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1986 and 1989 S10 Blazers
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EdG
Novice
Jan 2, 2007, 10:19 PM
Post #1 of 7
(7252 views)
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1986 and 1989 S10 Blazers
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1986 S10 Blazer, delivered Feb 24, 1986, 2.8L 5 speed manual, 4X4, 136,000 miles. Build sheet and dealer ordered option documents available if needed.
Shortly after delivery fast idle occurred. Repaired by dealer without explanation. Power door lock serviced per recall. Routine maintenance performed including ball joint, CV joint seals. Transmission replaced in 1999-cluster gear and main bearing failure. Replacement transmission obtained from salvage yard because more cost effective than trying to repair original with parts from Chevrolet. Car functioned well until summer of 2001 when it developed surging—at idle surged from 2500 to 3500 rpm. Just noticed that it was happening-there was no spectacular event that started it. Car drove well as long as selected gear kept the tach over 3000 rpm and not in too much city traffic. Live in country so majority of driving at 45-55 mph. MPG reduced from 20 to 15. At the time, there were no codes (there have never been any codes). I couldn’t find anything so had it checked by mechanic who does our inspections. He replaced O2 sensor, distributor cap and rotor, spark plugs, spark plug wires, thermostat, and air filter. Surging still present and mechanic had no explanation. In addition, the gauges were fluctuating so I tried to make sure that all grounds were competent. Taken out of service fall of 2001 (spent winter in AZ). The car was not driven the following summer and it ultimately remained out of service until August 2006. Decided to winter in PA this year and wanted the 4X4 vehicle again.
I have been fixing my own cars for over 50 years and since I have both the Helm service and unit repair manuals for 1986 Blazer, I figured it would not be too difficult. LOL. In order to get it going to see what had to be done, had to fix a lot of things. It needed a cat converter/muffler exhaust pipe, a muffler, and a tailpipe. Front brakes were locked-this required replacing both flexible hydraulic hoses. Also had to replace brake lines, which had rusted out. Alternator would not charge. Discovered the front frame on a 1986 CS alternator was unique to that year so had to rebuild a replacement alternator using the front frame of the original. Now the car was driveable. The oil pressure gauge was jumping wildly from top to bottom and would get somewhat better when engine reached operating temp but it repeated the same thing each cold start. I thought it was oil pressure sensor or its wiring. Original had been replaced in mid 1990s because of a leak. Subsequently, with regular use, oil pressure gauge and sending unit problem has resolved and they are functioning normally. However still idling at 3000 and still surging. In addition, it has episodes of hesitation and lurching-my wife describes as riding a bucking bronco. Still no codes.
Many acquaintances/friends who are mechanics and/or automotive engineers said it could be a vacuum leak. Tested each circuit and even plugged all vacuum outlets on throttle body and induction system. High idle remaines. Mechanic at dealership suggested that some vacuum leaks were caused by a leaking TBI/intake manifold gasket leak so we replaced that gasket. No change. Because of the gauge fluctuations, again checked all grounds, following suggestion in manual about intermittents, tried to confirm competence of all wiring and connectors. I have wired several vehicles, including a bus, where I had to reconstruct a wiring harness, so I felt quite comfortable checking the wiring. Installed known good IAP, TPS, MAP sensors, EGR valve, EGR vacuum switch and ECU. As I suspected, none of those helped. Even though I checked basic timing in 2001, I rechecked now and it appears to be normal. According to the techniques in the manual, I checked basic (non-computer assisted/IAP) idle. It appeared to be normal. With 130,00 miles, I was concerned that fuel filter could be clogged. It was clogged but in process of replacing, fuel line broke at the fitting to the filter where it was badly corroded so had to replace the fuel line. I was hoping the clogged filter was the source of the problem, but it wasn’t. Every once in a while (every 2-3 weeks) for a few seconds to a minute, idle slows to 1500 rpm but then right back up. Occasionally, the motor appears to run better when first started. There are periods of time when it does not surge or buck. It is driveable, especially out of traffic, but mpg remains around 15. I have not been able to find any reason for the times when it is better. I have always been suspicious of the wiring but I have not been able to find any wires or connectors that I can manipulate to cause or cure the high rpm condition.
The fun continues. Several years ago, I bought an 89 S10 Blazer, 4.3 automatic 4X4, from my brother to use for plowing. That never happened. Since I was having so much fun with the 86, I thought I would try the 89. It starts, but when I release the starter switch it stalls. None of the gauges work. The fuel reads full (which it isn’t) the oil pressure starts at 0 and if the engine starts at all, goes to the top and stays there. The volt meter reads low and it has not run long enough to know about the temp gauge. The CS alternator does not charge. To make matters worse, I do not have a Helms manual for this 89. The wiring in the 89 appears to be different from the 86 and I don’t know if that is because of the 4.3 L engine (vs the 2.8) or there are just a lot of wiring changes. I would have expected that the dashboard wiring would be very similar but it does not appear to be. I thought I would look for the ground wire for the instruments and dash-similar to the 86- but I can’t find it and the generic manuals I have seen don’t show where the grounds are.
Does anybody have any documentation for ground wire locations for the 89? Are there any conditions that might cause the gauge malfunction? I have confirmed that the fusible links are OK and I used an alternative wire on the run circuit in an effort to rule out an ignition switch problem. Are there other reasons why it will only run while the switch is in the start position? This vehicle was functioning normally the last time it was driven -also in 2001.
I have never had the experience of not being able to fix a vehicle like these two and I am nearly exhausted. I will greatly appreciate any advice, suggestions, tips, or leads to information................Ed
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DanD
Veteran
/ Moderator
Jan 3, 2007, 5:22 AM
Post #2 of 7
(7243 views)
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Re: 1986 and 1989 S10 Blazers
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Man you weren’t kidding about a long first post. LOL
But that’s good at least we know what you’ve done and tried and hopefully we can go forward with this repair and not have to back track too much.
One of the first things I would like to know is some of the scan data; as in IAC (idle air control) counts, does PCM (power-train control module) have control of system, is the system in closed loop, input sensors do they/are they sending “normal” signals?
Scanning a PCM is more then just checking for codes; for example if there is a power steering pressure switch that has gone bad and signaling the PCM that there is high power steering system pressure. The PCM will increase idle to hopefully prevent a stall during parking lot maneuvers.
A normal IAC count is around 12 to 16 counts at idle after the engine reaches normal operating temperature. So if I see a count of 30, 40 or 60 I’m going to look for reason that the PCM thinks it has to raise idle. Again a malfunctioning pressure switch, high signal from MAP; which would cause the PCM to think there is excessive load (low vacuum) on the engine causing the PCM to increase idle to compensate.
Or if the IAC counts were in the basement and showing 0 (zero) counts I would be looking for vacuum leaks, stuck/binding throttle plates and or cable, holding throttle open.
TPS (throttle position sensor) should be approximately ½ (.5) of a volt; yes you can measure that with a multi-meter by back probing the signal return wire but a scanner will give you the PCM’s interpretation of this input.
I could go on about scan data and I’m sorry if you already knew this but so many people think codes are the answer to every running issue a vehicle has.
Reading scan data and the reaction between inputs and outputs to and from the PCM will usually tell you whether the problem is electrical or mechanical.
After saying all that and with your description of this problem, my gut feeling is some form of vacuum leak.
I know you said that you’ve already replaced the TBI gasket but the intakes to cylinder head gasket were also bad for vacuum leaks. They can be difficult to diagnose because the intake would be drawing air from inside the lifter valley. If this was the case and the leak is bad enough you maybe able to confirm it by removing the PCV valve from the valve cover and plugging the hole. Run the engine at idle and cap off the fresh air inlet tube from the air breather to the other valve cover with your thumb. You should feel some form of positive pressure coming from and out of the tube. If you have vacuum then you can be pretty confident that the intake gasket is sucking air.
As for the 89 I’ll have to look to see what I have for splice or ground connection locations. The wiring diagrams for these were hit and miss if they supplied this info.
Dan.
Canadian "EH"
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EdG
Novice
Jan 3, 2007, 8:28 PM
Post #3 of 7
(7235 views)
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Re: 1986 and 1989 S10 Blazers
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Thank you for the reply.
I checked the fresh air inlet tube as you instructed. There is no vacuum and could detect only a small amount of air going in.
I do not have a scan tool and have been using only the ALCL connector to get codes. When I talked with the Chevrolet dealer a couple months ago, he said he would do a scan—that was when he thought it was a 1996. When he realized it was a 1986, he said there was nothing he could do with it. In retrospect, I don’t know whether his loss of interest was because he didn’t have the right scanner or for some other reason. He did say that it sounded like a vacuum leak and suggested that it might be the throttle body gasket. At the time, I must admit that I thought the 1986 system was so unsophisticated that a scanner would only give the same codes I was getting from the ALCL jumpers. After your response I found the description of the scanner tool in the manual and see that it describes all the parameters you mention. I appreciate the education.
We have looked on-line to see if I can buy an OBD I scan tool but am unable to find anything. I found one device but it looks like only a code reader. I called local auto parts stores as well as PartsAmerica and no one has one. Do you have any suggestions about where I might get access to a correct scanner-either for purchase or temporary use?
I have a scanning tool for an Allison HD transmission from a bus that is from the right time period. It says it can identify hard and soft codes, identify PROM ID, identify throttle counts, oil temp, input voltage, reference voltage and various other features. It has a 12 button key pad as well as a digital display. I believe it was made specifically for Allison and won’t work as a generic scanner and do not know what might happen if I connect an improper device.
When I go into Field Service Mode, it starts off blinking rapidly (open loop) and within 30 seconds switches to blinking slowly (closed loop). When the vehicle is surging, it appears to be running rich. The light is on longer than off. When a non-surging event happens, it appears to be running lean- off time greater than on. It never throws a code so I assumed the computer was identifying normal variations that were not abnormal enough to initiate a code.
Thanks…..Ed
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EdG
Novice
Jan 4, 2007, 10:11 PM
Post #5 of 7
(7223 views)
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Re: 1986 and 1989 S10 Blazers
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Found a scanner on eBay. It is scheduled for delivery next Monday. Will run a scan asap and report findings.
Need to correct my previous post. I believe a little air was coming out the inlet tube-misstated that it was going in. My conclusion was that there was not a vacuum condition in the crankcase. Sorry for the confusion. When the scanner gets here I will plug the PCV opening with a rubber plug and put a vacuum pressure gauge on the inlet tube. That way we will get an absolute reading..........Ed
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EdG
Novice
Jan 7, 2007, 7:15 PM
Post #6 of 7
(7216 views)
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Re: 1986 and 1989 S10 Blazers
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Scanner arrived late Saturday instead of Monday. Below are results from three scans. The first was done with the engine not running and the other two with it running. There is not much explanation in either the Chevrolet manual or the scanner documentation regarding normal values and I am still trying to decipher some of the findings. For instance you will see that battery voltage is 0, 0.5 and 1.4 respectively, with a maximum of 0.3 to 1.5. Also note that “Battery High” and Battery Low” both say “No”. I don’t understand-I expected it to be 12-14. I set the TPS at 0.450 with the throttle body unit in idle position so I am surprised at the scanned voltage. I am wondering if there is a problem with the grounds to the ECM. I think the 12V supply is intact. Re O2 sensor--in addition to what the report shows, I saw values from upper 30s to 818 mV in monitor mode. On the scans where the engine was running, A/C is Requested, but the switch was not on.
This is a 5 speed manual trans so I don’t understand Park/neutral detected.
This is my first experience with a scanner so I hope you will comment on what you see and clarify all the stuff I don’t “get”.
Have attached schematic of ECM and sensors in hopes that will help figure this out.
Vehicle Scan Report
Data Downloaded from Scanner: 01/07/2007 02:44 PM
Comments
86 S10 prim
Trouble Codes
<none found>
Pending Codes
<none found>
Operational Data
## Parameter Name Value Units (if applicable)
1 PROM ID 8061.00
2 Idle Air Mtr Pos 100.00 steps
3 Coolant Temp 41.00 °F
4 Vehicle Speed 0.00 MPH
5 MAP Sensor 4.66 Volts
6 Engine RPM 0.00 RPM
7 Throttle Sensor 2.72 Volts
8 Integrator 128.00
9 Oxygen Sensor 462.00 mVolts
10 Battery Voltage 0.00 Volts
11 Block Learn 128.00
12 O2 Cross Counts 0.00
13 Battery Voltage High : No
14 Clear Flood Mode Off
15 Learn Control Disabled
16 Battery Voltage Low : No
17 Rich Lean Flag Lean
18 Loop Status Open
19 A/C Not Requested
20 Engine Cranking No
21 Park/Neutral Not Detected
22 TCC Status Not Locked
23 A/C Clutch Disabled
Scan Report Page 1 of 1
Vehicle Scan Report
Data Downloaded from Scanner: 01/07/2007 02:55 PM
Trouble Codes
<none found>
Pending Codes
<none found>
Operational Data
## Parameter Name Value Units (if applicable)
1 PROM ID 8061.00
2 Idle Air Mtr Pos 120.00 steps
3 Coolant Temp 186.80 °F
4 Vehicle Speed 0.00 MPH
5 MAP Sensor 1.07 Volts
6 Engine RPM 2550.00 RPM
7 Throttle Sensor 2.37 Volts
8 Integrator 128.00
9 Oxygen Sensor 462.00 mVolts
10 Battery Voltage 0.50 Volts
11 Block Learn 128.00
12 O2 Cross Counts 142.00
13 Battery Voltage High : No
14 Clear Flood Mode Off
15 Learn Control Disabled
16 Battery Voltage Low : No
17 Rich Lean Flag Lean
18 Loop Status Open
19 A/C Requested
20 Engine Cranking Yes
21 Park/Neutral Detected
22 TCC Status Not Locked
23 A/C Clutch Disabled
Scan Report Page 1 of 1
Vehicle Scan Report
Data Downloaded from Scanner: 01/07/2007 04:51 PM
Trouble Codes
<none found> Pending Codes
<none found> Operational Data
## Parameter Name Value Units (if applicable)
1 PROM ID 8061.00
2 Idle Air Mtr Pos 120.00 steps
3 Coolant Temp 123.80 °F
4 Vehicle Speed 0.00 MPH
5 MAP Sensor 1.03 Volts
6 Engine RPM 2525.00 RPM
7 Throttle Sensor 2.52 Volts
8 Integrator 128.00
9 Oxygen Sensor 457.00 mVolts
10 Battery Voltage 1.40 Volts
11 Block Learn 128.00
12 O2 Cross Counts 182.00
13 Battery Voltage High : No
14 Clear Flood Mode Off
15 Learn Control Disabled
16 Battery Voltage Low : No
17 Rich Lean Flag Lean
18 Loop Status Open
19 A/C Requested
20 Engine Cranking Yes
21 Park/Neutral Detected
22 TCC Status Not Locked
23 A/C Clutch Disabled
Scan Report Page 1 of 1
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Attachments:
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86 S10 p1.pdf
(34.0 KB)
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86 S10 p2.pdf
(35.0 KB)
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86 S10 p3.pdf
(38.5 KB)
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EdG
Novice
Jan 7, 2007, 11:33 PM
Post #7 of 7
(7215 views)
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Re: 1986 and 1989 S10 Blazers
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Readjusted the TPS--- I found that it really was out of adjustment. I may have tried adjusting it without a voltmeter trying to get the smoothest idle. At any rate, it was nowhere near the 0.45 setting that I had previously done. In addition, I noticed replacement ground wires that I had put in several years ago were in close proximity to the replacement spark plug wires, which are longer than the original. I started the engine and it was idling around 1500 instead of 2500 and the TPS voltage was 0.47. I reset the computer by removing the battery ground and did another scan-results below. I am interested in your interpretation of what went on because the high idle and surging occurred before I replaced the spark plug wires and grounds. I am now wondering if the original problem may have been a clogged fuel filter and that it would have gotten better except that in the process of re-grounding, I probably let ground wires get too close to spark plug wires on the left side of the motor at the rear. I think the ground wires to the computer may have picked up inductive interference from the spark plug wires, which may have contaminated the control signals to the IAC and other sensors. Do you think that is possible?
Will be driving 100 miles tomorrow so I will see how it performs. I keep hoping I have found the answer but I don’t want to get too excited.
Vehicle Scan Report
Data Downloaded from Scanner: 01/07/2007 10:41 PM
Trouble Codes
<none found>
Pending Codes
<none found>
Operational Data
## Parameter Name Value Units (if applicable)
1 PROM ID 8061.00
2 Idle Air Mtr Pos 14.00 steps
3 Coolant Temp 186.80 °F
4 Vehicle Speed 0.00 MPH
5 MAP Sensor 1.58 Volts
6 Engine RPM 800.00 RPM
7 Throttle Sensor 0.47 Volts
8 Integrator 128.00
9 Oxygen Sensor 638.00 mVolts
10 Battery Voltage 0.20 Volts
11 Block Learn 111.00
12 O2 Cross Counts 113.00
13 Battery Voltage High : No
14 Clear Flood Mode On
15 Learn Control Disabled
16 Battery Voltage Low : No
17 Rich Lean Flag Rich
18 Loop Status Open
19 A/C Requested
20 Engine Cranking Yes
21 Park/Neutral Detected
22 TCC Status Not Locked
23 A/C Clutch Disabled
Scan Report Page 1 of 1
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