car = 74 1.8 L jet (all intact).

problem =
out driving this morning - gradual then worse loss of power. no accelerator response.
pulled over. cut out. no idle. let it sit for a few minutes. restarted it. got it going.
got up road all right, but symptoms kept coming back, then going away. limped it home.
fun ruined for driving, but fun diagnosing started.

felt like your classic fuel starvation.

background. car has been recommissioned and back on road for about 5 months.
running beautifully.
fuel system entirely rebuilt. clean tank. new fuel lines. new fuel pump. new injectors.
all vacuum lines renewed. all ignition compenents renewed. except coil (which could be original, looks like it, but coil was tested and was a goody).

one thing = fuel smell in engine bay on lhs around air cleaner. comes after a few days sitting. had put this down to saturated charcoal cannister, feeding back fumes into aircleaner. have inspected all fuel lines etc thoroughly and no signs of any external fuel leaks/wetness. just a vapour smell thats not there all the time, just after sitting.

pulled everything apart today down there after getting home today.
checked everything. all tight, no air leaks. no bad hoses.

looked at pressure regulator. which sits right there under aircleaner.
i have no reason to think its not original and about 45+ years old.
and did not get replaced. looks great externally, but.........internally?

will get car into shop this week. where i can get some guages on it etc.
at home with car. nothing but basic tools.

but whats thoughts out there.
anyone had this one before.

Test the fuel pressure on the port on the drivers side fuel rail. 28-32 psi is normal Pressure regulators do not go out often.

2 @wonkipop

Test the fuel pressure , I use a longer hose and tape the gauge to the rear window so I can drive and watch the gauge in my RVW.
One thing your symptoms may suggest is the under tank fuel hose is collapsing. From under the car remove the rack service plate and there's a hole you can get your hand up through under the tank. Feel the lines one bend a hose may feel slightly collapsed, but not fully. This hose likely is collapsing and can do this even after 15-20 minutes of trouble free driving.
In this case you would have good fuel pressure then suddenly you have zero pressure.

Good luck with your hunt.

Check your dual relay, under the battery tray. Unique to 1.8s, I believe. Took me a year to figure my cutting out/ restarting issue.

thanks for the tip.
reading up on 1.8 injection control now - realising not like djet re fuel pump control etc. still things to learn every day with a 14.

@bdstone914
only reason regulator on my list is the car sat for 16 years. all got replaced apart from it. diaphram might have failed because of bad treatement from me.

@Mark Henry
thought that. but am thinking pump. put the tank hoses in carefully with excess for relaxed looping. not easy to inspect from below on my car - its rhd! port is not there anymore. flex lines in and out of pump concern me - replacement fuel pump is in original location under engine but in line pump. hasn't emerged as a problem if it is until now. but its on my list.

have to get the gauges on it - can't do much in the garage at moment.

doing the check up one step at a time.

got the car to the workshop today, got there without power loss, but the idle was hunting, not badly, just 850 - 950 on the tacho. up and down. it cut out once at the lights just as i got to the workshop after a 20 minute drive.

we hooked up guages to the fuel system. did a pressure and delivery check.
pressure gauge on the injector side of the pressure regulator.
fuel flow on the outboard side of the pressure regulator.

eliminated fuel pressure and flow as well as pump and pressure regulator from equation.

pump gives 39-40 psi, no vacuum - measured with gauge in front of regulator.

delivers 850ml in 30 seconds after the regulator.

we get 32 psi at 18 inches of vacuum.
35 psi at idle with airflow meter on.
30 psi at 3000 revs.

we figured the hunting was a sign of an incorrect mixture.
reset the points, they were a bit dirty, but not overly. i mean i used to run VWs in the 80s on worse, way worse actually, but we cleaned them and reset the timing.

adjusted the idle to about 1000 just to give it a bit more.

wriggled and moved every single vacuum line and could not make it change idle or react.

then i went out and thrashed it by the railway lines for about an hour.
fun. redlining 2 gear and 3 gear. have not done that for a while. not that a 1.8 is going to give you whiplash, but it was very pleasurable winding it out. was thinking wouldn't it be nice if that was a 917 motor i was hearing.

i could not upset it and make it do what it did yesterday.

drove it back home at days end without incident.
seemed to make everyones day in post covid lockdown peak traffic.
folks were waving at me. i was thinking the car was on fire.
they were just waving.

so something upset it, and i can't believe it would be the points.

one step at a time.

we have eliminated the fuel system and the spark delivery.
the coil seems fine, despite its age.

we will move on to more electronic items like sensors.
have to wait for it to come back.

calling mr. perrine / or any 1.8 guru.

@ClayPerrine

i've been able to induce the fault, got a pattern.

start car cold and it as it warms up it comes up to steady idle and stays stable.
car revs cleanly, drives cleanly.

switch off when hot and leave it for a certain amount of time, roughly 10-15 minutes and it restarts in idle hunting mode, 500-850 rpm up and down and won't come out of it.

i tripped over this yesterday when i was going over every vacuum line and square inch of intake plenum, intake boot etc. it started happily and idled away happily for 15 maybe 20 minutes while i was checking for leaks. i switched off to make a coffee and take a break, about 5 minutes. restarted it and it went into hunting mode for maybe a minute, then settled down to steady idle. thought - interesting! - so switched off and left it for just over 10 minutes and when restarted it went into idle hunting idle mode and would not come out.

left it for around 6 hours and started it before going to bed. started up fine from stone cold and settled into steady idle. let it run for 10 minutes or more until it got warm. stayed steady. turned it off.

today i managed to repeat the fault induced yesterday with the same pattern.
started cold fine and came up to steady idle and sat happily. switched off and immediate restart, idled happily. switched off and left for 5 minutes, started with a stumble and about i minute or less of hunting and then settled into idle, could not induce any misbehaviour by some revs etc. turned off and left for 15 minutes and restarted it went into hunting idle mode and would not come out of it.

figure i should go into component testing mode next. sensors etc?

have eliminated, fuel pressure, timing, points, spark and i believe any vacuum leaks as causes.

on off chance anyone has struck this before any pointers might help.

its pointing to some mixture problem at idle and possibly under power, but i haven't been able to make the under power situation occur, did not take it out for a drive after inducing hunting idle.

realised i might have had this problem for a while but not noticed as particular behaviour makes it happen. starting it after a certain period of time has elapsed after hot shutdown and before its gone cold again. been just driving it for the last couple of months with a start up and early morning drive once a week where i don't switch it off - just drive it, have fun and park it back home. what i had done last sunday was take the car out, but i left it in the street for about 10 minutes between getting it out and going for a spin. the fault emerged soon after i was down the road after the restart.

think i cracked it this afternoon.

did some work at afternoon tea break.
pulled down the intake to the throttle body junction with plenum.

nothing obvious there, i had detected no air leaks with hose or cig smoke previously.
but come to think of it i had not been doing either of those things while it was in fault mode, i'd been listening for leaks after it had got to a stable idle situation the times i had gone over it.

i did three things only.

i cleaned interior of throttle body, slight little pool of oil from pcv valve hose.

and i pulled out the throttle plug which was lightly coated in oil and cleaned it.

and i thought how did that oil get there.

i found one of the screws holding the throttle body to the plenum was loose, but when i say loose, i mean barely loose. it turned maybe half a turn with screwdriver to tight, the other one was tight. so backed it all off, cleaned cone gasket. put it all back on square and tensioned it up evenly. i noticed that the gasket/joiner was maybe starting to go hard, (its been 46 years!).

i cleaned the tube from the aircleaner to the throttle body throughly. i gave it a look over with a magnifying glass. its still flexible. like factory fresh. no cracks.

so i put it all back together.

put it through the regime i had done earlier and the fault is gone.
no hunting (ok some, but very minor and i put that down to the adjustments done on monday to stabilise the idle, and the settings now need to go back). it comes up to even idle after fully warmed, no hunting or carrying on.

since then been out, started it every 20 minutes or so. let it come up to temp.
turn it off. done it 6 times - fault is gone. this would have induced the fault given what i had done over the last two days to work out how to make it happen.

so its down to one of three things or all three.
1.throttle switch connection dirty with oil.
2.cone gasket between throttle body and plenum leaking air at certain point of expansion and contraction in heat soak cool down phase after switch off.
3.there was an air leak between air duct hose from air cleaner and throttle body.

i'm going for #2 and searching out a new cone gasket/joiner for the throttle body air plenum junction.

i think what has happened is that particular part maybe has hardened up.
and engine vibration etc since recommissioning has caused one of those tensioning screws to back off and loosen enough to upset it. not much, but enough it seems.

if #2 is what it was it proves how sensitive L jet is to leaks (super sensitive) and that those leaks won't necessarily be there when its cold or when its fully hot. but they might develop at a moment when the two materials expand or contract differently during a cool down phase.

i'll be driving it out on the road to the workshop tomorrow to reset the mixture, so i will see if this holds up on the road tomorrow.

Okay so if I understand correctly, we have two conditions here: car dies randomly after warmed up, and a idle hunt?

I wouldn't eliminate the fuel delivery system just yet, it can be dropping out intermittently from the contacts inside the AFM or dual relay. Where is the fuel pump located in your car?

You replaced the fuel injectors, what did you replace them with? I suspect a lean condition or too much advance on the dizzy that might be causing the hunt. You need to verify timing again, and it might be time to invest or borrow an air fuel ratio gauge to see where we are at.

i will take it out for big test drive today to workshop to see if it can be induced driving.

will be resetting dist and timing there - we fiddled with it on monday.
doing a check of the ECU plug and relays AAmeter CHT sensor etc..
have an L jet diagnostics manual now and the EFI circuit diagram.
will finish what i started to be 100% sure.
i know all the mech parts of the fuel system are delivering, so a fault if still there, is probably in the controls as you say.

got the gear, air fuel ratio guages, even exhaust gas analyser out at workshop.

one of our members here has kindly offered to send me down a new cone gasket for the throttle body from brisbane. very nice of him and communication was unexpected. members here look out for each other even in this far off corner.

i see 914 rubber make this valuable little part.

i realise its time to get a spare of all the EFI components in a box. one of each.
have noticed there are real difficulties obtaining an AAvalve.

i'll confirm what i think was going on after today.
the longish drive to the workshop followed by a shutdown and restart roughly 10-20 minutes later will either confirm it was the throttle body and cone gasket or it is a gremlin still in there. if the fault persists i seem to have found a way to induce it and test while its faulting if it comes back. but even a repeat late last night of the start up exercise seemed to have indicated its gone. touch wood.

injectors were replaced with a set of bosch injectors (still sealed in plastic bags and boxes with nozzle caps) i bought last year. from a vw guy in colorado. original correct parts. injectors are good, we tested them before install about 9 months ago.

the cold start injector was not replaced, it was working, but its on my list today to take a look at it and ensure its not leaking.

the fuel pump is located in the under engine position up under the chassis rail spot (factory 74). i don't think its vapour lock, or collapsing lines, checked all that on monday. been running the car for 7-8 months now and on hotter days and for longer distances than for what has been going on now without problems when driving. the pump is new. the only sign of vapour lock is occasionally after shut down it takes longer to crank for restarting. but it does not, not start, on the first crank. usually start is immediate, but on those occasions it can be 5-6 seconds of cranking to fire.

we know we are getting fuel down the lines from the tank with good flow, pulled them off to check just to be sure when we did the pressure flow test on monday. checked the return line.

to be clear, the car does not die randomly. it died during the first episode of the "condition". when this first appeared on sunday it was during driving. the throttle was hesitate and the engine failed to deliver power and rev cleanly, i pulled to the side of the road and was giving it the gas to try and keep the engine going, it died as it came down from revs, or failed to settle at idle. it restarted straight away. and drove. but did it twice more before i got it home. one thing i'll say for L jet, it tries real hard to make the engine run even when it does not want to.

i'll know more after today.

it looked to me yesterday like the throttle body was in the early stages of working itself off the plenum. one of the screws took a quarter turn. the body was 1 mm further out on one side than the other. normally i would not have thought that was a problem as for all intents and purposes it was "tight". i think with a cone gasket in good "as new" condition it would have been sealed. i'm guessing that at certain times it was sealing and at other phases of thermal expansion it was opening up. i'd had it all apart about 9 months ago during recommission and had put it all back together carefully then. seating it evenly. so it had definitely moved since then. not by much but it had moved. i'll know more when i take the gasket out, which i don't want to do until i have the replacement to go straight in.

The aux air valves tend to be a unicorn part for our cars. I just recently bought a new one for some 90's nissan sentra pn# AC369. It does mount correctly, the closing times are very identical, but the connector has a tab in the wrong place. So a bit grinding will be necessary, or get a pig tail that fits the new valve will be needed.

I still think you are running lean or too advanced and running hot. The AFR gauge will paint a better picture. I wonder if they still sell those oil thermometer dipsticks?

thanks for tip on AAvalve.
be nice if i can pick one up here.
i see 944s had same valve so we might be able to ask around and see what folks are doing for those locally.

definitely was a running with wrong mixture problem for sure.

see if i got to the bottom of the cause with a bit of work on it today.

i remember those dipsticks. vintage item? a lot of vw mechanics had them.

i only had time today to attend to the Aux Air Valve.

moved a few of the charcoal can lines out of the way before the drive out.
discovered the hose between AAT valve and intake plenum appeared to be collapsing. once out at workshop gave it some revs while i watched it and it distorted into a wild shape, however the car was warm and pulling vacuum at revs.
cold it was definitely partly collapsed in the bend between the valve and plenum. might have been affecting draw of air during warm up? this was hose that porsche aus supplied us. we shredded the original getting it off 9 months back. i did a trick with it that might have worked, sometimes doesn't, but a couple of hose clamps are helping it keep its shape under vacuum. might look around for a better hose.

pulled the AA valve - its fine. fridged it - opened right up. test wired it to a battery and got a 100% close. took about 3 - 4 minutes to close from room temp state. tested connection and its getting current. gave it a cleanout with carb cleaner inside. it looked clean in there before i did that anyway. nothing sinister came out with the clean.


far as i took things. do one thing. drive it, see what happens, on to next.

we did not play with timing. left it alone as set it on monday.
want to wait until i install a new throttle body gasket.

hooked it up to the EG analyser but its got to be serviced - could only take CO readings. coming in at 2.3 % CO. i can borrow an EG from across the road guys, but they were busy today.

its driving nicely fully warmed up, but still little moments, one or two where it goes into a slight very minor hunt on the way back home pulled up at the lights. its idling ok at about 900.

something still there niggling it.

but its a lot better.

i'll move on the CHT sensor next and test that.

after that go through the brain plug tests.

test tomorrow when its stone cold will be to see what it does during warm up phase.



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just been on a 340km round trip run up country to euroa for the weekend.

getting much closer to sorting out the problem.
several problems intersecting at the same time?
unsurprising - its been recommissioned after 16 years sitting.

1) i've got rid of the cold start warm up issues.
think it was two things going on leaking air after the AFM flap.

one - throttle body. hopefully new throttle/plenum gasket fixes that long term - in the short term its stayed tight.

two - a collapsing hose from Aux Air Valve for cold start.
i've rigged that so it does not collapse with hose clamps.

result three perfect cold starts in the mornings (one of them reasonably chilly for southern australia at the start of autumn out in the countryside) - no hunting no fuss.

2) i've still got the almost dying and uneven hunting idle but occurs only under the following conditions.
caught in stop and start traffic, on hot/warm days.
listening closely i can hear the fuel pump struggling, making noises, changing pitch.
fairly sure the culprit is the mild steel fuel lines i have run down the tunnel and the section leading from firewall exit to fuel pump. sitting in traffic the car is sometimes sitting in its own hot air and its building up under the car in certain circumstances.
both times on the trip up and back i had the problem at the same spot leaving the city and coming back. a long sequence of about 6 traffic lights with long lines and delays at the lights.
i'm going to try and insulate the lines to protect them from the heat build up.
the fuel is maybe boiling in the line section in front of the pump making the pump cavitate and struggle to make pressure in those conditions?
- think you are right @timothy_nd28 , the fuel delivery is getting in the focus again.

good news.
its been at least 20 years since the car has done a good long run.
it got it.

out on the "interstate" it keeps on winding out.
i took my eyes off the speedo a few times and it was running up to 90 mph comfortably on its accord - turbine smooth, had forgotten what this car was like at speed cruise.
(in australia sadly that would mean instant loss of license and car impounded if the cops got you in the radar gun or pole cameras - so i had to start being careful after i let it happen a few times).

happy to sit and cruise at 70/75mph all day long.
run up through a great little back road twisty enscarpement climb with lots of sharp corners.
no coughs, no stumbles.
gave 8.9L per 100k or in usa-speak 26/27 miles per US gallon.

getting used to the thin michies, feel good on second rate little country roads with uneven pitching surfaces.


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Been chasing similar fuel supply funkiness on a friends car. We had replaced the fuel lines and found that one under the tank was slightly bent and collapsing. Was causing really intermittent and random fuel starvation issues. Even when you think these are perfect, it's always worth triple checking.

interesting. i can't discount it either now.

90% sure its on the tank side of the pump given struggles i can hear from the pump when it is having the issue. so the fuel tank line will have to get looked at. the villain is in there somewhere.

Here is a vid of my 1.8 L-Jet testing from a while back.

https://youtu.be/dVjk0a0zk4s

AFR Testing

https://youtu.be/owYGugwTguE

Pete's way of monitoring fuel pressure is outstanding!

yes, the clips are great.
thanks for that.
the phone app EG readout i will be investigating immediately. too good.