motorhome which is good.
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Old 01-11-2019, 01:23 PM   #67
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Quote:
Originally Posted by sraab928 View Post
I will pull a couple plugs to check....

Got it timed today - 4 degrees btdc.

Put in tps -

Results the same .... The IAC is next - napa should have it within the next couple hours - there are two possible choices (12mm or 14mm)- only one avail locally so hoping its the right one - I have mine out to match it up.

I also bought an o2 sensor. Have not installed that yet.

The catalytic converter is also something I have considered - I may disconnect it to see if it has an effect. Its just behind the muffler on this motorhome.

As to slowly increasing rpm - I can get it to a higher rpm that way but it still eventually bogs down (under no load) - In drive (under load) I cant get it much above 2000-2500 rpm

I am learning alot about this motorhome which is good.
Getting the correct parts for the Motorhome chassis is not always as straightforward as one might hope. I spent days (as did Martin and Brad) trying to sort out a fault code on my coach caused by an incorrect knock sensor. One thing I have found useful is the AC Delco parts look up by VIN, which is here:
https://parts-catalog.acdelco.com/ca...log_search.php

I usually cross ref with RockAuto to try and get a clear picture on which is the correct application for my 250.

TBI UNIT MODEL 220 6C1-1 - detailed stuff/parts etc in this section of the Light Truck Unit repair manual, link below

The GM parts wiki goes into even greater detail where you can see blow outs for parts catalogues in different months. A lifetime's work...and worth checking out if you get really stuck for parts
http://www.gmpartswiki.com/query

It works well in concert with the unit repair manual, garage manuals etc

1991_Chevrolet_Light_Truck_Service_Manual
http://www.73-87chevytrucks.com/tech...ice_Manual.pdf

Light_Truck_Unit Repair manual 1991
http://www.73-87chevytrucks.com/tech...air_Manual.pdf

Fuel, Emissions and Driveability 1991
http://www.73-87chevytrucks.com/tech...iveability.pdf

Wiring manual 1991
http://www.73-87chevytrucks.com/tech...ing_Manual.pdf
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Old 01-11-2019, 03:08 PM   #68
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Quote:
Originally Posted by Boom Sounds View Post
Getting the correct parts for the Motorhome chassis is not always as straightforward as one might hope. I spent days (as did Martin and Brad) trying to sort out a fault code on my coach caused by an incorrect knock sensor. One thing I have found useful is the AC Delco parts look up by VIN, which is here:
https://parts-catalog.acdelco.com/ca...log_search.php

I usually cross ref with RockAuto to try and get a clear picture on which is the correct application for my 250.

TBI UNIT MODEL 220 6C1-1 - detailed stuff/parts etc in this section of the Light Truck Unit repair manual, link below

The GM parts wiki goes into even greater detail where you can see blow outs for parts catalogues in different months. A lifetime's work...and worth checking out if you get really stuck for parts
http://www.gmpartswiki.com/query

It works well in concert with the unit repair manual, garage manuals etc

1991_Chevrolet_Light_Truck_Service_Manual
http://www.73-87chevytrucks.com/tech...ice_Manual.pdf

Light_Truck_Unit Repair manual 1991
http://www.73-87chevytrucks.com/tech...air_Manual.pdf

Fuel, Emissions and Driveability 1991
http://www.73-87chevytrucks.com/tech...iveability.pdf

Wiring manual 1991
http://www.73-87chevytrucks.com/tech...ing_Manual.pdf


Thank you for the detailed reply. The part at Napa was not correct. We did use the vin number and rock auto as a reference. Hopefully the correct one will be there in the morning.
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Old 01-11-2019, 04:00 PM   #69
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Thank you for the detailed reply. The part at Napa was not correct. We did use the vin number and rock auto as a reference. Hopefully the correct one will be there in the morning.
What a pain. I put more trust in that AC Delco VIN lookup given that they are the 'official' GM parts supplier, but that isn't fool-proof.

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Old 01-12-2019, 10:22 AM   #70
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Well new iac valve installed and same result. She runs great up until about 2000-2500 rpm. If I push the throttle really slow under no load I can get her to 4000 before she bogs down. My next step is to wait for my obd1 setup to come and use tuner pro rt on the laptop to see whatís going on. I have not looked yet but I assume the connector will be under the dash somewhere?
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