Cold start problem on 92 2.5

JohnOllen

JohnOllen

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Joined
Dec 4, 2023
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11
Location
Ontario, Canada
I‘ved searched on this “common problem” but haven’t found anything yet to lead me to the solution. Most solutions seem to point to a tired ECM. My YJ runs great, starts great when’s its warm outside, but once the temps start to drop to near freezing it takes its time, several cranks before it fires to life. Once it starts it runs great, and starts great again.The weird thing is if I plug the block heater when it sits out in the cold, it‘ll fire right up, even on the coldest morning. The only thing i would think the block heater should help is with keeping the oil warm and thinner, so the starter has less problem turning it over. It does turn over a bit slower in the cold but the battery is fine. Could it be the starter is just too old and tired to turn it over fast enough to fire in the cold? Seems to turn over well enough to me but like I said it is definitely a bit slower in the cold.
Other info:
- CEL lights up when key is turned to on, then turns off when engine starts.
- fuel pumps comes on with key going to on,
- fuel pressure in rail checked and found to be 29psi 24hours after it was shut down.
- Battery fully charged
- spark plugs cleaned
- intake air temperature sensor cleaned and verified working
 
JohnOllen said:
None
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I guess my biggest question is why would a block heater make it start right up in freezing temperatures if the problem was being caused by a tired ECM or a bad sensor or even a weak coil. I can’t think of anything the block heater would help on initial startup other than the starter motor.
 
I would check your wires for loose connections and clean grounds and test starter current draw. Here is a good set if the wires have never been changed (they can corrode internally):

www.jeepcables.com

Jeep Wrangler YJ Big 7 Battery Cable Kit (1986-1995)

This upgraded battery cable kit replaces old worn out battery cables for more power and better performance from your vehicle. What is the "Big 7" Battery Cable Kit Our "Big 7" kits include the standard "Big 3" cables: alternator output to battery positive, battery negative to frame/body and...
www.jeepcables.com www.jeepcables.com
 
I second looking at your wires. On a different vehicle, I had the same symptoms and turned out that I had corrosion throughout the battery cables. I replaced them and it fired right up during the cold months every time.
 
redbullet said:
I would check your wires for loose connections and clean grounds and test starter current draw. Here is a good set if the wires have never been changed (they can corrode internally):

www.jeepcables.com

Jeep Wrangler YJ Big 7 Battery Cable Kit (1986-1995)

This upgraded battery cable kit replaces old worn out battery cables for more power and better performance from your vehicle. What is the "Big 7" Battery Cable Kit Our "Big 7" kits include the standard "Big 3" cables: alternator output to battery positive, battery negative to frame/body and...
www.jeepcables.com www.jeepcables.com
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I like this idea, thank you very much. Extra thanks for including the wire set to order. Will order and install and let everyone know the results. Today it started a little slowly after sitting in a 60 F degree garage over night. Left it outside all day in -2 C temps but with the block heater plugged in, started up instantly tonight. It really likes that block heater. Lol.
 
I'm not sure what's normal for a '92 2.5L on a cold start. Summer or winter my 92, 2.5L sounds like it takes four compressions (1 each of 1-4 cyl) or two seconds of cranking before starting when it's been sitting overnight. Each start thereafter during the day is great and fires up right away. Same as the OP, all pressures are good and all tune-up items are new. I even tried cycling the key on and off to make sure the pump has primed the injectors. (guessing). This first start of the day is always the same.
 
Flyer58 said:
I'm not sure what's normal for a '92 2.5L on a cold start. Summer or winter my 92, 2.5L sounds like it takes four compressions (1 each of 1-4 cyl) or two seconds of cranking before starting when it's been sitting overnight. Each start thereafter during the day is great and fires up right away. Same as the OP, all pressures are good and all tune-up items are new. I even tried cycling the key on and off to make sure the pump has primed the injectors. (guessing). This first start of the day is always the same.
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Have you ever put a fuel pressure gauge on the fuel rail to make sure you aren’t losing fuel pressure in the rail overnight?
 
JohnOllen said:
Have you ever put a fuel pressure gauge on the fuel rail to make sure you aren’t losing fuel pressure in the rail overnight?
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Yes, a year ago it dropped just a few pounds over a 6 hour period. I'll check it again. Pressure with only the pump priming and after start are normal when doing the test in the FSM.
 
Flyer58 said:
Yes, a year ago it dropped just a few pounds over a 6 hour period. I'll check it again. Pressure with only the pump priming and after start are normal when doing the test in the FSM.
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Sounds like that rules out pump, pressure regulator and injectors. I'm going to go ahead and replace all the starter motor wires. Will post the results But I’m not sure how the wires could explain your similar cold start issue given your warmer climate. I’m beginning to wonder if our old engines are just fairly cruded up in the piston rings and such and when the engine and oil doesn’t have some residual heat in it from running, it just cranks slower and hence takes longer to start. It’s just bizarre how fast it starts on all but that first cold start.
 
JohnOllen said:
bad sensor or even a weak coil.
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so no spark tune at 60kmiles? (all words posted is car parked outside , first start cold?)
32F it starts up slow.
so is the starer spinning too slow, is the battery voltage below 11vdc cranking cold? hummmmm
yes the block heater warms up all that, including the 4 injectors and fuel through them and cold fuel does not like to burn. (for sure if tank is full of summer fuel.) (fill up the tank with winter fuel. top off?)<< the makers of fuel adjust it for cold)
The pressure is good so it is not fuel pressure
the block heater also makes cylinder compression higher, and less friction with cranking, too. ( and sure the starter spins faster for sure old tied batteries)
for sure.
check compression?
the IAC likes to gunk up and stick so if stuck closed how can the engine start with no AIR inducted, so clean that first.
To make sure the IAC is not bad learn to crank with 5% throttle foot. just tiny bit. and if it starts fast , it needed AIR,.
Load test the battery yet>? if it is old and weak then it cranks slower cold , as the all do old.
  • good spark
  • good battery (check voltage cranking) if fails cold try jumper cables see if this simple tests proves the case, simple no?
  • good compression. (tested WOT) x4
  • good fuel , not summer grade. (some additives can help) try Techron injectors cleaner in tank. ( i never do snake oil but this is good)
  • try 5w-30 oil?
  • IAC on the TB, must work for sure cranking and idling. (needs air or fails)
  • key on fuel pressure at spec, (and is)
  • the ECT must read 300 ohms hot, does it? and cold it reads at 32f (0C) - 5800 ohms( sensor unplugged)! if reads wrong injection rates WRONG.
  • the IAT reads same as ECT first start if intake man. at 30F overnight they equalize. see?

ect chart I made the hard way from data from SMP sensor maker USA.

oops wrong chart

ect-ohms.JPG
 
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it's not the ECU, that we prove testing, unless rich$$ thick wallet. (99% are good, sent in) so....
if ECU is bad it only needs a RECAP job for $5 , done many.
The inputs to ECU are first, all computer made compute wrong if input are wrong, called "GIGO"
means garbage in , garbage out. (sensors) "gets you"
old fact as the oldest computer on earth.

2nd cause (not engine, fuel, and bad spark/battery) is bad output actuators. (IAC ,injectors. etc)
most old ECU go nuts if battery drops below 10vdc, and is too low cranking. so if spark is dead cranking ?,check voltage first.
when the voltage drops (battery) sure bad lugs. the ECM onboard regulators can not handle the low voltage. and just drop off line.
newer cars can do 9v but have special LDO regulators not invented in 1992.
Jeeps this old need a strong battery, jumper cable it and find out.? what can be more easy? IDK>?
good luck finding it.
 
PCV gasses (fumes nasty) on all these cars put a cloud of blow by gasses in the intake plenum that can land on the IAC valve cone .
this is called GUNK
and if it gets to 32f or colder, the gunk is now glue. (bad news) and super common,.
when you turn the key on, the ECU sees 32f from ECT and IAT. sensors. ( oops summer is gone)
then goes to its magic look up tables (firmware) and computes 2 things, (3 really)
it computes injection rates on predicted fuel volatility, (super important) (1fuel,2AIR,3:RPM) (and retards spark too)
and IAC air needed to best burn that cold and or old wrong season fuel. that is and RPM goal too, at first start.
just like the choke did on the 1987 with carb fueling. and the fast idle cam is the old way that IAC replaced on yours. The 87 choke plate was fuel mix.
It can not burn fuel lacking air.
There is no other air source , feet off the pedals.
end topic why it fails. (IAC)
 
Dorf said:
PCV gasses (fumes nasty) on all these cars put a cloud of blow by gasses in the intake plenum that can land on the IAC valve cone .
this is called GUNK
and if it gets to 32f or colder, the gunk is now glue. (bad news) and super common,.
when you turn the key on, the ECU sees 32f from ECT and IAT. sensors. ( oops summer is gone)
then goes to its magic look up tables (firmware) and computes 2 things, (3 really)
it computes injection rates on predicted fuel volatility, (super important) (1fuel,2AIR,3:RPM) (and retards spark too)
and IAC air needed to best burn that cold and or old wrong season fuel. that is and RPM goal too, at first start.
just like the choke did on the 1987 with carb fueling. and the fast idle cam is the old way that IAC replaced on yours. The 87 choke plate was fuel mix.
It can not burn fuel lacking air.
There is no other air source , feet off the pedals.
end topic why it fails. (IAC)
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Thanks, I haven’t checked my engine coolant temperature sensor yet but will do so now.
 
all, cars up there love block heaters, heck, some job sites have parking with the AC power JACK right there. for the block heater
.not fun at 6pm in the dark and will not crank fast, dead cold....
there are more causes too. (ice ups of many kinds)
some cars the intake allows water vapor to get into the MAP sensor hose and clogs it with ice,make the MAP dead.(until it thaws) some cars even have recalls on this. The the PCV is blow by and blow by has moisture. Burning gasoline makes water too. not just smog, CO,NOX and HC)
make sure the air cleaner is not freezing up.too. or getting wet some how, like we see with non stock air cleaner boxes.
worse is short runs, the engine never fully dries out ,see? even this matters. (icing issues)

when you say it will not start
that can be ?
cranks fast not start ( or said slow to start)
cranks slow and no start. or is slow to start (slow slow) see how the word slow means little. (we cant hear it is why)
a starter motor can do 300 rpm with a good battery.
The block heaters in many places are not options. (a high CCA battery is best too) the more north you go the more CCA you need.
I have friend that lives near the North POLE. (Indian guy) Nunavut, Canada
it gets so cold there in his jeep the 50% antifreeze freezes. yah! so goes higher AF.% and lots more problems.
Up in alaska my Nema friend ,they do not turn engines off at all, on tractors and heavy equipment. On some they spray the whole engine with expanding foam.
There are lots of problems in the cold country. It is a near endless topic, for sure not using block heater when needed.( for lots of reasons not just 1)
Me I like the loop heaters with pump (in line with the heater core hose, those really work great.. AC heater+tiny pump.
 
also if super cold the ECU must use lots of extra fuel. and can even flood the engine easy,
the cure is wot cranking WOT wide open throttle, the ECU cuts fuel fully, and clears the flood.
and if IAC dead, it will want to flood so there is cure 2 for IAC failures. 5% cure, and the 100% wot cure( or how how to hide the failure)
when any car will not start try those. 2 ways,
The fuel when very cold will not vaporize well. (it just makes puddle of fuel in the intake runners.(and beyond)
The block heater works in many ways , all good.
The TBI engine is even worse and is why EPA banned TBI, (1 injector TB) good you have 4, MPI.
 
Checked the ECT and found it reading 14500 ohms at 65F. That is apparently what it should be reading at 0F so I will install a new sensor and so how that works out.
 
Just to be more clear, my Jeep has always started, it is just taking longer to start in the cold weather, on that initial start. It does crank noticeably slower during that first cold temp start, but just slower, not struggling to turn over slow. Block heater cures all But I never used to have to use a block heater much so something has changed.
 
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