After a few local trips, it was time to break the Suburban in for real. A 900 mile trip to Florida from Pennsylvania. What could possibly go wrong? Fairly quickly we found out a previous owner had spliced together the high and low beams at the headlights, which resulted in the wiring overheating and constantly triggering the breaker in the light switch. Since half the drive was at night, it was a pain and we finally gave up and waited for the sun to come up before continuing.
Read about our fix of the problem here. This also eventually ended up melting some paths in the gauge cluster before we traced down the exact problem.
Overall the vehicle did very well. There was almost no squeaks and rattles, far less than expected for an older vehicle, and probably only the same amount it came from the factory with. The drivetrain ran perfectly. We recorded a gas mileage of 18 MPG average for the whole trip. The cruise control was intermittantly choosing not to work after a while. We will look at that when we have time. In the meanwhile it sort of works. When it wants to.
This vehicle had a remote start/keyless entry system installed by a previous owner, which adds nice convenience while being basically invisible and preserving the classic look since our Suburban came factory equipped with electric locks. The steering is adjusted properly and tracks well, and drives straight and smooth on the highway.
The next large task for our Suburban was to drive back up to Pennsylvania from Florida, and haul back a trailer load of tools, equipment, and household items. The trip north went fine, but as we reached our destination we realized the damage from the previous light circuit overload had worked its toll on the gauge cluster. The internal lights were not operating, making it difficult to drive at night.
We soldered a wire across the gap melted into the trace by the overload so we could get back home again with operating gauge cluster lights. We will fix this properly at a later date, and hopefully make some much needed updates to the gauges as well while still keeping a period and factory look. In the meantime, we hitched up the trailer and loaded up for the trip back south. We ended up with about 4,000 lbs gross trailer weight and a few hundred in the back of the truck.
It squats a lot when loaded, and we had balanced the tongue weight fairly well. The suspension does not seem to like towing and hauling. We will have to improve the suspension later. We headed out and made our way back south, uneventfully. The Suburban hauled wonderfully (if a little too light on the front), and the gas mileage dropped about 5 MPG, down to 13.
To make hauling and towing more stable, we added lift blocks for the rear springs after determining the spring sag when loaded was normal. The springs checked out ok, but raising the rear of the vehicle just slightly would make it level when hauling. A few loaded trailer runs verified this. Sadly we were in a hurry and did not document this.
Fixing the cruise control proved more difficult. The wiring for the switch where it passed through the steering column from the stalk was worn and was starting to fray into the copper, providing an intermittent effect. Read about our troubleshooting and repair of this system here.
On a quick local trip we parked beside a similar vintage suburban and jsut had to get a quick photo. It's nice to see these vehicles out and about being driven.
This tow dolly followed us home, and after some repair work seems to match our Suburban quite nicely!
We used it to bring home a 1978 El Camino, which is in need of some TLC. The Suburban towed the El Camino quite nicely and smoothly.
Although we had preserved the orignal headliner in our restoration, it was starting to show too much age. It had begun to sag in spots, and had a few small issues. It was time for a change. We pulled it out and stripped off the fabric and backing, down to the bare backing board.
We purchased headliner material and adhesive, and after carefully preparation applied the headliner to the bare board.
After allowing the adhesive to dry overnight, we trimmed the edges and cut out the holes as necessary
Then we installed both pieces of the new headliner and, and all the associated trim and ceiling fixtures.
We finally had some time for some maintenance on our suburban. For a while now it has been illuminating the 'Check Engine' light after about twenty minutes of driving. We took some time to pull the codes, and found a code 32 and 45.
The code 32 is 'EGR valve error'. We first examined the EGR valve, and immediately determined a vacuum hose was missing. We replaced this hose according to the hose routing diagram on the vehicle and hopefully this will resolve the issue.
The code 45 is 'Rich exhaust'. We aren't sure about this one right off the bat, so the first trial is to see if resolving the code 32 affects this one at all since that was an obvious problem. We will have to drive it for a while and see what happens.
Due to the global coronavirus issue, we haven't been doing much driving lately. But the air conditioning has started leaking down, and increasing faster also. We decided to take a look and troubleshoot that with all the extra time we have these days. Also we did notice the engine code '45' has not gone away, so we will have to look into that in detail at some point.
A detailed examination of the air conditioning system revealed a possible leak at the compressor shaft seal. There is oil and some dye present underneath the compressor snout. These Harrison R4 compressors are known to leak eventually at either the shaft seal or the case o-rings. The cylindrical compressor slides into a steel outer shell, and is only sealed with perimeter o-rings on each end.
We took the system apart, disassembled and re-sealed the compressor, and pressurized it again. We used a newer style double-lip shaft seal and r-134a compatible seals and o-rings. For the time being it seems to be holding pressure.
Since we haven't been driving much, we also opted to change out the aftermarket throttle cable someone had installed a long time ago. It is too short and thus bends too sharply, resulting in minor cable binding and a notchty pedal response. We installed the correct factory cable.
We still are doing limited driving in general thanks to coronavirus quarantining, and this resulted in a discovery about the gas tank. In our efforts to conserve money we ran the tank a lot lower than we usually allow and at about 1/16 tank according to the gauge we got stumbling and misfires on acceleration Which went away after getting fuel.
Apparently the tank baffling is not enough to keep gas centered under the pump when the tank is that low.
In investigating this stumbling (before determining the actual cause of low fuel), we pulled and replaced the aged and mismatched spark plugs which have been in the engine for quite some time. But this needed done anyhow.
We are still getting the code '45', so the cause was not the spark plugs. We have not had time to fully investigate this yet.
It appears we still have a very mild stumble under light acceleration. This may also be related to our code '45' we are still getting after a while of driving. Both of these issues seem to only happen when the accelerator is pressed lightly and when the engine is under load (i.e. not coasting or hard acceleration, or light acceleration down hill, or constant highway speed). The symptoms seem to indicate a small fuel delivery problem under certain conditions.
These GM TBI (Throttle Body Injection) systems are very simple in operation for a fuel injection system. The engine uses several sensors to indicate basically how much fuel the computer should deliver through the two injectors on the throttle body above the intake manifold.
The sensors are throttle position, absolute manifold pressure, vehicle speed, engine coolant temperature, ESC knock sensor, and an exhaust oxygen sensor, not counting emissions controls and sensors which can also have an effect.
In this case it seems like our prospective fuel delivery problem is most likely caused by the engine seeing an incorrect reading from somewhere under the conditions where the problem appears. We tested both the TPS (Throttle Position Sensor) and MAP (Manifold Absolute Pressure) sensor. Both tested ok with a multimeter. Both of these sensors control the fuel delivery based on engine throttle position and engine vacuum, which tell the computer how much air should be entering the engine and the vacuum of the intake manifold which indicates engine load.
The TPS can be tested by measuring pin resistance at the sensor, and observing this resistance as the throttle is opened and closed. If the reading does not move, moves erratically, or is not within proper limits then it is bad and should be replaced.
The MAP sensor can be tested by measuring output voltage at the sensor while vacuum is applied and released to the sensor. If the reading does not change, is not within limits or moves erratically then the sensor is bad.
Here is the MAP sensor, which is mounted on the intake on the passenger side of the throttle body atop the intake manifold:
Here is the test for the MAP sensor using a multimeter and a vacuum gun to selectively apply a vacuum to the sensor. With the sensor disconneced we used alligator clips to connect the two outside power connections and connected the multimeter to the center pin and ground.
The computer supplies a 5vdc reference voltage to the sensor, and reads a return voltage out through the center pin. This voltage varies with vacuum and tells the computer approximately how much manifold vacuum is present.
With both of these sensors confirmed working, we moved to the vacuum lines that can also have an effect on these sensors. We found a small pinhole in the supply line for the MAP sensor.
We replaced this line and hopefully this will help, but it doesn't seem like this is enough to cause our particular issues, especially as the hole is close enough to the end it might be past the end of the connection seal anyhow. Test driving the vehicle confirmed the issue still exists.
Next up on our list is the coolant temperature sensor. This sensor also uses 5vdc to return a reference voltage through the variable resistance of the sensor based on coolant temperature. Seperate from the gauge sender, this sensor tells the ECM engine temperature range so that it can adjust fuel accordingly as a cold engine will generally need a richer mixture.
Just like the previous sensors, there are two testing methods: voltage or resistance. For testing output voltage everything must be connected and the yellow wire must be accessible for a meter reading for +dcv.
In this case the resistance reading is much easier since we can just connect the meter probes to the two sensor terminals and take readings under different temperatures. The proper resistance readings for temperature are here:
Coolant sensor approximate resistance specifications:
177 ohms @ 212 deg. F. or 100 deg. C.
241 ohms @ 194 deg. F. or 90 deg. C.
332 ohms @ 176 deg. F. or 80 deg. C.
467 ohms @ 158 deg. F. or 70 deg. C.
667 ohms @ 140 deg. F. or 60 deg. C.
973 ohms @ 122 deg. F. or 50 deg. C.
1188 ohms @ 113 deg. F. or45 deg. C.
1459 ohms @ 104 deg. F. or 40 deg. C.
1802 ohms @ 95 deg. F. or 35 deg. C.
2238 ohms @ 86 deg. F. or 30 deg. C.
2796 ohms @ 77 deg. F. or 25 deg. C.
3520 ohms @ 68 deg. F. or 20 deg. C.
4450 ohms @ 59 deg. F. or 15 deg. C.
5670 ohms @ 50 deg. F. or 10 deg. C.
7280 ohms @ 41 deg. F. or 5 deg. C.
9420 ohms @ 32 deg. F. or 0 deg. C.
12300 ohms @ 23 deg. F. or -5 deg. C.
16180 ohms @ 14 deg. F. or -10 deg. C.
21450 ohms @ 5 deg. F. or -15 deg. C.
28680 ohms @ -4 deg. F. or -20 deg. C.
52700 ohms @ -22 deg. F. or -30 deg. C.
100700 ohms @ -40 deg. F. or - 40 deg. C.
Performing this test on a hot engine and taking meter readings as it cooled as well as temperature readings with a laser thermometer, we found sensor output to be very erratic and sometimes not in the correct range, often indicating too hot. We replaced the sensor after the engine was completely cooled.
We will have to test drive the vehicle for a while and get feedback before we can say for sure whether our problem is yet fixed. If not, at least we are narrowing down the list of possibilities.
With the stumbling problem still not solved (and getting worse every day), we turned again to further possibilities. We have eliminated pretty much all fuel and air possibilities, so only spark remains.
The ignition modules on these distributors can go bad, causing hard starts and poor running due to incorrect timing. Although our truck is exhibiting only partial symptoms of this it still could be a possibility. Also the cap and rotor could wear considerably, causing low spark voltage. Since both involve removing the distributor cap we opted to replace cap, rotor, and ignition module all at once.
Removing the distributor cap confirmed our suspicions: the carbon button on the cap center is very worn, the cap contacts inside are corroded, and the rotor contacts are worn and corroded. The rotor is so old that the metal spring clip that holds it in place rusted to the top of the distributor shaft and had to be pried loose. We replaced both the cap and rotor.
Since everything was apart, we replaced the ignition module being careful to apply heat-sink grease between the distributor casing and module so the new unit does not overheat and burn out.
We drove this vehicle from Florida to New York, and it seems the issue is still not solved though. Our best guess at this point is plug wires and/or coil. We will have to examine this in the future. Also we managed to get a flat tire necessitating the use of the spare, which proved to be in good shape except low on air(forgot to check it lately, oops).
This long trip and our recent resurrection of this 1987 Suburban has given us a great comparison of a very similar vehicle in both age and quality. That vehicle had a tailgate rather than barn doors, and for purposes of rear visibility while driving that vehicle far exceeded the wide middle divider in the barn doors.
That truck did not also have the complete towing package that this one has, with the heavy-duty oil cooling. Overall the coolers add a nice stability to the drivetrain temperature that the 1987 Suburban does not have. On our daily driver 1988 the temperature needle stays rock-steady after the initial peak and thermostat opening, while on the 1987 with no extra coolers it cycles up and down somewhat.
We finally had some time to re-examine the stumbling issue. With few options left, we replaced the plug wires and coil. Just to make sure, we fine-tuned the timing with the computer timing adjustment unplugged. The base timing was only off by a few degrees, so we adjusted it back to zero.
It appears the issue is finally solved! All stumbling and misfires are gone. After our examination of parts taken off, we determined one wire was completely shot where the fitting crimped to the wire end. The wire had infinite resistance on our meter and thus was not functioning at all.
Hopefully this may resolve our intermittent engine rich code.