CK5
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**Resolved** After replacing the O2 sensor and other things on my 1989 K5 its lugging and idling poorly
- Thread starter clutch2k3
- Start date
How does the ECM get the vehicle's speed on my 1989 K5 4WD Blazer with 350 TBI, 700R4, NP transfer case? All I see on my truck is an old-school thick, grey speedo cable connected to the tail of the transfer case going off towards the firewall. Even after installing 4.10's (33" tires) the speedometer in the dash is 5 MPH faster than GPS. I've seen a few posts elsewhere saying that the VSS directly affects TCC lockup. I've been firing-off the parts cannon and plugging vacuum lines but it's still surging/lugging during TCC lockup.
I never knew that. Thank you
The TBI setup doesn't have VSS scaling in the ECM like newer vehicles. If you have the DRAC module under the dash, it can be reconfigured: https://www.tradecraftspecialties.com/DRACmodule#Topic1
As long as you have a speedometer cable, you can also calibrate mechanically by swapping the driven gear in the transfer case. If you can't get the right number of teeth, then you swap the drive gear, which is more difficult (and those gears are hard to find in alternate tooth counts). The little housing on the transfer case gets clocked in different orientations based on driven gear tooth counts (because they are different diameters). I believe that more than one gear holder exists for different tooth counts. Since you have to have an integer # of teeth and not every number is available, you may not get it exactly right, but then again, almost every car has error in the speedometer.
Stock seems to come and go between different suppliers, but here's an example. https://www.classictransmissionsolutions.com/gm-np208-4x4/. Keep in mind while shopping that all of the parts are different between GM and Jeep/Dodge. I had the best luck asking guys at local drivetrain shops, but there are fewer people working on this old stuff these days.
It was originally for the cruise control, but when EFI started, they kept the same speedo, speedo cable, etc. and then the electronic signal was used for both cruise control and the ECM. The speedometer reading is a balance between a return spring and the magnetic pull of steel passing magnets. As the cable speeds up, you get a pull more often, bringing the needle higher. The optical eye is looking at this spinning steel piece, so you get 2 pulses for every revolution of the speedometer cable. You'll see this on the back of the cluster:
could I replace the green box optical sensor with a DRAC?
You may be thinking of it wrong. If that was true, you could park the truck and the speedometer would still be at 5. If you mean at 55MPH (for example), then it's off by ~9%, which is how much you would modify the multiplier in the DRAC. So if you went 110MPH it would read 10MPH fast (not that I recommend this experiment
).
For what purpose? It wouldn't fix the speedometer being off, and the ECM isn't going to care much at all that the speed signal is 9% off.
Since I got you here, my 98 needs correction after the bigger tires, is it programmable or does it still use a DRAC?
Understood, my wording was poorYou may be thinking of it wrong. If that was true, you could park the truck and the speedometer would still be at 5. If you mean at 55MPH (for example), then it's off by ~9%, which is how much you would modify the multiplier in the DRAC. So if you went 110MPH it would read 10MPH fast (not that I recommend this experiment
I'm chasing down an elusive problem during TCC lockup and fwict VSS affects TCC lockup. I'd like to eliminate this as the potential source of the problem. I don't care about the speedometer. I'm open to any other ideas.
no 98 has VSS and ecm controlled speedo.
You still have working cruise control? I *believe* that was always set at 25mph minimum engagement threshold. If there is a problem with VSS reading way too slow or way too fast, you will either be able to engage it significantly before 25mph, or conversely until significantly after 25mph.
Winaldl or the like will let you check what the ECM is seeing for MPH to verify VSS operation.
It would be very unlikely for VSS to be malfunctioning without the speedometer acting weird too, since both are "driven" with the same speedometer cable. But cruise control working properly will essentially eliminate VSS as a problem.
The only way I could see VSS affecting TCC and nothing else is if whatever wiring controls TCC, after the VSS buffer, is damaged.
In the log shown on the 1st page, there is a VSS being logged. It also shows the converter being locked and unlocked and the results are noticed, so all of that is working right. I can't see the VSS being "wrong" other than the multiplier error in the DRAC. It's worth considering that in any old vehicle you don't really know what all has been done to it, but since the vehicle used to run OK it seems unlikely that this small error in VSS is causing night and day bad driving.
What about the TPS? If the engine is off, key on, foot to the floor, what does it read?
Looking back, I'm also wishing for a better description of "lugging". Is it just that the engine is out of the powerband, or is it really misfiring?
I finally got the logs to work.
Where's the timing portion of the log? I see knock building at Time 58.2 due to the lean condition which to me says its not getting enough fuel to keep it out of knock under load, and you are *probably* seeing timing retard when that happens. The TCC ("1" when commanded) isn't locked at that point according to the log. When it does lock again, it goes lean and knocks, but I would expect that results from the increased load on the engine from the TCC, but lack of corresponding fuel fast enough to meet the load.
Same thing is repeated at about 172.3, vehicle is accelerating based on RPM/MPH, TPS has increased, yet INT has gone lean again, and knock starts at 173. This time TCC is engaged.
At 275.8 TCC unlocks but INT again goes lean under load, and knock occurs.
The conditions that put an engine into knock start before knock occurs, it seems based on that log that the engine is lean under load, regardless of TCC status. Would need to see the timing log to compare to knock counts to see if it's pulling timing when it knocks, but that is the strategy, and will drastically reduce power.
I'm not an automatic guy, but hopefully I'm not too far off base here.
No DRAC stock in anything but the '90-91's, so shouldn't be an issue here. Vehicle speed seems ok to me (as in reporting consistently), can easily figure out how far off it is with tire size, gear ratio, and transmission gear ratio with any of the multitude of online calculators. Already have the MPH and RPM that the computer is displaying, I doubt there is a major issue here with that.
Where's the timing portion of the log? I see knock building at Time 58.2 due to the lean condition which to me says its not getting enough fuel to keep it out of knock under load, and you are *probably* seeing timing retard when that happens. The TCC ("1" when commanded) isn't locked at that point according to the log. When it does lock again, it goes lean and knocks, but I would expect that results from the increased load on the engine from the TCC, but lack of corresponding fuel fast enough to meet the load.
| Time | SENSOR:SPEED | SENSOR:RPM | SENSOR:TPS | SENSOR:INT | SENSOR:Knock counter | MCU2IO:TCC Locked |
57 | 17 | 1825 | 25.8 | 128 | 2 | 0 |
58.2 | 19 | 2275 | 32.7 | 138 | 2 | 0 |
59.4 | 23 | 2375 | 32.7 | 141 | 3 | 0 |
60.5 | 26 | 2400 | 33.2 | 137 | 3 | 0 |
61.7 | 29 | 2500 | 33.2 | 133 | 4 | 0 |
62.9 | 32 | 2550 | 32.7 | 126 | 4 | 0 |
64.1 | 34 | 2575 | 32.7 | 127 | 4 | 0 |
65.2 | 36 | 2325 | 32.7 | 128 | 5 | 0 |
66.4 | 38 | 2375 | 32.2 | 127 | 5 | 0 |
67.6 | 40 | 2300 | 28.5 | 123 | 5 | 0 |
68.8 | 41 | 2200 | 24.2 | 122 | 5 | 0 |
69.9 | 42 | 2200 | 24.8 | 123 | 5 | 0 |
71.1 | 43 | 2250 | 24.8 | 127 | 5 | 0 |
72.3 | 44 | 2250 | 24.8 | 129 | 5 | 0 |
73.5 | 46 | 1800 | 24.8 | 129 | 6 | 1 |
74.6 | 46 | 1825 | 24.8 | 135 | 7 | 1 |
75.8 | 47 | 1875 | 23.2 | 131 | 9 | 1 |
77 | 48 | 1350 | 22.1 | 131 | 12 | 1 |
78.2 | 48 | 1350 | 19 | 124 | 12 | 1 |
Same thing is repeated at about 172.3, vehicle is accelerating based on RPM/MPH, TPS has increased, yet INT has gone lean again, and knock starts at 173. This time TCC is engaged.
| Time | SENSOR:SPEED | SENSOR:RPM | SENSOR:TPS | SENSOR:INT | SENSOR:Knock counter | MCU2IO:TCC Locked |
169.9 | 38 | 2150 | 23.2 | 127 | 12 | 0 |
171.1 | 40 | 2125 | 22.1 | 127 | 12 | 0 |
172.3 | 41 | 2100 | 21.1 | 126 | 12 | 1 |
173.4 | 41 | 1650 | 20.5 | 132 | 13 | 1 |
174.6 | 42 | 1675 | 20.5 | 133 | 14 | 1 |
175.8 | 44 | 1750 | 19 | 130 | 15 | 1 |
177 | 44 | 1750 | 17.4 | 125 | 15 | 1 |
178.2 | 45 | 1750 | 14.7 | 125 | 15 | 1 |
At 275.8 TCC unlocks but INT again goes lean under load, and knock occurs.
271.1 | 32 | 1350 | 3.6 | 122 | 15 | 1 |
272.2 | 32 | 1300 | 8.9 | 126 | 15 | 1 |
273.4 | 32 | 1300 | 8.4 | 132 | 15 | 1 |
274.6 | 33 | 1325 | 8.4 | 133 | 15 | 1 |
275.8 | 33 | 1325 | 0.5 | 131 | 15 | 0 |
276.9 | 34 | 2250 | 30.1 | 126 | 16 | 0 |
278.1 | 36 | 2300 | 30.1 | 129 | 16 | 0 |
279.3 | 39 | 2325 | 30.1 | 133 | 16 | 0 |
280.5 | 40 | 2350 | 30.1 | 131 | 17 | 0 |
281.6 | 42 | 2350 | 30.1 | 131 | 17 | 0 |
The conditions that put an engine into knock start before knock occurs, it seems based on that log that the engine is lean under load, regardless of TCC status. Would need to see the timing log to compare to knock counts to see if it's pulling timing when it knocks, but that is the strategy, and will drastically reduce power.
I'm not an automatic guy, but hopefully I'm not too far off base here.
No DRAC stock in anything but the '90-91's, so shouldn't be an issue here. Vehicle speed seems ok to me (as in reporting consistently), can easily figure out how far off it is with tire size, gear ratio, and transmission gear ratio with any of the multitude of online calculators. Already have the MPH and RPM that the computer is displaying, I doubt there is a major issue here with that.
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First off, thanks to everybody thats looked at this and commented, I truely appreciate it. We planned on using the K5 for family camping trips by this time of the year but this issue has thrown those plans out the window.
I've replaced the rear gears and the issue persists and now I beleive the TCC itself must be eliminated as the potential source of the problem - I plan on having a shop replace the torque convertor and TCC lock up solenoid.
Responses to comments:
My cruise control (mostly) still works. I don't belive the speedo gears are way off. From my calculations my speedo gears are for 3.08 gears w//28" tires and now there's 4.10 gears with 33" tires.
I have been using Winaldl to check what MPH the ECM is seeing - it lines up with 4.10/33" through a 3.08/28" speedo
The speedometer and ECM are in aggreement on MPH
I probably made it sound like I think there's "a problem" with the VSS, but I just know the speedo gearing doesn't match the current gears/tires
AFAIK my truck does not have a DRAC, it only has an optical sensor (green box). AFAIK DRACs are only applicable to electronic VSS's which my truck does not have.
TPS has been set, set again and then set agian. I've lost count of the number of times I've performed the minimum idle air procedure, set the TPS and verified TPS is working OK. The minimum idle air procedure has been printed out, laminated and stored in the center console (I'm not joking).
the truck feels like its going over a rumble strip **only** during TCC Lock up. IDK if that should be called "lugging", "surging, "misfiring", etc.
I installed a TCC lockup override switch and I've been turning the "rumble strip effect" on/off with the flick of a switch.
AFAIK ign timing, fuel pressure and duty cycle are not logged :-(
IMO 10's of knock events spread out over a few seconds wouldn't feel like the truck is going over a rumble strip, but I really don;t have that much experience here. I assumed at least 10's of knock events per second would be required to imitate a rumble strip and I've data logged while the rumble strip effect has gone on for minutes at a time.
The fuel pump, Delphi FE0115 w/max 12-PSI, was installed about a year ago. If its a fuel delivery issue then the fuel delivery issue is only present during TCC lock up.
I've replaced the rear gears and the issue persists and now I beleive the TCC itself must be eliminated as the potential source of the problem - I plan on having a shop replace the torque convertor and TCC lock up solenoid.
Responses to comments:
My cruise control (mostly) still works. I don't belive the speedo gears are way off. From my calculations my speedo gears are for 3.08 gears w//28" tires and now there's 4.10 gears with 33" tires.
I have been using Winaldl to check what MPH the ECM is seeing - it lines up with 4.10/33" through a 3.08/28" speedo
The speedometer and ECM are in aggreement on MPH
I probably made it sound like I think there's "a problem" with the VSS, but I just know the speedo gearing doesn't match the current gears/tires
AFAIK my truck does not have a DRAC, it only has an optical sensor (green box). AFAIK DRACs are only applicable to electronic VSS's which my truck does not have.
TPS has been set, set again and then set agian. I've lost count of the number of times I've performed the minimum idle air procedure, set the TPS and verified TPS is working OK. The minimum idle air procedure has been printed out, laminated and stored in the center console (I'm not joking).
the truck feels like its going over a rumble strip **only** during TCC Lock up. IDK if that should be called "lugging", "surging, "misfiring", etc.
I installed a TCC lockup override switch and I've been turning the "rumble strip effect" on/off with the flick of a switch.
AFAIK ign timing, fuel pressure and duty cycle are not logged :-(
IMO 10's of knock events spread out over a few seconds wouldn't feel like the truck is going over a rumble strip, but I really don;t have that much experience here. I assumed at least 10's of knock events per second would be required to imitate a rumble strip and I've data logged while the rumble strip effect has gone on for minutes at a time.
The fuel pump, Delphi FE0115 w/max 12-PSI, was installed about a year ago. If its a fuel delivery issue then the fuel delivery issue is only present during TCC lock up.
Actually it's the same system from 1982 for cruise (VSS buffer using an optical eye) and adapted to TBI (and probably CCC) through 1989.
The 1990-1991 setups actually didnt change much signal-wise except the input (VSS on the t-case) and the speedo driver. The pulses that cruise, ECM, and I assume ABS receive are the same as the earlier mechanical/optical VSS setup.
