Bad flat spot

Hi all,

so I have my 1.8pf digi running and all seemed great on testing (w.o.t all the time!), i've done the setup with timing e.t.c (apart from co2) and it's pretty close but upon driving it home to store for the winter, in normal driving conditions it seems at mid throttle there is no response, as in by half throttle it surges, by full throttle no problems it'll climb the rev range without problems but on half throttle gives massive problems, i do have a small split in the intake pipe but really small (i have one on the way!), the isv valve is also giving problems (as in not working, don't know why!) but not sure if that would cause such a fault, if the isv was stuck full open surely it wouldn't idle or idle too high (although idle is turned right down) any thoughts would be really helpful, thanks

 

Until you sort out the the inlet and ISV, You can't be sure. Have you replaced the small vac lines?

 

All the vacuum lines are replaced, i have no idea whats going on with the isv, i replaced it with a generic but it made no difference, it seems i'm getting power to it but i don't feel it humming when the ignition is on?, the intake boot is really a small crack which only opens if you spread it the wrong way so i don't think it would cause such a massive problem, thanks for the reply.

 

Take a look at page 36: http://oldbluesblog.com/files/DigifantProTrainingManual_SingleSided.pdf
Should be approx 430mA accross the ISV plug at idle

The reason WOT is okay is because it activates the full throttle switch. That switches the ECU into basically "Alpha-N" mode. In other words it stops reading the AFM value and just starts spraying in fuel based on the RPM and temperature. In theory you could pull the intake boot off totally at WOT and nothing would happen.

That means that you have some issue with either air leaks (splits and ISV) or the AFM is at fault.

The ISV is only for stabilisation, the car will run without it. I keeps the idle steady through different temperatures or when the car is moving with no throttle applied. If it was stuck open, you could probably get close to the correct idle by turning the idle screw all the way closed. If the AFM CO screw was way off that could caused issues too, as there would be too much/too little unmetered air going in, although not sure how bad it would be.

 

excellent info Nate, from reading the symptoms could very well be pointing to the closed throttle switch

 

Easy to test should be continuity on the connector with the throttle closed, then nothing when it’s part way open, then continuity on full throttle too.

If that’s okay then you can do the test mentioned in the guide that involves bridging the pins

 

thanks i will test that, one thing i am confused with though is the idle stabilization control unit, does a 1991 car have one of these or is that all running off the ecu in 1991? could be a reason why the unit isn't working as i have replaced the ecu and maybe it's not designed to run the isv?

 

1991 should all be in the ECU. You mentioned it’s a PF engine, is the ECU From a PF engine too?

What was the issue with the old ECU out of interest?

 

well the old ecu had the pump fuel into the cylinders till they're full problem so bad earths, the ECU i replaced it with was out of a Passat but there was a list somewhere around which gave alternative numbers for the ecu's and it was on the list, but saying that this could very well be the problem.

 

Do you have your old ECU? And what were the part numbers, can double check for you

 

that would be great!,the old ecu no was 037906022ct, i don't have the new one to hand, would need to look in the car for that! it's a pf 1.8 8v with power steering no aircon

 

Someone will probably know more about this than me but, that ECU is listed for cars that had retrofitted cats. It has a direct replacement of 037 997 022 FX.
PF ECU's are listed as 037 906 022 FP and 037 997 022 SX.
I'm not sure what the difference is between the two engines, they used the same lamba probe. If you still have your old ECU I can repair it for you if that turns out to be the fault

EDIT: Do you have a catalyst? It might be that the "retro-fit" cars had a lambda probe fitted but no cat.
If you have one of those cars, then a PF ECU won't work properly because it's mapping won't be suited to the lack of restriction of the cat that isn't there. Which might be causing your issues?

 

I have a cat and a lambda probe from original (although both now new!) I will get the covers off the car tomorrow and see which ecu i have fitted now, thanks for your help

Edit: i found the ebay ad which is where i bought the ecu, it's no 037906722M

 

That's a Golf country ECU! Designed for the 1P/RV engine that produces approx. 98 hp. That may explain your "flat spot"

 

that could be the problem, when you have a bad earth blow the ECU (overfuelling) what does it actually kill as it seems that it is always the same symptoms, i have the old ecu here and was wondering if it would be an easy fix ie: replacing the eprom chip, i'm not much of a electronics guy but can do basic testing lol!

 

If if the injector are “stuck” on, then another thing it commonly is, is the MOSFETs which drive the injectors. They’re the packages that are attached to the heat sink on the inside, you’ll see them, have a smell around the boards too if you can’t see anything

 

O.k thanks for the replies, so i have pulled the mosfets and yes they are the culprit (traces seem o.k) but i will be buggered if i can find a replacement anywhere for them as they seem obselete, the numbers are Te2443 and Te 2383 they seem to be Motorola mosfets but i can't find any datasheets on them so have no idea what a good replacement would be, do you happen to know what perameters i would need?

edit: ok after alot of searching they are actually NTE mosfets but still doesn't really help as they are also obselete!

 

Where are you from? Are s/h ecus hard to source there?

 

not so hard to source, but expensive, and to find the right one is a bit of luck! personally i would rather fix the one that i've got now that i know that it's really just a mosfet that causes this