• NAXJA is having its 18th annual March Membership Drive!!!
    Everyone who joins or renews during March will be entered into a drawing!
    More Information - Join/Renew
  • Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

possible fuel starvation

HJ88

NAXJA Forum User
Location
Washington
I got all the wiring figured out with the ignition side of things... and everything appears fine.... but now i've noticed something different... i removed the air intake hose from the TB... and while cranking the engine we shot starting fluid into the small port ontop of the TB by the idle stepper motor... and afew quick shots say 1 a second and it kept the engine running... now i'd say this is fuel starvation.... but thats just me.... my jeep hasnt been able to start and idle for months now... it just cranks over and starts then dies straight away... not like immediatly like you just turned the ign. switch off, but kind of a slow death.... only runs for 3/4 - 1 1/2 seconds tops... any ideas....thanks...
 
If you shot starting fluid in it and it ran, then it is definatly a fuel problem. Is the pump running? Check fuel pressure? Is the filter cogged? See if you have fuel at the rail--if not remove the line before the filter and see if fuel sprays out with the key on, if so its a clogged filter, if not its the pump.
 
Possible the balast resistor or the wiring is open in the fuel pump circuit. During start, the current bypasses the resistor, goes straight to the pump, when the key is released, to the run position, power to the pump is routed through the resistor, then to the pump. Could be getting fuel during start but not in run.
Just a possibility.
Resistor is easy to check, with the key in the run position, should be getting 14 volts in and 9-10 volts out, checking with a volt meter, to ground from the spade connectors on the resistor.
The change over for the fuel pump (start and run) is controlled through the starter relay, near the battery. Could be something hooked up wrong there.
 
ive already checked the ballast resistor and it checks out fine... i've even skipped the resistor with a peice of wire and the same thing happens... i'll have to check the started relay.... although i havent done anything to it for along time.... so i doubt its that... altough if a wire has corroded off... i duno... i'll check
 
ive checked the ballast resistor and its fine.... i'll have to check the starter relay, a wire may have corroded off... thanks everyone
 
I had an old R-12 freon gauge around, that works just fine for a fuel pressure gauge, the hose and hook-ups are even compatable with the fuel rail connection. It even has a depressor tit, in the end of the hose for the valve stem, in the fuel rail pressure test point. Freon is also a solvent, gas has never messed with the gauge (or hoses) for the 15 years or so, I´ve been using it.
Haven´t seen it on an XJ, but corroded connectors, has been a problem on a few YJ´s I´ve looked at. Voltage checked through the wire (pricked the wire through the last lead running to the pump), with the pump running and everything connected showed some very low voltages. Rare, but something to check when all else fails. Should be pretty close to the low voltage reading at your resistor.
The last time i pulled my fuel filter nad banged the in end on the grounds a few times, I was a bit shocked at all the crap that came out of there. I installed a filter out of a Honda, that fit in the stock location with a little bending, about twice the size/volume of the stock filter. Finer filter, more volume and half the price (of the dealer).
 
ha, i thought my first response didnt get posted.... ah damn computers... but anyway... i dont think my fuel filter is clogged, because it will start and run for about a second every time it starts.... it just wont continue running..... i got a fuel pressure guage today and am gonna test it tommorow...
 
oh and i thought that for some reason that after it switches over to the run circuit that its shutting off the fuel pump... if so, would it be possible to use a jumper wire on the diagnostics port (D1-5 and D1-6) right after it starts to keep the fuel pump running? obviously this wouldnt work for driving on a daily basis but i thoguht it might work to see if thats the problem..
 
I hope we are talking about the same model XJ (pre 91). The fuel pump circuit is (mostly) an orange wire with a black stripe (88). The fuel pump relay is closed when the ignition is in the run position, then power runs to the resistor, orange wire, 14 volts in, then orange wire, 10 volts out to the pump. The resistor/fuel pump relay, is bypassed, when the stater relay, is energized, (with the ignition in start position), orange w/blk stripe (at the starter relay), wired straight to the pump. Believe it´s even orange with a blk stripe at the fuel pump, though I think it changes colors a couple of times, while traveling through the XJ, but beleive it´s changed back to orange at the pump.
Is it possible the fuel pump relay has corroded contacts? Second from the rear, near the battery. Try changing it out with the A/C relay (front). Fuel circuit shouldn´t be too hard to check with a volt meter or even a trouble light.
I´d recommend you get a FSM for the wiring diagram, but know from experience, it is protrayed poorly in the diagrams. Hope my explanation is clear (as mud :confused1 ).
Probably the easiest way to do a quick check, is to check for power in the back, prick the power lead to the fuel pump (probably orange) and test to ground with the ignition on and in start. Should be about ten volts in the run position and around 9 volts during a start, but the voltage at start can vary with the charge and condition of your battery.
Hope I´ve helped some and not confussed.
 
Last edited:
the relay is fine, but i swapped relays and the same thing happened.... i have the FSM and it does help quite abit looking at the schematics... i bought a fuel pressure test gauge and tried it today.... during startup it reads ~40psi, which is what it should according to the fsm.. and even after it dies theres still 30psi in the fuel rail. and after starting it again and keeping it running for about 7 or 8 seconds on starting fluid, the pressure stays at 30psi...? so WTF is going on... the pressure is sitting there waiting, but the injectors arent firing for some reason, correct? this is all i can think of, i mean the pump must be working properly but even if it isnt there is still pressure there to be used... i'd think that its a pump problem if the pressure slowly dropped down to nothing, but it stays at operating pressure. Is there different circuits running the injectors during the start and run circuits? could a faulty sensor be to blame? thanks so much for all the help :)
 
There is a start and run ignition circuit, have to have a look at the schematic. During start a little more juice is supplied to the coil.
OK, fuel pressure is OK, next step, take a plastic hose or something and listen to an injector while it´s running (or trying to start), you can hear them clack when they are cycling. Should be steady and rythmic, just like the ignition. If not a sensor, or the wiring, is messing with ECU imputs, to fire the injectors.
Plug the vacuum line at the transducer (near the EGR valve). Just for a test. If the EGR is stuck open, the motor can die right out. If the EGR solenoid is unpluged or there is no power, the default is continious vacuum to the EGR, causing it to stay open (motor stalls at low RPM).
I checked some posibilities in the FSM, they say weak CPS and a dirty throttle body and idle air motor can cause stalling at start-up.
Disconnect the flange at the cat and try a test start and make sure your exhaust isn´t plugged, have heard horror stories of guys replacing every semsor on the motor, to find out later, it was a plugged catalytic converter.
Take an old plug, open the gap a bit (.040- .045) and hold it to a good ground (a rubber glove advised) with the number 2 or 3 spark plug cable hooked to it. Should be a nice sharp spark, mostly blue, if it´s a pale yellow, large and splatters, it indicates low ignition voltage.
Check to see if the vacuum plug for the MAP sensor, isn´t plugged upside down into the throttle body or the plastic vacuum line to the sesnor isn´t broken.
 
Last edited:
well, about 3 years ago i removed the cat. so that cant be the problem, but tommorow i'll check the spark to see if its any good... and try plugging up the egr vacuum line.... and test the map and cps sensors according to the fsm... just how much do replacment CPS sensors cost?
 
HJ88 said:
well, about 3 years ago i removed the cat. so that cant be the problem, but tommorow i'll check the spark to see if its any good... and try plugging up the egr vacuum line.... and test the map and cps sensors according to the fsm... just how much do replacment CPS sensors cost?
Eagle did a post about a modification, to bypass some of the connectors and shorten the wire between the CPS and the ECU. Said Chrysler had a kit, that´s not real expensive. If the CPS, pulses good and is within specs. it could be the connector or resistance in the wiring.
If we narrow it down to the injectors not cycling, troubleshooting gets a bit more focused.
The only CPS problem I´ve ever personally had, is the lead to the CPS got cooked on the manifold. Had a problem with the injectors and erratic pulses (sometimes they´d pulse and sometimes not), it was a broken/fatigued wire in the injector rail harness, right where it made the bend near the firewall. Read latter, there was a notice, to check the harness near the firewall, so I guess my problems weren´t unique.
Do you have the C 101 connector in your XJ?
 
dont know what a C101 connector is... but i did check the CPS sensor... 227ohms... so its withing range.... this is getting to be such a pain in the ass... im too damn broke to have someone who really knows whats what with the renix system atleast look at it... and if i did have the $1000 it would probably cost i'd go to the wrecking yard and get a ford 302 or something drop that in there....
 
Hey man, i had the same problem before i had my engine rebuilt, let the builder test and tune the motor after i installed it. He found a corroded ground wire, solved the problem, it did stump him for a few weeks though. Check all the grounds and that big electical connection box above the brake booster. Clean and grease it, it gets corroded and produces the same no start syndrome. Hope this helps. Good luck.

Cory
 
well, i feel like a dumbass.... i was just about to give up on it when i flipped through the renix diagnostic chart again... and i noticed that the relay diagram was different to the one that i had been using.... so i went out to the car and tested afew relays, and swapped the O2 sensor heater relay into the fuel pump relay and hopped in the car, crank it over, boom fires right up... i almost passed out from joy... was idling abit rought but thats probably just do to the tps being all messed up and having no O2 sensor heater or something... i do notice that when i hold the TPS at just the right angle it idles great... i love my exaust i wish i could remember what brand it is... it sounds like a dragster idle... ba-boom,, ba-boom,, ba-boom... i love it, far better than a flowmaster IMO...sounds like a 454 (ok not quite) so afew afew hundered bucks and afew months of fiddling, it turns out to be a $20 relay (smacks head). oh well, atleast i know that all my sensors work:D.. thanks goes out to everyone for their input... too bad im a moron and decide to double check the easiest thing last ;)
 
The O2 heater relay and the fuel pump relay share a curcuit, so don´t leave it unplugged or leave a bad relay in there. I was at the junk yard and found a late model BMW, opened up the power distribution box in the engine compartment and now have relays for the next decade or so (Germans love there relays).
I keep a loose leaf folder for my XJ, with a complete maintenace schedule, invoices and printouts of usefull stuff (call in an annex to the FSM). Also made my own checklist, most always check the same things, swaping the relays around is about number 5 or 6 on the list. After you´ve run down the list a few times, you can do it in an hour (or half an hour in a rush) and most times narrow your problem down to a specific sub system fast. Cuts your troubleshooting chores by about 75%.
If you run in the mud or water much, your probably gonna need to troubleshoot again soon. Can modify your checklist, to cover the higher probabilities first.
relays don´t often go bad, it´s usually green stuff growing on the relay spades or the wiring under the relay block. Might want to pull the clips and turn over the relay block (carefully) and have a look see.
I wouldn´t call it wasted time, all part of the learning curve. After you´ve made the same mistake, more than a few times, we´ll call you a quart low on the dipstick, moron is kind of harsh.
 
8Mud said:
we´ll call you a quart low on the dipstick, moron is kind of harsh.

lmao...

well i got it running and all, and just put the new relay in, and put the O2 heater relay back in its place and it runs much better now... but.... i had to retap the mounting holes for the TPS sensor in the TB... so now i have nice easy to adjust allen head screws in place of the stripped out screws that were holding it on before... and i adjusted it to 4.15v, which brings me to my first question, in the renix manual that i found, it say input voltage should be 5.0v, and output should be 4.15v, then it says something about dividing the output by the input and getting 83%... now my input voltage is 4.65v, and i set the output voltage at closed throttle to 4.15v.... making the ratio ~89%... if i keep their 83% ratio i would have to set the output voltage to
3.86v.... so my question is this: what is more important, the input to output ratio or the final output voltage? my guess is final output voltage but thats just me....

and for my second question... i get it to idle at ~800 +/- 100rpms when its in park, then when i shift into drive it goes down to ~600, which is good... but when i gas it to about 3000 or so rpms then take my foot off, it either goes down to about 100rpm then does back up to about 600rpm, or it just dies... or if i drive it and come to a stop, it will either idle at about 200 +/- 50 rpm or it'll just die... so my question is, WHY THE FK does it do this? is it a dirty TB, bad ISS motor, TPS not adjusted correctly (refer to question 1), or what?

ok question #3... on an unrelated subject, is it possible to swap the fittings ontop of the valve cover? if possible i'd like to move the vacuum hose fitting up the the front so when i get my homemade kn filter in (ordered filter, should be herer next week, damn thing was $80... dont know why it cost so much more than from other places, but i dont really care, atleast it'll last forever) i'd like to buy one of those little filters that just pushes right into the top of the valve cover, and since theres not enough clearance in the front, i thought i could put it in the back. (yeah i know i could cut a hole in my hood and have this little 3" filter stick an inch or so out of my hood, but i think people would openly laugh at me;))
 
The TPS is in two parts, one part is for the tranny TCU and the other part for the engine controller ECU. The imput and output voltages seem to have some influence on how they operate, but the control units TCU and ECU, seem to operate somewhat, on a ratio or the curve of the output voltages. In other words they seem to have a somewhat variable base line.
Having said that, mine seems to operate just fine at about 12-14% (or 86-88%) or around 4 volts (4.63-65 in voltage), depending if your measuring the TCU side (front) of the TPS or the ECU side of the TPS. Just a curiosity in passing, the voltage goes down on the TCU side of the TPS and up on the ECU side of the TPS as the throttle is opened, if I recall correctly. JNeary`s recommended the 12-14% (86-88%) setting, has worked better for me than the 82-83% setting recommended, by the FSM or AllData.
Another piece of usless information, is the TCU supplies voltage to one side of the TPS and the ECU to the other and they rarley match. Guess it´s all a compromise.
I think I have mine set at 4.63 in and 3.9-4.0 out on the TCU side of the TPS. Torque converter lockup seems a touch late, but acceptable.
Seems a lot of the sensors have some imput into idle, O2 sensor, TPS, IAC, MAT sensor, ECU coolant temp. sensor (lower left of the block), the O2 sensor heater circuit, maybe even the knock sensor and the MAP. The over all motor vacuum and vacuum circuits.
TPS sensor, IAC (piston and seat gummed up), vacuum circuits and the O2 sensor (wiring, connectors or dirty probe), seem to be the most common problems. The FSM says, CPS and dirty throttle body. At idle, I´ve noticed a bunch of XJ´s run slow (low idle) and rich. Think it´s often, that the ECU, gets confussed with conflicting imputs and defaults.
Yours kind of sounds like a sticky ISS (IAC,idle air controller), but could be a vacuum problem, O2 circuit or other sensor values. Or a combination of a whole bunch of things.
My idle changes about 200 RPM, pretty much right with the motor temp. the higher the temp. the lower the idle. Worked even better/worse after I cleaned the goop off of the feeler end, of my MAT sensor.
There is an idle air orifice (about 1/4" hole) in the top of the throttle body and an adjuster with a cap in the side. My idle air orifice was totaly plugged up. My ISS piston and seat had a 1/8th" of stuff baked on there.
If your´gonna clean the throttle body, the TPS and IAC arn´t really solvent friendly. I´ve had better results taking everything off of the throttle body and cleaning it on the work bench. When you get done, double check your Transmission Valve cable adjustment. I´ve had the best luck cleaning the ISS with my finger nail and a small tool of some type, the rod under the pston/plunger is greased from the factory, solvent is gonna wash the grease off, pulling the plunger out with your fingers can damage the IAC. Trying to run the plunger out with lectrical power, will spit the plunger across the driveway (ask me how I know this).
There is a kit to help reduce oil being sucked out of the valve cover into the intake above the TB, Moving the CCV pick up, may cause it to suck more oil, who knows? You really need the CCV, system working properly (a vacuum or as little pressure as possible in the crankcase), if the pressure in the crankcase isn´t going into the intake, it´s going to go someplace else, out the top of the valve cover, out the main bearing seals or out the dipstick hole.
While I´m passing out advice, cleaning the ground (wire brush) at the dipstick mount, the rear of the head to the firewall and behind the window washer resivoir, helps everything run better. Adding a ground from the negative battery terminal to the fender or the front clip is also a help. Time well spent. An occasional dose of injector cleaner in with the gas seems to help as does a good run up the interstate (to clean out the motor some). I idle mine way too much, it runs pretty strong, the local guys have learned to leave my old red XJ, pretty much alone, looks like a brick, but runs pretty darned good, I usually manage to leave them in a cloud of soot, at a stop light encounter. :D
 
Last edited:
Back
Top