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1989 sidekick misfire when cold or when under electrical load
03-19-2018, 11:56 PM
Post: #11
RE: 1989 sidekick misfire when cold or when under electrical load
idle up pin misfire hot and cold, but not with right foot! (odd no?)
no rpm's stated? begin, transition , end. my guess , per post 1. (all normal until fan turned on)

i use a scope on spark to see if park fails, at any rpm, using special probe , spark is first. but most folks have no scope,
if that passes it's all fuel related.
so what is the battery voltage before the fan is turned on, then after, 14.7dc steady is common.
what was the rpm before the fan and after. (800 my guess hot but then as it rises misfire happens but then what?)
the idle up , pin is just that. pin A13, (steering overload) and A2, (the idle up block. AC/fan/)
the diodes are shown here, idle up block.

when does engine run good? im trying to see the full picture here.
runs good up hills flogged? hot engine.?
do head lamps dim , running at any time. (voltmeter is way better way to see this)

EFI processes:
when the fan turns on, lots of current flows, same with headlamps, and both be worse cases, turned on same time. (the diode block is ECU early warning)
the load on the Alternator goes higher. and the ECU reacts, fast.
the current from the alternator goes up say 15amps. (over 200 watts more in demand from the engine, about 1/4th horse power, not much , but at at idle the engine does not have much.)
the engine is loaded by that ,same amount and more (inefficiency of ALT)
the ECU sees the rpm start to fall and opens the PWM duty on the ISC and adds only more air, to reach 1000 rpm. from say 800 hot.
the MAP sees this new air flow and adds fuel exactly to the needs of air. making AFR (air fuel ratio) good, so that the fuel burns perfectly. (NEAR)
if the voltage falls, spark can fail, (weak distrib parts or coil)
if the voltage falls , the ECU caps bad the ECU can do any crazy thing, it wants, even REBOOT (jump to zero reset we call that ) (Can repeat like like mad, endless resets)

idle up is a binary input to the idle speed control software (firmWARE) only changes the regulated speed, (just a number "goal") for the loop.,

ok you turn on the fans and what happens, it hesitates and misfires then runs smooth, or goes to 1000 RPM AND the misfires, or both,
if it fails only in the transition point only that can be lean misfire, but does not explain you doing the same with right foot , works ok.
what is battery voltage at the point of failure and before.?

ON any old SIdekick it's best to check caps. for sure if the ECU acts odd, or codes stop mid stride, during, codes 12s, you can leave in the jumper and turn on the fan does code 12's abort.
does 12 flashes stutter? fan on, if yes, Caps bad, or power to ecu is not correct. this test is not definitive.
one can drive to work with code 12 flashing, and see other things happen doing that, and is harmless to do, just the

see the 2 black ones here left side

the stealthy ones only dry out, and are useless like that.(no splits/bulges/leaks seens/or worse)

The caps, can be bad , for sure the one in the corner, or both adjacent to the connectors.

now the cold deal,
"It will happen regardless of whether the engine is cold or hot." I think you meant it does it only idling and never misfires driving, "
infact this happens when the brand new car, is accelerating, only , and rich happens on purpose.
cold the IAC it wide open, that device, buried in the body of the TB BASE (thermal valve).
when the IAC is open the idle controls (ISC) are dead, only the IAC sets idle cold
so if the IAC is bad RPMs are wrong,
what is RPM after the dash pot releases, ? cold? you said 1500, and is ok.
post 1 says
Car runs pretty good, but it misses when it is cold.
Rises to 2000 rpm then drops to 1500 and slowly to 800. (this is normal, IAC actions, 2000 is dashpot action) 800 is ISC rules. hot , no idle up in effect)
The missing stops when fully warmed. (partially true and corrected below)
It will miss again if I turn on lights or any other electrical circuit that makes Ecm think motor is under load.
Mpg is around 20 which makes me think it is running rich. (this is correct it is running rich, and will misfire rich, after 20mpg is like same as huge V8 engine)
how could a tiny 1.6L get 20mpg,
sure unplugging the diode block , this prevents idle up mode. and will hold rpm at 800 solid, if the RPM drops fast below 800 that means ISC loop has lost control, (or spark or fueling issues)

this old car has no real scan tools (sold OTC). so all work is done the hard way. scopes and meter, ways.
the 20mpg happens these reasons. (and is your best symptom btw)
(Limphome or Lost)
in limphome, , you bet non code 12s flashing, did you drive car with 12s flashing at the same time? ,
fuel pressure is ok, so not that.
ECU is lost the ECU gets lost for many reasons

the word lost means the loop servos can not do there job, (fuel rates top that list)
there are 2 main loops, fuel rates, and idle loops. there are no spark loop here, nor tables in the 89, at all (distrib does this by lonesome) until 1991.
Lost control of fuel rates:
causes of that,?, (fuel pressure ok and is always #1 for 2 reasons, ECU can not change it, nor can it measure it )
injector leaks, no it does not. by testing for leak down test (passes) and looking at INJECTOR eye balled, keyed on say 10 times, not running,
ECU bad, or just caps. sure. (super common fail in all these cars from 89-95)
02 reads too, lean hot. ? (you can unplug it and test for misfire to end) unplugged it goes to 1/2 range (good),lying to the ECU, so it may act better.

02 works only hot so, does not explain cold misfire, but this old ecu are know to let the 02 have to much Authority on Fuel, corrected in 1996, USA. OBD2 cured that.

The ECU sets fuel rates with the Map, and IAT, and ECT
if any of these read wrong, fuel rates can go very high, for sure the map then the ECT.
the ECT measures water temp, and must read per my ECT tables.

lets say the water temp was 40f parked over night. you open hood and pull connector (release its locks first) and then using OHMS on the DMM it reads about 5000 ohms.
if it read 10,000 ohms the engine would want to flood, and for sure misfire.
then i get engine hot, and that is 180f, and reads 300 0hms. if these 2 test pass, then its not the ECT.
The IAT works the same, but way less influance on fuel.
but measure only air temps. hot engine say 100F? or more, avg. but is totally related to outdoor temps, and how much the manifold warms that air as it flows in.
cold air gets more fuel. (dense air is cold and can make more power)
Then the MAP.

IF THE ECU is bad, anything is possible.

the cause is related to rich, way too rich, and spark has hard time burning it , due to the gross rich conditions.
fuel pressure wrong
ECT wrong,
IAT wrong inputs but will not cause above. only make it worse if its wrong and 1 more wrong.
Injector leaks, seems not.
spark bad. (always suspect) or cant handle too rich.
Bad ECU. if all inputs are good and ECU over injects fuel, it is bad.
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Yesterday, 12:02 AM
Post: #12
RE: 1989 sidekick misfire when cold or when under electrical load
I bet the injection rates are wrong.
we scope injectors to see if they are in fact rich, we know the displacement and its TBI and 1 injector.
if its way TOO rich at the injector lines (pins) (pulses way too long)
then we check ecu inputs, for wrong,
if all is good for inputs, the ECU is bad. if map/ECT and IAT read wrong we correct that next. (or 02 wrong only hot)
if the injector pulses are good, the injector leaks or the fuel pressure is out of spec.
if rates are ok
then spark is bad. or engine, has pure mechanical issues.
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Yesterday, 12:10 AM
Post: #13
RE: 1989 sidekick misfire when cold or when under electrical load
I read your post again #1
no new spark wires (mag is best)
new cap.
new rotor
new standard spark plugs? set to .028 " never out of box with gross wrong .045" and no bad to the bone surface fire spark plugs of any shape kind or form , $1.59 spark plugs as car had new.
VR gap set.
checked that both the vacuum advance works, with the a real spark timing light,? and a leak down test on it first? can be seen to work with vacuum connected then not.
then makes sure the advancing weights inside this old DISTRIB still works after 29 years of rusting ? the tests are in the manual. for 89s. it works just alike a 1096 USA V8 engine, this distrib.
discounting the VR and ignitor, the vacuum and centrifugal system is all pure mechanics.
im sure you did that but just want to be clear.
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Today, 06:08 AM (This post was last modified: Today 06:53 AM by Jamestb.)
Post: #14
RE: 1989 sidekick misfire when cold or when under electrical load
Update: First let me say thank you for all your help.

I do have new ngk wires and plugs with Bosch cap. I tested voltage at battery and got 12.3 with car off and 14.6 with car running. I turned on fan and lights and dropped to 14.3. I checked spark with an extra plug and it looks strong.

I tested map and got 1.2 at idle and it jumped to 3.2 on increased throttle. However if I held wot, then it dropped back to 1.2. Is that normal?

Iac and ect are both new and resistance is testing good.

Misfire only happens when idling cold 1500 rpm down to 800. Once it reaches 800 the misfire stops. I can make the misfire return if I turn on lights/fan which increase idle to 950.

Car runs good down the road under all conditions, freeway, city, off road, up hills etc. Of course my mpg is still low 20mpg. Sometimes 17-18.

I am close to just living with it the way it is. I may test fuel pressure again and have the injector cleaned. I'll also check to see if there is a service center with a scope to test injection rates.
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Today, 06:16 AM
Post: #15
RE: 1989 sidekick misfire when cold or when under electrical load
Forgot to mention that I changed the two larger caps in the ECU and have been driving with the diagnostic fuse in and always get a strong steady code 12.
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Today, 08:19 AM (This post was last modified: Today 08:24 AM by fixkick.)
Post: #16
RE: 1989 sidekick misfire when cold or when under electrical load
good symptoms to stump anyone, wow.
try voodoo yet?, just kidding....

id say its way to rich cold, only, cold , too rich misfire. and hot too,but is not Witnessed hot, because only MPG is hurt not driving.
the ECT reads right so the richness (normal is rich cold) but your extra rich stacks on the normal rich A+B=C and misfires.

either the injector IS over injecting by self, or from (fuel pressure must be, 34.1 to 39.8 PSI , & only changes with altitude or is bad, or air filter packed badly or FPR bad to the bone. (some do that with cracked diaphragms... and act odd has hell. (works fails works fails repeats... making catching it hard.)

if the pressure is ok, unchanging, ever. say parked and gunned throttle.
one of the sensors is bad
have you driven with o2 unplugged, in the off chance it's stuck at 0v, (even new one can stick with sneaky hidden exhaust cracks, sucking air)

solid 12s, no skips like tossing an egg at drummer boy, and he gets lost... ecu crashing does same. some cant even do the 12s. (get nothing)

if the O2 test passes, and the pressure is like a rock , unchanging, on flat ground, it must be the ecu. bad or FPR that is grossly intermittent.
the new cars 96+ we can drive all day and log all sensors, and not have to guess, on this car, not easy, (but ive done it the hard way (long wires and meters)

the 20mpg is all we really need, it's rich as miss PIGGY. she is stealing money out or your wallet.
your idle vacuum is great. btw.
cheers and good luck to you .!

PS; if I mention a part on car that is new, it is only to be complete. (or even new parts can be bad, rare sure)

your map is working right and the alternator.
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