Losing Significant Power When Driving (Idle is OK...) - 8V Digifant

[cox]

Hi,

I am having a problem with my Mk2 Golf GTI (1990 Digifant) significantly lacking in power (pretty muich making it undrivable on Motorways and A roads). I decided to give rubjonny's Digifant tuning guide a try and the car is idling nice and smoothly but it is still down on power when I take it out for a drive.

I took the car out for a drive and it managed about 50mph going up a slight hill in 4th gear with my pedal to the metal. When I got to the top of the hill I felt a bit embarrassed, pulled off the main road and then drove back home (managed to hit 60 going down the hill though!). Regardless, something is up, it kind of takes a while to pick up power (kind of like turbo lag without a turbo) and I am having to rev higher than usual to get any decent speed (although 3rd gear doesn't feel too bad, neither does 1st, 2nd is very sluggish as are 4th and 5th). I had the valve stem seals changed recently, but don't think it is that as I drove home from the garage fine, I just noticed the idle was a bit rough, so adjusted the idle, but I think altering the idle/mix has just fixed the idle and masked another underlying problem.

I did a bit of diagnosis, but I can't see any obvious problems (added pictures just in case they help other people having a similar problem...)

1. I disconnected the blue temp sensor and the engine was running a bit rougher than with it connected, so it seems that the temp sensor is working OK.



2. I disconnected the ISV ( Idle Stabilisation Valve ) and the engine started running a bit rougher, so again, this would suggest that the ISV is working. It also vibrates when I turn on the ignition and I removed the breather hose and tried blowing into it while the engine was warmish (50 degrees) and air was flowing through it with a bit of resistance, suggesting it isn't stuck open/closed.



3. I disconnected the AFM (Air Flow Meter ) connector and the engine struggled for a few seconds and then cut out, again, suggesting the AFM is OK (I have also highlighted the AFM adjustment screw I used to change the mixture as per rubjonny's tuning guide).



4. Finally I checked what I think were the vacuum hoses (the ones that connect to the green bit of plastic and then to various other places). I also checked the breather pipes, but couldn't see any obvious signs of splitting/leaking. The top of the big hose that connects to the AFM/Air filter looks OK, but I will need to take it off to examine it properly.



5. And here is a picture of my engine just for reference (just in case I need to point out anything else)



I was just wondering how can you tell if there is an air leak and would it have to be pretty substantial to have that kind of performance decrease on my car? Like I said, I am just visually looking at the hoses for slitting, etc, but I am not sure exactly which of the hoses I should be checking for leaks. Also, does anyone else have any other suggestions as to what I can check? I think I have carried out the most obvious checks and like I said, I have been through the co/idle tuning part of rubjonnys guide as well.

Thanks,

Dave. 

[mk2bal]

Have you checked your timing? If you did stems I'm guessing the belts been off at some point.. Don't forget you don't set any advance on the digi's, the dizzy should be set on tdc with top and bottom pulleys, the ecu does the adjusting. I'd say that's probably your 1st port of call for lack of responsiveness.

[cox]

Hi mk2bal,

Many thanks for the reply. Do I just need to check the timing using a strobe light and adjust the distributer accordingly (as per page 143 of the Haynes manual) or do I need to do anything else?

If so I will need to invest in a timing light!

Thanks again,

Dave.

[mk2bal]

I think ignition timing is in the guide, I meant check the belt for tdc top and bottom marks being bang on first. I think the ecu does all the advancing on the digi, so not sure if you adjust the dizzy too much, may just need to use a basic strobe without advance and go from there. The guide should cure any probs or highlight faults.

[mk2bal]

Just re-read your 1st post and it seems like you've checked over the basics with the guide etc, I know carb cleaner can help find air leaks as it can cause the engine to rev up or down, but don't think that applies to vacuum hoses, mainly intake hoses etc.. Check your cambelt for timing,and if its out then re-set it, and follow the guide again.. I'm sure once you've confirmed all that someone a bit hotter on digi will come along, I'm a 2.0 16v kjet man myself, can only help you with the basics!

[swampy50]

Possibly lift pump on its way out ?... Thats what mine was when I had similar symptoms..