mk2 polo injection conversion doesnt run well

[steveo3002]

abd engine that previously ran fine on carb


fitted all 3f mpi bits except the cam


starts from cold and sounds normal , quickly starts to sound rough with a unhappy idle , with the blue sender undone it runs worse ive attempted to set up the timing but unsure if the rough idle effects it..above idle it sounds better and drives semi okay



when hot it will not restart - after one hour it starts again( fuel pumps are working when it wont start)



tried 2x temp senders , new coil , ecu and (correct)dizzy works on my mates gt ,car has no o2 sensor at present, fuel pumps are running when it refuses to hot start



ive about reached the end of my knowledge and unsure what to do now

[oldskoolmat]

Youve given yourself the answer there,its the missing lambda sensor thats causing your problem!put in simple terms The ecu uses it to set the mixture.I'm pretty confident fitting one will solve your problem.

[roccoguy]

Also check for vacuum leaks. It could be that while the engine is cold and the ecu is adding extra fuel it's making it seem like it's running OK. Once the ecu starts pulling back on fueling as it comes up to temp it could he making the vac leak more apparent.

I had similar on a mk1 fiesta years ago but replace "ecu" with "auto choke", gave very similar symptoms 👍

[steveo3002]

not sure what ive done but its getting there , don't think it was going into service mode , richened it up and its sounding more like it now

[steveo3002]

udate- still need help


suffers from a bad idle,bit bumpy pop pop sound and refuses to start hot - between 3-20 mins , will start with coolant blue temp sender undone , drives fairly okay above idle

a few things ive tried /done

timing set as per the book
air bypass mixture tired various settings ...its set to 14.1 afr via a wideband gauge at the moment
tried another dizzy /cap/arm
tried another coil
correct plugs fitted
earths good
tried another tps
no obvious air leaks + charcoal can deleted
correct 3 bar pump fitted
new genuine blue sender plus tried others i had laying around
spare set of used inj tried with new o rings
spare afm tried
blocked the isv at the tb elbow- no change in running

engine basics should be fine as ive had the car driving for 2 years on a carb ..ive not touched the internals since

has crude diagnostics , no codes showing

still waiting on a ecu to try...them I'm pretty much out of ideas , anyone localish to cambridge that knows these , or a garage that remembers old cars , none of the garages ive spoke to have any ideas and don't really work on old toot

[mylittletony]

Jul 11, 2018 15:12:32 GMT steveo3002 said:

update- still need help

May 23, 2018 19:29:46 GMT steveo3002 said:

car has no o2 sensor at present

May 24, 2018 23:22:23 GMT oldskoolmat said:

You've given yourself the answer there,its the missing lambda sensor that's causing your problem! Put in simple terms The ecu uses it to set the mixture. I'm pretty confident fitting one will solve your problem.

Have you fitted a lambda sensor yet??

If not, you're curse word in the wind - They run the show (along with engine speed, temp and throttle position).

[Phil H]

May 23, 2018 19:29:46 GMT steveo3002 said:

starts from cold and sounds normal ,

car has no o2 sensor at present,

It will start from cold fine as the O2 sensor isn't used for the first couple of minutes (until the temp gauge starts to move at a guess) at which point it will think it's lean as all hell, and just keep adding fuel trying to get the O2 sensor to register, then give up as it can only add so much extra.

As mylittletony says - no O2 sensor, no go.

fitted all 3f mpi bits except the cam

..and the O2 sensor (and downpipe I assume)?

If it's a simple-ish (OBD1?) system (I'm not a VW guy) then you won't have a post-cat sensor, so the cat won't be needed BUT the O2 sensor is critical.

[steveo3002]

idles like ass from cold ..starts on the button cold

i have all the downpipe stuff and sensor now (new) will give it a try but as far as I'm aware it doesnt start off the o2 sensor from cold , not convinced and didnt want to ruin a new sensor with bad running

but yeah point taken...i will put it on and see what happens- not being argumentative but other owners report back theirs run fine without , and its a known thing to disconnect it if any issues to rule it out , but yeah i will try it

[oldskoolmat]

I would.sounds like you've spent a lot of time and potentially money up to this point.ive been around these cars a long time,and I've made many a howler along the way.once I took time to understand how the injection system works it's pretty simple really,nothing except the timing and idle you can adjust.
Fit a lambda,make sure it's got a good earth,put it in service mode and set the timing with a strobe.then adjust the idle if required.are you using the pumps and pipe from the injected car?

[steveo3002]

right

add to the list , tried spare ecu , tb and fpr ,new wires end to end from sender to ecu plug - no change

new boch o2 sensor fitted

ive pretty much tried everything i can think of , only other thing is mess with the spring in the afm which I'm wary of messing with

anyone close to cb9 would have a look , i don't think its much as just above idle its sounding fine

oldskool mat ..can you confirm how to use service mode , and should i be doing something to set it after adjustments

[oldskoolmat]

Service mode is get it up to temp and then unplug the blue temp sender.the revs will rise to 1300 rpm,make your adjustments and plug the sensor back in.
It's worth noting there are two timing marks on a polo,an "0"and a "Z".0 is top dead centre (TDC) and Z is 6 degrees advanced which is what you want.hope this helps

[oldskoolmat]

Also just check your idle screw isn't screwed all the way in,sometimes it's the simple things!

[steveo3002]

okay..what about the rev to 3k 3x...some say do it some don't , ive tried both

once its set...just re connect and turn engine off or?

the revs don't really rise when i undo it...and the idle screw wasnt so responsive in the first tb , second one works a little better, both have been cleaned and idel screw taken out and cleaned etc

yes i know on the timing marks thanks

to me its like its ignoring the set up mode or not saving the adjustments

[welshpug]

it wont be purely down to the lambda, it should still run well enough to drive around without.

[steveo3002]

yeah surprise the o2 sensor didnt fix it

[oldskoolmat]

Definitely needs a lambda regardless wether it's fixed it or not to be honest.
Well the only thing that hasn't been changed from an injection car is the cam.
Does anybody know if there is a major difference between a carb and injection cam?
Would love to come have a look but I'm in manchester

[steveo3002]

has the cam too now

[steveo3002]

right hot start was down to a relay with the pins in the wrong order , replaced that and had no probs starting so far

still doesnt idle great - and worse if i plug the o2 sensor in

getting there

[steveo3002]

sent the inj in for service /clean ...one dud , another border line dud advises to not use

getting there ...

[steveo3002]