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#1 |
Registered User
Join Date: Sep 2014
Location: Texas
Posts: 215
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Re: 86 GMC Sierra Classic 2500 questions
After looking at my '85 I see that you are plugged into the correct port and your adapter has no port.
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#2 |
Registered User
Join Date: Feb 2012
Location: Morgantown, Wv
Posts: 294
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Re: 86 GMC Sierra Classic 2500 questions
Either way this port needs to be capped, Or used.
__________________
87 V20, Vortec 350, Sm465, Np205, Dana 44, 14bff 4.10's |
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#3 |
Registered User
Join Date: Aug 2012
Location: San Jose, California
Posts: 96
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Re: 86 GMC Sierra Classic 2500 questions
Thanks for the advice. There was never anything over that port since I've had the truck.
I'm also curious if someone can tell me what this black Casco box is. I cannot find any information on this thing online. |
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#4 |
Registered User
Join Date: Sep 2014
Location: Texas
Posts: 215
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Re: 86 GMC Sierra Classic 2500 questions
Google search says its an "AIR injection valve control module". For '86 C/K 20,30 350M. Can't help you beyond that. Not something I remember dealing with.
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#5 |
Registered User
Join Date: Aug 2012
Location: San Jose, California
Posts: 96
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Re: 86 GMC Sierra Classic 2500 questions
So on top of my other problems I still have leaky intake bolts. The other day I used Permatex High Heat Threadlocker per the advise of the guy at Advance Auto Parts, waited 24 hours as recommended. I took it for a drive and oil still pools up! Also noticed the dipstick came loose. The pressure gauge reads between 40 and 50 usually and I thought that was normal. Is this too high?
Any recommendations for the oil leaking through the bolts? Permatex High Heat didn't seem to work and I thought I used enough. |
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#6 |
Registered User
Join Date: Sep 2014
Location: Texas
Posts: 215
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Re: 86 GMC Sierra Classic 2500 questions
Check your valve cover bolts and gaskets.
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#7 |
Registered User
Join Date: Aug 2012
Location: San Jose, California
Posts: 96
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Re: 86 GMC Sierra Classic 2500 questions
Thanks jetmech. I guess I just assumed oil was leaking through the intake manifold bolts.
Thanks to this site I have solved many of my problems. Finally got my instrument cluster lights to work along with the exterior lights except the tail lights will not come on when I turn on the headlights. All other lights are doing their job. All fuses have been replaced and wires checked. I'm thinking the switch might need to be replaced. Anything I else I should check before replacing the switch? Also on my fuse box I have a port for ECMB and ECMI but no connections for a fuse to stick in there. Is this a problem? All of the fuses in the pic have been replaced and put in properly. I don't know why some were upside down and the improper fuse was in the radio port. |
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#8 |
Registered User
Join Date: May 2007
Location: New Hampshire
Posts: 349
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Re: 86 GMC Sierra Classic 2500 questions
On your truck the black box with the Casco on it was what passed for the "ECU/ECM" (computer). It had only one function. As jetmech85 suggests, it controlled the A.I.R. system diverter valves under certain conditions. It had two inputs;
1. Engine speed - it used the white wire that is lead out of the distributor cap (the same wire is used to drive a tachometer) 2. Incoming combustion air temperature - measured by a sensor that mounted through the side of the air cleaner. Since your A.I.R system as been stripped, it can be removed. On your tail light issue - just be sure that the correct bulbs are installed. You'd be surprised how often a single filament bulb gets jammed in to that dual filament socket. Are your license plate lamps and rear markers working? If they are, that would indicate that power is available in the rear lighting wire harness on the brown wire (feeds the plate, rear markers & rear parking) and the problem is within the dual filament socket/bulbs. |
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#9 |
Registered User
Join Date: Sep 2014
Location: Texas
Posts: 215
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Re: 86 GMC Sierra Classic 2500 questions
Put the proper amp fuse in the radio slot. Being upside down makes no difference. I have some empty slots on my Suburban also since there is no computer. You have most lights working so probably not the switch. Follow chengny's suggestions and also you may want to buy a test light.
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#10 |
Registered User
Join Date: Aug 2012
Location: San Jose, California
Posts: 96
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Re: 86 GMC Sierra Classic 2500 questions
That picture of the fuse box was old, all of the fuses have been replaced with the proper ones. All of the rear bulbs have been replaced with the proper bulbs. The only ones that have not been replaced are the license plate bulbs. I also found a bulb up under the rear bumper which I have no idea what it is for. It is not connected to anything. In the picture you will see the rear wiring. Under the electrical tape there is a brown wire that is connected to the two license plate bulbs. The license plate bulbs and the taillights still do not work, however brakes turn signals and everything else work properly.
I am also working on brakes. As I was bleeding the right rear, one of the rear brake lines was badly rusted and leaked. I took it out and brought it to the local auto parts store. They gave me a new piece of brake line and a tube bender. But I didn't realize that the fittings were different sizes at each end, of course. I think one of these pictures is what you call a junction box? This junction box is the one with the larger fitting. Do you think the auto parts store will have brake line with two different size fittings at each end? Or does anybody have a suggestion on how to reuse the original fitting? |
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#11 |
Registered User
Join Date: Aug 2012
Location: San Jose, California
Posts: 96
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Re: 86 GMC Sierra Classic 2500 questions
My phone would not let me upload more than one picture at a time for some reason so here are the brake pictures. The line fitting from the auto parts store fits this end.
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#12 |
Registered User
Join Date: Aug 2012
Location: San Jose, California
Posts: 96
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Re: 86 GMC Sierra Classic 2500 questions
The fitting at this junction is much larger.
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#13 |
Registered User
Join Date: Jul 2011
Location: back 40, bc
Posts: 3,817
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Re: 86 GMC Sierra Classic 2500 questions
that is a rudimentary ABS system. designed to prevent wheel lock-up with a empty or lite load. just by pass it so you only have one size fitting. there notorious for jamming, hanging up, etc. i got rid of mine & the brakes feel a lot better.
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#14 | |
Registered User
Join Date: Jun 2014
Location: Orlando Florida
Posts: 1,598
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Re: 86 GMC Sierra Classic 2500 questions
Get an adapter or you can use that piece if you cut then reflare the line.
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Quote:
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#15 |
Registered User
Join Date: May 2007
Location: New Hampshire
Posts: 349
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Re: 86 GMC Sierra Classic 2500 questions
![]() This is called a "height sensing valve" and is part of the load compensating system. It works together with the proprtioning/compensating valve as follows: These vehicles use either a two function or three function combination valve. Some vehicles use a height sensitive proportioning valve in addition to the combination valve. The two function combination valve consists of a metering valve and a brake failure warning switch. The hydraulic brake lines are routed through this valve to the wheel cylinders or calipers. The metering portion of this valve assists in providing balanced front to rear braking by delaying full hydraulic fluid pressure to the front disc brakes until the rear drum brakes overcome return spring tension and the linings contact the drums. The brake failure warning switch portion of the valve activates the brake warning lamp when there is a loss of pressure in either the front or the rear braking system. The three function combination valve consists of a metering valve, a brake failure warning switch, and a proportioning valve. The metering valve and brake failure warning switch operate the same as those in the two function combination valve previously described. The proportioning section of the valve proportions outlet pressure to the rear brakes after a certain rear input pressure has been reached, preventing rear wheel lock-up. The height sensitive proportioning valve provides ideal brake balance according to weight at rear axle. This valve is mounted on the frame and responds to changes in vehicle trim height in relation to rear axle load. Mechanical linkage connects the valve to a bracket attached to the rear axle. It was a bad idea. GM gave up on it within a couple of years. This TSB was issued in 1988: Brakes - Rear Brake Sensitivity GMC NUMBER: 88-T-151 GROUP: 5 - Brakes DATE: August, 1988 CORPORATENUMBER: 865010R SUBJECT: REAR BRAKE SENSITIVITY - HEIGHT SENSING VALVE REMOVAL MODELS: 1984-86 C/K 3500 AND 1987-88 R/V 3500 THIS BULLETIN IS A REVISION OF TRUCK SERVICE BULLETIN 85-B-79, DATED MAY, 1985, UPDATING FOR MODEL YEARS 1984-1988. 1984-1986 C/K 3500 and 1987-1988 R/V 3500 series trucks are equipped with a rear suspension height sensing device that optimizes the brake proportioning valve setting for the load the vehicle is carrying. The height sensing system adjusts the brake balance in vehicles subjected to a range of loading conditions. Occasionally, vehicle modifications by body builders or owners influence the height sensing device. If a vehicle has had rear suspension modifications that affect its trim height or the spring rate, and the driver comments about the brake modulation characteristics of the vehicle, it is recommended that the height sensing system be removed and the brake system be revised as described below: |
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#16 |
Registered User
Join Date: May 2007
Location: New Hampshire
Posts: 349
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Re: 86 GMC Sierra Classic 2500 questions
On your parking/marker/plate lighting issue. Here is a good way to start the diagnostic;
All of these lamps are supplied with power on the brown lead which is one of four circuits that make up the rear lighting harness. The other three are: Back up lights - light green Left Directional/brake - yellow Right directional/brake - dark green Schematically, the rear lighting harness looks like this (diagram compliments of chuckschevytruckpages): ![]() Here is what the actual harness looks like when layed out on the floor; ![]() Climb under the rear end and locate the weather-tite style connector as shown below: ![]() Separate the connector and - with the headlight switch in the parking light position - check for voltage on the brown lead at the cab side of the connector. If you get power at the brown lead (on the cab side of the connector) - the problem is in the rear lighting harness. If not, the problem is in the forward side. Do your courtesy (underdash) lights work when you open the door? How about your dome light? These lights are on the same circuit, so if they work, the problem is in the H/L switch or the wiring between the H/L switch and the weather-tite plug at the rear harness connection. |
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#17 |
Registered User
Join Date: Aug 2012
Location: San Jose, California
Posts: 96
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Re: 86 GMC Sierra Classic 2500 questions
Thank you chengny. I will thoroughly inspect the rear wiring later today. I don't know if mine is different thatn the pictures you posted but when I was under there before I did not see the connector you are talking about.
In the picture where the red circle is there is a brown wire that had been soldered to only the license plate bulbs (under the electric tape). One black wire to each bulb soldered to the brown wire. The yellow circle is a loose connector that runs to a bulb that is under the bumper. What is this bulb and does it matter that it is not connected to anything? I don't have a picture of that right now. When I was under there I did not see the "weather-tite style connector" that you are talking about but I will take a closer look. Thanks for all of your valuable information. The dome light and courtesy lights work. However the instrument cluster lights work intermittently, Sometimes if I jiggle the switch just right the cluster lights will stay on.... I know, ![]() One other thing I wanted to ask about the odometer. Mine is at 45,000 miles... Obviously it reached it's limit and started from zero again. It's probably more likely to be at 345,000 or more miles. How high do the odometers go on these trucks before rolling over to zero again? |
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#18 |
78K & 79C Jimmys
Join Date: Nov 2009
Location: Ottawa Ont CANADA
Posts: 7,901
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Re: 86 GMC Sierra Classic 2500 questions
do yourself a favour and get rid of those blue connecters
they cause lots of probs, basicly cutting wires,allows moisture/salt in they prob used it to connect a trailer harness. may have removed the plugs too. the cluster dimmer is controlled by a coil of wire that can burn out in spots, a rheostat,if the switch is out (of dash)you can usally see it,might see the burn marks too thats why it can work off and on when twisting the nob the od goes to 99,999 then 0,later years have another digit
__________________
John 1978 GMCJimmy4X4-350/203 1979 GMCJimmy4X2-305/350 |
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#19 | |
Registered User
Join Date: Aug 2012
Location: San Jose, California
Posts: 96
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Re: 86 GMC Sierra Classic 2500 questions
Quote:
I want to apologize for not taking your advise when you said to get rid of the blue connectors. It turns out the connection for the tail lights, side markers and license plate lamps was bad.... I wish I had listened. I finally did what you said and now all of the lights work. I promise I will listen this time. So I replaced the coolant temperature sensor along with the thermostat after finding out that it was stuck open. Now after about five minutes the gauge approaches 260°. I'm not feeling a whole lot of pressure in the upper radiator hose and I'm getting a squealing noise on occasion. I'm thinking this might be the water pump. Is there something else I should look at first? I don't know if it matters but I replaced the thermostat with one of those failsafe ones. After-the-fact I realized that might have been a bad idea. The one that was in there was a Robertshaw 330-180. I'm thinking I probably should have replaced it with that same one. Everything seemed fine when the thermostat was stuck open and it was running cold. Now my question is does it sound like the water pump needs to be replaced or something else? Any advice on this issue? |
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#20 | |
Registered User
Join Date: May 2009
Location: Motor City
Posts: 9,194
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Re: 86 GMC Sierra Classic 2500 questions
Quote:
k
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Chevrolet Flint Assembly 1979-1986 GM Full Size Truck Engineering 1986 - 2019 Intro from an Old Assembly Guy: http://67-72chevytrucks.com/vboard/s...d.php?t=342926 My Pontiac story: http://forums.maxperformanceinc.com/...d.php?t=560524 Chevelle intro: http://www.superchevy.com/features/s...hevy-chevelle/ |
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#21 |
Registered User
Join Date: Aug 2012
Location: San Jose, California
Posts: 96
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Re: 86 GMC Sierra Classic 2500 questions
I always realize how dumb some of my questions are after it's too late. It should have been obvious how high the odometer went since there are only 5 digits + the 1/10.
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#22 |
Registered User
Join Date: Feb 2012
Location: Morgantown, Wv
Posts: 294
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Re: 86 GMC Sierra Classic 2500 questions
99999.9
__________________
87 V20, Vortec 350, Sm465, Np205, Dana 44, 14bff 4.10's |
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#23 |
Registered User
Join Date: Aug 2012
Location: San Jose, California
Posts: 96
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Re: 86 GMC Sierra Classic 2500 questions
I bet this one rolled past 99,999.9 about 5 or 6 times by now.
![]() When I was messing with the headlight switch under the dash I did actually notice a little melted plastic on the switch. |
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#24 |
Registered User
Join Date: Aug 2012
Location: San Jose, California
Posts: 96
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Re: 86 GMC Sierra Classic 2500 questions
I have searched all over this site an have not found a solid answer to this issue. So there is some kind of vacuum valve right above the brake pedal and when I press the brakes it makes the hissing noise. I have read a lot about bad boosters, etc but the brakes seem to be working great and I really do not think it is a bad booster. I saw one post where a guy said, "it was a vacuum plunger like switch that was connected to the brake pedal. I guess it was used to kill the cruise when the brakes we engaged."
Apparently he just disconnected the vacuum line that led to just above the brake pedal and it solved the hissing problem. On my truck "electronic speed control" was one of the options. I assume that is the same as cruise control... Was he correct? Was this just something to disengage the cruise control? |
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#25 |
78K & 79C Jimmys
Join Date: Nov 2009
Location: Ottawa Ont CANADA
Posts: 7,901
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Re: 86 GMC Sierra Classic 2500 questions
yes follow it and it will end at the CC under the hood(my 88)
not using it?be sure the other lines are sealed off too
__________________
John 1978 GMCJimmy4X4-350/203 1979 GMCJimmy4X2-305/350 |
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Tags |
1986, 2500, brakes, gmc, sierra classic |
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