Persistent no start--at the end of my rope!

[Ecomike]

This is somewhere in the FSM or a bulletin I found a while back:

1988 Jeep Cherokee
GENERAL INFORMATION
Computer Relearn Procedures
All Models
* PLEASE READ THIS FIRST *
The following general procedures are to be used if
driveability problems are encountered after power loss or battery has
been disconnected. These procedures may provide an aid in eliminating
these problems.
To reduce the possibility of complaints, after any service
which requires battery power to be disconnected, vehicle should be
road tested.
COMPUTER RELEARN PROCEDURES
Vehicles equipped with engine or transmission computers may
require a relearn procedure after vehicle battery is disconnected.
Many vehicle computers memorize and store vehicle operation patterns
for optimum driveability and performance. When vehicle battery is
disconnected, this memory is lost. The computer will use default data
until new data from each key start is stored. As computer memorizes
vehicle operation for each new key start, driveability is restored.
Vehicle computers may memorize vehicles operation patterns for 40 of
more key starts.
Customers often complain of driveability problems during
relearn stage because vehicle acts differently then before being
serviced. Depending on type and make of vehicle and how it is
equipped, the following complaints (driveability problems) may exist:
* Harsh Or Poor Shift Quality
* Rough Or Unstable Idle
* Hesitation Or Stumble
* Rich Or Lean Running
* Poor Fuel Mileage
These symptoms and complaints should disappear after a number
of drive cycles have been memorized. To reduce the possibility of
complaints, after any service which requires battery power to be
disconnected, vehicle should be road tested. If a specific relearn
procedure is not available, the following procedure may be used:
Automatic Transmission
* Set parking brake, start engine in "P" or "N" position.
Warm-up vehicle to normal operating temperature or until
cooling fan cycles.
* Allow vehicle to idle for one minute in "N" position. Select
"D" and allow engine to idle for one minute.
* Accelerate at normal throttle position (20-50%) until vehicle
shifts into top gear.
* Cruise at light to medium throttle.
* Decelerate to a stop, allowing vehicle to downshift, and use
brakes normally.
* Process may be repeated as necessary.
Manual Transmission
* Place transmission in Neutral position.
* Ensure emergency brake has been set and all accessories
are turned off.
* Start engine and bring to normal operating temperature.
* Allow vehicle to idle in Neutral for one minute.
* Initial relearn is complete: process will be completed during
normal driving.
Some manufacturers identify a specific relearn procedure
which will help establish suitable driveability during relearn stage.
These procedures are especially important if vehicle is equipped with
and electronically controlled automatic transmission or transaxle.
Always complete procedure before returning vehicle to customer.

 

[cruiser54]

That ain't Renix.............

 

[Ecomike]

Read page 88 of the Renix MPFI manual, second column, third paragraph, it explains the min/cur/max data display as an xx xx xx format, first xx is min, second is current, and third is max, and how to navigate....it mentions the down and up keys to jump form sensor to sensor.

 

[Ecomike]

Read page 88 of the Renix MPFI manual, second column, third paragraph, it explains the min/cur/max data display as an xx xx xx format, first xx is min, second is current, and third is max, and how to navigate....it mentions the down and up keys to jump form sensor to sensor.

 

[Ecomike]

That ain't Renix.............

It says 1988, Jeep Cherokee ALL MODELS.

 

[cruiser54]

Something is screwy here then. The relearn procedure didn't come out until the A604 trans and Chrysler had designed the electronics. That procedure is very similar to the one we used for the new Chrysler products during the Pre Delivery Inspection, or for the customer complaints the bulletin describes.

 

[cruiser54]

As far as the DRB, I am familiar with navigating through the sensors. That's what I did this afternoon.
There's a good possibility that DRB changed through the years and don't write off the possibility that a bulletein came out saying the aforementioned bulletin or FSM info was wrong.

 

[Ecomike]

Something is screwy here then. The relearn procedure didn't come out until the A604 trans and Chrysler had designed the electronics. That procedure is very similar to the one we used for the new Chrysler products during the Pre Delivery Inspection, or for the customer complaints the bulletin describes.

It is generally accepted that the Toyota AW4, Renix era TCU does have relearn process, and it also has a full time 24/7/365 power to the TCU directly from the battery. But few have the tools to read it.

I guess we may never know for sure, but I find it hard to believe anyone would build a controller that did not record, save and check the min and max history of various sensors, and use that data in the algorithms for calculating output control settings, and for diagnostics work. What I do know is that I have seen evidence that cycling the switch with out even starting the jeep, and or disconnecting the battery briefly, has on occasion solved idle problems on both my renix XJs after replacing a TPS, or after confusing the ECU with a 15 min on, no start attempt state.

 

[90xj06]

at the time the ecu was designed memory and features where still very limited.
its was basically an electronic carburetor. its looks at inputs and has a predefined output.
how ever occasionally a fault will happen with electronics slightly higher voltage or a quick disconnect and will change a stored value in its state. in which case allowing the circuit to fully discharge will fix.

 

[Ecomike]

We had our first Apple II PC in 1981, and I was writing PLC code for PLCs in 1989 IIRC, that had a fair amount memory for virtual timers, and counters etc.

 

[cruiser54]

We had our first Apple II PC in 1981, and I was writing PLC code for PLCs in 1989 IIRC, that had a fair amount memory for virtual timers, and counters etc.

Yeah, but you weren't working in France for Renault at the time............

 

[lawsoncl]

It is generally accepted that the Toyota AW4, Renix era TCU does have relearn process, and it also has a full time 24/7/365 power to the TCU directly from the battery. But few have the tools to read it.

I'm not sure what the TCU would learn in the first place? Fast forwarding to OBDII, I thought that the P0700 code meant the TCU has a stored code or wasn't talking, and the P0705 (NSS as an example) actually got read from the TCU when queried. I guess the easy test would be to unplug the TCU and see if an existing NSS code gets reported.

That bulletin you quoted sounds suspiciously like something from a Haynes manual - overly general and wrong.

 

[Ecomike]

I was having low rpm upshift problems with my 87 and MPG problems, and while debugging it, I discovered the second red 12V power wire to the TCU on mine was dead. Somewhere along the line I ran a new 12 V patch to it, via a new dash toggle switch. I experimented with it on and off over several months, and while I did not notice any major difference in shifting, I did get a little better mileage on average (maybe 1 mpg) with that hot wire fixed and hot all the time. It was a second 12 V hot all the time wire, not the fused 12 V wire IIRC that must be hot for the TCU to work and control the shifting in D, but a second hot wire, 24/7/365. I really have not given the TCU program much thought before.