1990 YJ is a pain to start in the morning

1990Jrenteia

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Jan 31, 2021
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Costa Mesa CA
I recently bought a 1990 YJ with the 4.2 6. It runs like a champ when it warms up, rebuilt trans, 4-inch lift on 35s (did not regear though) it's amazing. It's a PAIN to cold start!!! it also shakes a lot BUT It takes me about 10 times to start, granted I have never driven a carbureted car but I don't think it should take that long. I pump the gas 3 to 4 times I try to crank for maybe 3 seconds but nothing. After a couple of times, it starts but it stalls out, it never gets to reach its high idle. I've been having to help it stay on for maybe a minute or 2 then it'll stay on by itself. Am I just bad at cold starts (am I doing something wrong??) or do I have an actual problem? I would appreciate the help thanks!! (I have attached some videos hopefully, they help)



 
Sounds like the choke isn't working. I'd start with that, remove the breather cover from the carb do a cold start and as its chuging like in your vid, look and see if the choke is closed or not.
 
Sounds like the choke isn't working. I'd start with that, remove the breather cover from the carb do a cold start and as its chuging like in your vid, look and see if the choke is closed or not.
 
Sounds like the choke isn't working. I'd start with that, remove the breather cover from the carb do a cold start and as its chuging like in your vid, look and see if the choke is closed or not.
What should I be looking for? Should the choke be open? Can it be adjusted or do I need to buy a whole new carb? Thank you so much!
 
Last edited:
To be honest, my experience with my 1990 4.2 BBD carburetor system drove me to convert it to fuel injection. The vacuum system is extremely complex, and over the years, many of the components (check valves, vacuum motors, sensors) are no longer available new.

A couple of thoughts:

The choke circuit utilizes both vacuum and electric control. During start, with the throttle valve closed, vacuum above the throttle valve causes a richer-than-normal flow from the main-metering and idle fuel circuits, enrichening the fuel-air mixture. The choke shaft is connected to a bi-metallic coil mounted on the side of the carburetor inside a little black circular plastic cover. To gain access to that mechanism, you must drill or grind the rivets holding the cover on. This is not designed for easy access, but I did remove this cover which then allows some rotation adjustment capability. You have to come up with your own screws to put it back together. In fact, I believe you must remove the carburetor to work in this area. I had my carburetor off MANY times and replaced it once.

The choke cover has an electric heater that warms the bi-metallic coil and opens the choke. This heater is powered through an oil pressure switch... when the oil pressure is below 4 psi, no power is supplied. When oil pressure is above 4 psi, the coil is powered.

A higher RPM idle speed is built in to theoretically prevent stalling during warm up. There is a fast-idle cam controlled by the choke shaft that rotates against a fast-idle adjustment screw. The cam is stepped to provide a correct idle speed proportional to the choke valve opening. When the choke valve is fully open, the cam rotates free and the engine goes to it's normal idle speed. This cam is accessible with the air cleaner removed.

If you crank the engine with full throttle (pedal to the floor), a "tang" on the throttle lever causes the choke to open. This open position is not wide open, but a built-in open distance normal for operation. This allows starting with no choke, or clearing a flooded condition.

Now, it gets complicated. Idle speed control varies with intake manifold heater on or off, air conditioner and/or rear window defogger in use and air cleaner temp. These parameters are used by the Sole-Vac throttle positioner which is operated two ways.. an electric holding solenoid or vacuum actuator. It goes downhill from there. Just too complicated.

Also be aware of the two tapered metering pins which I recall are visible when looking down the throat of the carburetor with a flashlight. You can see them move with throttle changes. These are computer controlled so as to regulate the proper fuel/air ratio. They are driven by an externally mounted stepper motor.

Another "bad running or starting" issue I encountered was caused by the EGR system, which gets into air cleaner and coolant temps. Again, much dependence on vacuum, not to mention an EGR valve that operates in a very dirty environment.

It sounds to me that you are not getting the proper fuel/air mixture when the engine is cold and are likely struggling to keep it running utilizing the carburetor acceleration pump until it warms up. Possibly an issue with the fast idle cam I mentioned earlier. It may not be stepping as intended. Regardless, you can look forward to some invigorating trouble-shooting, possibly a carburetor replacement, and a journey through Vacuum Line Jungle.

By the way, my only regret in converting to fuel injection is that I didn't do it earlier. That conversion kit is no longer available, but I would encourage you to look at installing a 1994-ish vintage 4.0 and it's associated computer system. If not, I believe you will be forever chasing operability problems. In fact, I don't know how your Jeep got through California emissions testing until now. Somebody must have been keeping things up. I have to wonder that since you bought your Jeep recently, did the previous owner say anything about the Smog testing history?
 
To be honest, my experience with my 1990 4.2 BBD carburetor system drove me to convert it to fuel injection. The vacuum system is extremely complex, and over the years, many of the components (check valves, vacuum motors, sensors) are no longer available new.

A couple of thoughts:

The choke circuit utilizes both vacuum and electric control. During start, with the throttle valve closed, vacuum above the throttle valve causes a richer-than-normal flow from the main-metering and idle fuel circuits, enrichening the fuel-air mixture. The choke shaft is connected to a bi-metallic coil mounted on the side of the carburetor inside a little black circular plastic cover. To gain access to that mechanism, you must drill or grind the rivets holding the cover on. This is not designed for easy access, but I did remove this cover which then allows some rotation adjustment capability. You have to come up with your own screws to put it back together. In fact, I believe you must remove the carburetor to work in this area. I had my carburetor off MANY times and replaced it once.

The choke cover has an electric heater that warms the bi-metallic coil and opens the choke. This heater is powered through an oil pressure switch... when the oil pressure is below 4 psi, no power is supplied. When oil pressure is above 4 psi, the coil is powered.

A higher RPM idle speed is built in to theoretically prevent stalling during warm up. There is a fast-idle cam controlled by the choke shaft that rotates against a fast-idle adjustment screw. The cam is stepped to provide a correct idle speed proportional to the choke valve opening. When the choke valve is fully open, the cam rotates free and the engine goes to it's normal idle speed. This cam is accessible with the air cleaner removed.

If you crank the engine with full throttle (pedal to the floor), a "tang" on the throttle lever causes the choke to open. This open position is not wide open, but a built-in open distance normal for operation. This allows starting with no choke, or clearing a flooded condition.

Now, it gets complicated. Idle speed control varies with intake manifold heater on or off, air conditioner and/or rear window defogger in use and air cleaner temp. These parameters are used by the Sole-Vac throttle positioner which is operated two ways.. an electric holding solenoid or vacuum actuator. It goes downhill from there. Just too complicated.

Also be aware of the two tapered metering pins which I recall are visible when looking down the throat of the carburetor with a flashlight. You can see them move with throttle changes. These are computer controlled so as to regulate the proper fuel/air ratio. They are driven by an externally mounted stepper motor.

Another "bad running or starting" issue I encountered was caused by the EGR system, which gets into air cleaner and coolant temps. Again, much dependence on vacuum, not to mention an EGR valve that operates in a very dirty environment.

It sounds to me that you are not getting the proper fuel/air mixture when the engine is cold and are likely struggling to keep it running utilizing the carburetor acceleration pump until it warms up. Possibly an issue with the fast idle cam I mentioned earlier. It may not be stepping as intended. Regardless, you can look forward to some invigorating trouble-shooting, possibly a carburetor replacement, and a journey through Vacuum Line Jungle.

By the way, my only regret in converting to fuel injection is that I didn't do it earlier. That conversion kit is no longer available, but I would encourage you to look at installing a 1994-ish vintage 4.0 and it's associated computer system. If not, I believe you will be forever chasing operability problems. In fact, I don't know how your Jeep got through California emissions testing until now. Somebody must have been keeping things up. I have to wonder that since you bought your Jeep recently, did the previous owner say anything about the Smog testing history?

So I bought the Jeep from my brother-in-law and he isn't really the mechanic type in fact he doesn't really know anything about cars or jeeps, to say the least. All I know is that he paid to get the trans rebuild and the engine to pass smog. All he could say is that it was a pain in the butt for the mechanic to figure out... or he just paid a little extra to pass it, I don't know it was either-or. I would like to take it to a mechanic but I just don't trust some random mechanic to work on a 29 some year old jeep, there's also no fun in taking it to a mechanic, but if it comes down to take it to one I don't mind I would just want to look for the right one to do the job. I plan on offroading it and taking it on trips here and there so I'm just trying to get to know the Jeep and trying to build it up to be the best it can be to be reliable on the trails. that being said I am considering fuel injection, I just don't really know what I'm looking for. I have seen a lot about the Howell fuel injection kit.

( https://howellefi.com/product/tbi-kit-1987-91-yj-wrangler-4-2l-emissions-legal/ )

Is this something I should go after or are there better / more affordable kits out on the market?? I would like to hear some input about it, if its the right decision to make before spending $1500 or so. I'm all ears.

Thanks for all the information Gary I appreciate it!
 
I looked at the link you sent and it made me feel good about the world again. President Trump was just acquitted AND there are Electronic Fuel Injection kits still available for the Jeep YJ 4.2!

The kit you are looking at is a Throttle Body Injection (TBI) vs my Multi-Port conversion. There are advantages to each, but in a nutshell... I'd give your TBI system a go. One can argue about efficiencies, horsepower and the like, but for the Jeep, I think these differences are small. Your TBI looks to be amazingly simple. I had to change intake manifolds and it appears you keep the one you have. I love the use of an existing 4.3L Chevy Throttle body. I think the cost is very reasonable. AND, I can guarantee you will save hours and dollars on reduced maintenance. Smog tests should be a breeze. I can't recommend hard enough that you switch from the carbureted 4.2 to a Fuel Injection system, including the TBI system you pointed out.

Look, if you are bound to be a YJ owner, as time goes by, you will become a YJ lover. Every investment you make in your Jeep will be appreciated over the years. My Jeep has just over 400,000 miles on it and every switch, button, light, dial and lever works as intended by the designers. In the summertime, I have people parked next to me suddenly start talking about a Jeep they once drove or asking if it's for sale. I've had handwritten notes left under the windshield wipers... "If you want to sell this Jeep, I'm interested. Call XXX-XXX-XXXX". My niece wants me to give her the Jeep when she turns 16, but I intend to be buried in it. Right now, I'm shooting for 1 Million Miles on the odometer.

If you enjoy working on it, there are plenty of mods to consider. If it needs new seats, don't bother to recover or install baggy seat covers... buy new seats. They bolt right in, easy peasy. I never liked the weight of the spare being carried on the sheet metal tailgate door, so I changed the rear bumper such that the tire weight is carried by the frame. Carpeting, LED instrument lights, sound bars, stereo's, whatever... it's all in a weekends time investment. Something quits working, fix it right away. I wouldn't hesitate to hop in the Jeep this afternoon and impulse drive to Texas, or even Disney World in Orlando.

It is always cheaper to maintain the heck out of a vehicle than it is to buy new. The longer you keep it, the more others envy you. There are more sinister aspects to YJ ownership... they become more desirable and thus are targeted for theft. Install a hidden engine kill switch or disabler somewhere. Here in Southern CA, there have been a rash of Jeep thefts from peoples driveways at night. I cleaned out the garage enough to keep this 31 year old Jeep inside. My wife's Mariner sits outside.

Do your fuel injection mod! You won't regret it. If this Jeep was meant for you, it won't be long before you find yourself some Sunday morning sitting on the ground along side the Jeep polishing the exposed frame with WD-40.
 
I looked at the link you sent and it made me feel good about the world again. President Trump was just acquitted AND there are Electronic Fuel Injection kits still available for the Jeep YJ 4.2!

The kit you are looking at is a Throttle Body Injection (TBI) vs my Multi-Port conversion. There are advantages to each, but in a nutshell... I'd give your TBI system a go. One can argue about efficiencies, horsepower and the like, but for the Jeep, I think these differences are small. Your TBI looks to be amazingly simple. I had to change intake manifolds and it appears you keep the one you have. I love the use of an existing 4.3L Chevy Throttle body. I think the cost is very reasonable. AND, I can guarantee you will save hours and dollars on reduced maintenance. Smog tests should be a breeze. I can't recommend hard enough that you switch from the carbureted 4.2 to a Fuel Injection system, including the TBI system you pointed out.

Look, if you are bound to be a YJ owner, as time goes by, you will become a YJ lover. Every investment you make in your Jeep will be appreciated over the years. My Jeep has just over 400,000 miles on it and every switch, button, light, dial and lever works as intended by the designers. In the summertime, I have people parked next to me suddenly start talking about a Jeep they once drove or asking if it's for sale. I've had handwritten notes left under the windshield wipers... "If you want to sell this Jeep, I'm interested. Call XXX-XXX-XXXX". My niece wants me to give her the Jeep when she turns 16, but I intend to be buried in it. Right now, I'm shooting for 1 Million Miles on the odometer.

If you enjoy working on it, there are plenty of mods to consider. If it needs new seats, don't bother to recover or install baggy seat covers... buy new seats. They bolt right in, easy peasy. I never liked the weight of the spare being carried on the sheet metal tailgate door, so I changed the rear bumper such that the tire weight is carried by the frame. Carpeting, LED instrument lights, sound bars, stereo's, whatever... it's all in a weekends time investment. Something quits working, fix it right away. I wouldn't hesitate to hop in the Jeep this afternoon and impulse drive to Texas, or even Disney World in Orlando.

It is always cheaper to maintain the heck out of a vehicle than it is to buy new. The longer you keep it, the more others envy you. There are more sinister aspects to YJ ownership... they become more desirable and thus are targeted for theft. Install a hidden engine kill switch or disabler somewhere. Here in Southern CA, there have been a rash of Jeep thefts from peoples driveways at night. I cleaned out the garage enough to keep this 31 year old Jeep inside. My wife's Mariner sits outside.

Do your fuel injection mod! You won't regret it. If this Jeep was meant for you, it won't be long before you find yourself some Sunday morning sitting on the ground along side the Jeep polishing the exposed frame with WD-40.
It really is a good time in the world ain't it haha. Man, I can't thank you enough. I'm gonna give that TBI system a go. If this is the Jeep community people are always raving about then I'm all in, not only were you helpful but I appreciate the stories and the incite. I'm only 20 years old and I hope my Jeep can last as long as yours or even past my lifetime. The Jeep only has 190k miles so I have some catching up to do haha. Again many thanks!!
 
all I have are questions... blind.
first off atthe get go. how may months? was it parked not driven.??? was the fuel ever bad? is this car a DD? please say so or what.
most carbs made, you press the throttle pedal 1 time and this is called the fast idle cam and choke unloader event
air cleaner off, hood up move the cold engine throttle by hand see if the choke BBD ,unloads from open to closed. mostly closed.
the fast idle cam must work also for more fresh air.
Most cars I owned (vast) with carbs, is converted to a manual choke , ending all this silly auto choke trash.

my guess #2 is the float bowl is now dry or way way too low, and or the float needle is all gummed up as all carbs made for 100 years loved to do all the time or at the drop of a hat. old fuel causes it. called GUMMED up.
or the fuel pump is failing.

I you buy a can if instant start spary , it will not start?,so again air cleaner off, see choke plate , lift it open spray for 3 seconds

if it does not run now SPARK is bad. ever do a full 60k mile tune up?, with cap/rotor/hv spark wires and spark plugs gaped
to the numbers stated under hood look up and under the EPA sticker is there to read. (USA cars)
the chokes are tuned for you climate and altitude both. or it fails.

yes the jeeps are stolen. after all it is child's pay to do it.
the best cure is a hidden switch you put in.
nothing works better and the more well hidden wins all bets.

one good upgrade to carb cars is a electric fuel pump 7psi not EFI 70psi
and the hidden switch , runs this pump.
now if the new pump can not be hot wired there is no stealing it.
NEcro post #2 , for those with BBD horror. (

the electric pump fills the float bowl fastest, in say seconds key on, then crank, a huge win. done many in 50+ years.

cranking and engine over and getting the cam pump to fill the bowl full is painful. (to the battery mostly)
use test spray fuel
if test fuel fails (at the get go ,not flooding the engine first cranking it)
also the chock set too rich makes it flood the engine, and we all now LA weather , the choke must be set leaner. per the FSM
the coke stove has scale lean normal rich and the book IIRC it says start 1 notch rich. on the dial, and tune it so it starts faster
at your normal air temps and less at high altitude.

if really worried hide the pump above the fuel tank hidden. so the thieves can not find it.
on 92 up the pump is in the tank. (EFI models)

stolen cars are sent to mexico, oldest story ever, I lived there in 1970 part of Vietnam tour.
my best friends brand new Harley, (he saved money , in Nam for 2 years to buy it for cash) and day1 San Diego, stolen.
they also stole all my tools then,.

reCAP
stock pump weak
float bowl low
float need gummed up and frees up a tad warmer
choke plate release dead, so sure is on on warm hot starts sure.
spark is bad or weak.
choke. set wrong per climant /altitude

Most of these 30 year old BBD carbs are a miss now. so there is THAT>

a 5 min fix stuck chock
or $1600 TBI kit.
or the spark plugs are bad again. and again.

hummmmmmmmmmmmmmmmmmmmmmmmmmmmm
when starting a post and say this.( Okay?)
1: I want folks to only gue$$.
2: I want to learn how to test and diagnose the problem ,even buying tools not in the shop now.
or if reading the FSM is out of the question. DO read it first. and when confused say here you get confused. (99% do)
3: or ? be clear on that, and posts can be short or long, I guess bad chock, .

the first 2 tests are, is the choke unloader working and if does at first press of throttle does that and the coke plate go closed 90%
the FSM shows how to set all that, BBD pages.
lucky you it runs hot.
or convert it to manual choke.
yes it can be adjusted, the FSM is free

I will paste that here to you in the carb fuel chapters,
90 yJ 4.2L
BBD carb.
just saying.... if you have a 34 old jeep, get the FSM first. and learn to fix it your self
most shops the techs there never seen or touched a car this old. for sure MCU BBD carb wonder device there.
the choke unloader mech. releases the choke (from hot mode) to cold. and also raises the thorttle plate for fast idle. cold start
the fast idle is also called a fast idle cam. and it too has spec. adjustment.
chapter 14, page 122 is where it starts for 4.2l liter engines, the book cover all fueling of all enfine that year. YJ and more

the main jets are stepper motor , MCU ( computer controlled and uses 1 OX sensor to do that in closed loop mode.
The chock is old skool (sic)
and 1, KS knock sensor tool and lots of thermal switches , WOT and more.
step1 , make sure the altitude jumper is not in place (jump it over 4000ft, altitude) what the PO did here is any wonder, so look.
step2. the SOL vac , must work and idles switch and relay so the idle controller can work hot and cold both. page 126
the system is very complex , compare to a simple real carb. yours is e_carb. (horror)
step 3 is the choke relay told page 128 and needs a working oil pressure switch to do that , as it states. see the 2 fuses p130?
the pages go to p156, with complex carb related diagnostics.
this ends CEC end of this carb
page 104 is BBD basics, to p121 Chapter 14, only
page 105 cover the chock adjustment/

the choke is electrically heated, if this burns out (gee 30 years old) the choke is dead.
read page 107, it tells you the carb must be removed to fix or set the choke up. (but the oil pressure switch must work)
the choke is color coded, it says and we set that based on 3 factors climate , altitude and if a relic choke there we may need to go richer for it to work, if it works at all , sure.)
page 118 unloader adj.
and last 119, choke actuall colored settings for gold ,red, or green model index.
the fast idle cam must be set too, per the book. in order .

free to read here (huge chapter 14 and 104 on)
PDF ICON first one, is BINGO

most guys just go old skool normal carbs and a HEI , spark coil, needs to computers at all spark. ( A MOD common)
if lucky only one part is bad and not the carb.
the book tells you how the coke is unloaded running cold idle if the driver, pushes hard the throttle pedal if this vacuum parts fail
called vacuum unloader goes dead the engine floods
if the chock plate is dead (means stuck fully open in a virtical position, then it is 1 of 2 things caused.
the coke is dead. (bi-metal spring heater inside DOA) or the choke rod is simply jammed. (we must depress the throttle before cranking any carb car to release the choke. if not it is jammed or is a dead choke heater.(guts in side it)_

all carbs are in fact tuned for climate. (key west and alaska are not the same) and denver we must run the choke learn. or it floods
History and other cures. for CEC computerized engine controls, BBD horrors.
this jeep should have (day1new) been TBI , injected. doing this CEC BBD carb deal is a horror, If I had it , it be GONE.
there is nothing wrong with TBI, EPA banned all of them in 1995 . as was CEC long ago.
but only for cold starts. fuel pools up in the below TB , plenum and the cold cat, lets HC smog happen. raw fuel out the tail pipe.
so they banned it. Calif banned it first. other than that, we love TBI. just 1 injector to clog, o_O
MPI is the cure then and now. (or GDI)
A real old BBD carb (non CEC) is way better and HEI dizzy mod.
the oldest BBD can work ,it did on old CJ's (nothing wrong with simple carbs , for utility, or for prepper cars.)
leaving only spark to worry . (the nutter mod too is common )


Custom TBI is like $1600 kit, a crazy price just for that.
but if the chock is only bad, we can buy one.
SMP (TOP MAKER) MAKES IT


AS SEEN HERE AND NEEDED
how far it closed depends on how cold it is and if too old and now weak. or how it was adjusted, as seen say in Hot florida
Come on man, the thread is over three years old and the guy who started it hasn't been here since September 2021. Do we really need 5 of these posts in a row?
 
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Dude, a lot of times you post good info, but every time you post it's buried in multiple walls of text posts. Just a few minutes ago you posted to a thread with a gigantic post that had nothing to do with the OP's bent pushrod after the OP had already posted that he had figured out the problem and what it was a half hour prior. You've been on the forum for 154 days and have posted 420 posts and almost all of them are very similar. Huge walls of text.

Like I said, you bring good info to the table a lot of times, but whoever is reading it has to find it in your pages long posts.
 
im not a dude,
ill just not post at all,
and my other post was before his. ok, he posted as i typed, that is a fact.
so lacking walls of text, only guessing is possible.
i guess social networks are for low attention span readers and is free advice
I have no reasons to be here only to help, so Im gone, have fun guessing
If you do not like long lists of help to find 50+ causes, learn not read them.
really learn to read what you like, is that hard to do?
gone
gone, I don't need you so...

:ROFLMAO: