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Old 07-13-2013, 01:17 PM   #1
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1991 25' Airstream 250
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Location of the OBD port

Hi all,

Does anyone know the location of the OBD1 port for my 1991 250 Classic? Also, does anyone know what it looks like?

Many thanks
Nick
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Old 07-15-2013, 04:32 PM   #2
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Hi all - anyone any idea on this one? I think it is meant to be near the steering column

Thanks
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Old 07-15-2013, 05:54 PM   #3
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Originally Posted by Boom Sounds View Post
Hi all,

Does anyone know the location of the OBD1 port for my 1991 250 Classic? Also, does anyone know what it looks like?

Many thanks
Nick
This is what it looks like:
1994 GMC K1500 Truck LS OBD1 on Board Diagnostic Port Connector Chevy 5 7L 4WD | eBay
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Old 08-15-2017, 01:46 PM   #4
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OBD1 location 1991 454 TBI

Nick..wow..your posts pop-up everywhere!
In trying to sort-out my lumpy idle on the 454 TBI, I'm being told that there is, in fact, an OBD1 port connector installed on the 1991n350LE. Trying to find it, I came across your 2015 postings where you asked the same "where is it?" question but could not find a reply?
I'm hearing that if there is a BD1 port then I can use a diagnostic tuning app to tune the ECM but I'm yet to be convinced that there is an ECM 'cause I can't find that either.
Any thought or comments but I need to get the engine to idle and run much smoother. Thanks, Chris
https://youtu.be/eqNeZvZqfCw
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Old 08-15-2017, 03:40 PM   #5
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Chris, you do have a TBI system. I can see the MAP sensor located to the right of the air filter housing sitting just above right valve cover.

I don't know where your OBD1 port is but if you do find it you can buy a cord ($85) and download one of several apps on your phone. That will allow you to monitor all of the system parameters and to create log files that you can then open in excel.

I listened to the video with your idle and I don't know that the lumpiness is coming from the cam. I'm planning on listing to it again this evening when I can turn the audio up louder.

Brad
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Old 08-16-2017, 08:28 AM   #6
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OBD1 location

Brad...I've replaced the MAP sensor you noted but my quest is to locate (if it exists!) the OBD1 data link connector...if available, yes I would love to dongle it and read and save parameters.
Your comment re cam is interesting as this indeed is my first thought for the lumpy idle. Trying to find out from Crane if this could be too aggressive on idle but so far indications are "no"....maybe fitting the revised cam into the original engine ECM/sensor set-up could be the cause?
Hope your listening can throw further light on this...many thanks
chris
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Old 08-16-2017, 09:01 AM   #7
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Brad...I've replaced the MAP sensor you noted but my quest is to locate (if it exists!) the OBD1 data link connector...if available, yes I would love to dongle it and read and save parameters.
Your comment re cam is interesting as this indeed is my first thought for the lumpy idle. Trying to find out from Crane if this could be too aggressive on idle but so far indications are "no"....maybe fitting the revised cam into the original engine ECM/sensor set-up could be the cause?
Hope your listening can throw further light on this...many thanks
chris
Chris, my comment about the MAP sensor was in response to your statement "but I'm yet to be convinced that there is an ECM ". If you have a MAP sensor then you have an ECM somewhere!

The ECM will most likely be inside the cab somewhere as would be the ALDL port. None of the earlier ECMs were mounted in the engine compartment that I know of.

Reading through your previous posts it didn't dawn on me until just now that you installed a different profile cam compared to the stock cam. I believe that can definitely affect your idle AND driving performance. The ECM is programmed to handle certain air/fuel ratios at various RPMs based on throttle position, MAP sensor reading, coolant temperature, etc.

Changing the cam will change the amount of air or fuel required at any given point. The only way to change that is to have a "tuner" collect operating data and then adjusting the various tables in the ECM to account for the change in the cam.

This is the process I've been going through with my new engine build. The odds are your system is close but for optimum performance you may want to contact a good TBI tuner and have him adjust the various tables for you.

This is a task Peter has been performing on his 310 only he's been doing the adjustments himself. If you would like I can provide you with the contact info for the guy doing my tuning.

Brad
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Old 08-16-2017, 01:15 PM   #8
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OBD1 found!

Found the OBD! socket hiding and tucked-up under the dash. It's a 12 pin so I am getting a 12 to 16 pin dongle so as to connect to my reader.
for future forum reference, the connector socket was located up under the dash molding close to the right-hand side of the steering column.
Here are the codes
https://repairpal.com/gm-obd-I-code-chart
Pictures of sockets and converter dongle
Attached Images
  
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Old 08-16-2017, 01:34 PM   #9
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The OBD port on my 1991 350LE is on the right side of the column, tucked up behind the dash. It was hard to find.


Regards,

JD
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Old 08-16-2017, 04:12 PM   #10
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Eureka!

Brad...yes, I agree that the new Crane cam probably needs to re-program the ECM. Now that I've found the port, this is the next job. Re-programming the ECM chip does not seem trivial and may be way beyond somehting I want to tackle. I guess the first step will be to read the OPBD1 codes and go from there.
I've been chatting with Peter but would like to know how to contact your TBI tuner as I think we will need to get his expertise.Thanks
chris
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Old 08-16-2017, 04:45 PM   #11
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Originally Posted by chriscraw View Post
Brad...yes, I agree that the new Crane cam probably needs to re-program the ECM. Now that I've found the port, this is the next job. Re-programming the ECM chip does not seem trivial and may be way beyond somehting I want to tackle. I guess the first step will be to read the OPBD1 codes and go from there.
Let's put it this way, I'm an Automation engineer by trade which means I write programs for a living. There's enough involved in reprogramming an ECM that I have no desire to learn what it takes to tweak the tables to get things to run right! That's why I hired someone that knows what he's doing

Quote:
I've been chatting with Peter but would like to know how to contact your TBI tuner as I think we will need to get his expertise.Thanks
chris
PM me your address and I'll send an email to my Tuner introducing you to him. You can take it from there.

Brad
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Old 08-17-2017, 11:35 AM   #12
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Hi guys

Still in a very hot and sunny Perigord (Southern France). The OBD1 port is just below the steering column. Look down by left hand side and you will see it. You can short out pins to read codes, but to achieve anything on the tuning front, I think you need to be able to read the diagnostics. I recently bought a unit from Ebay. Brad has been trying it out with a bluetooth OBD1 diagnostics sender to an Android device. According to Brad, it seems to work.
However, I'm with Brad that any re-programming of the OBD1 chip is a specialist job.
I'm in no rush for the bluetooth device, so if you want to try it out, I'm happy for Brad to ship it to you and you can send it on to me later (I'll pay the shipping).

Au revoir!

Nick and family xx
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Old 08-17-2017, 11:50 AM   #13
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Sorry, I've just ready the replies and realise you are further down the line. A few comments:

I am not sure the 16 pin to 12pin converter will work, unless you are sure your reading device supports OBD1. I tried the 16:12 with a reader I had and it didn't work. Even if it does work, my old code reader was very limited in function. I think the new bluetooth device linked to ALDL Scan, ALDLDroid, TTS Datamaster or TunerPro RT is far more powerful.

GM did produce a specific OBD1 code reader for their garages. I have seen one in the UK, but cannot confirm its functionality.

This was the fella I ordered from ebay. It blew a fuse at first, but the response and comms from the seller was good. He shipped replacements immediately and I think after that, no probs.

https://www.ebay.co.uk/sch/1320elect...1&_ipg=&_from=

I would have thought it possible to run the readings and then send the code and then either get a new PROM or send your PROM for re-programming. I would have though the former preferable. The PROM chip itself is in the grey box mounted below the OBD1 port. You can open it up and get the PROM code off the top of it. It's a small blue chip within the grey box.

Box looks like this:
http://www.ebay.com/itm/S10-BLAZER-J...-/311932178448

PROM chip looks something like this:
http://images.wrenchead.com/Smartpag...47_PRIMARY.jpg
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Old 08-17-2017, 12:21 PM   #14
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When you get a light on the dash, you can read the codes via the 'paper clip' method. This will the allow you to cross reference against your code table.

The bluetooth device will give you diagnostic readings to show where you are within the parameters for each code, so far greater granularity with real timing readings against various criteria. I don't have access to an example at the moment, but I think Brad might have one.

Out of interest, have you checked your timing? I think base timing is 4 degrees before top dead centre. There's a tan and black wire which you have to disconnect first, then you can crawl under the vehicle and you'll see a timing mark which you can use with a timing light. Guidance in the chassis manual, I think.

As you know, I had lumpy running with occasional loss of power on the 250 last year. I replaced many of the potential culprits e.g. MAP sensor, new leads, distributor cap, rotor, coil, ignition control module, pickup, fuel filter, oxygen sensor, EGR valve, that tube thing we discussed previously, MAP sensor, Positive Crank Ventilation (PCV) Valve.

I also rebuilt the TBI. I am happy I replaced all those small items, relatively low cost and peace of mind on the road that I have eliminated some potential issues. However, I am pretty sure my issues where caused by the TBI. I reckon the TBI rebuild solved my problems. If anyone ever attempts this (It's pretty straightforward), you need to be really specific about the TBI unit and get the casting number off the existing unit. I found a reliable seller on ebay who sold a rebuild kit. Fingers crossed, we are now a few thousand miles down the road and no loss of power. I don't think this would cause the issues you describe.

all the best
Nick
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