Jetronic experts - am I on the right track?
Discussion
I've been rambling in other posts on how my new to me S1 has a misfire at cruising speeds, and occasionally I convince myself that I have finally fixed it, but it keeps coming back. So I keep trying this and that when I have time, trying not to be just a parts swapper. Yesterday evening I think I found out something significant.....
When I disconnected the warm-up regulator's vacuum hose and plugged the hose, the misfire was gone. The car was more eager to cruise along at part throttle, and felt better all round except for WOT, but that is to be expected I think without the hose connected. The idle was a good 150~200rpm higher than before too. I then reconnected the hose and went for another drive, and sure enough, the misfire came back.
Here's my thinking, please let me know if you think I am on the right track: The warm control pressure is too high, and the relatively high manifold vacuum at idle and part throttle is increasing the pressure even more and causing a lean mixture. Disconnecting the vacuum hose means that the control pressure is only regulated by the springs, so it is able to drop to a level where the mixture is closer to where it needs to be, and the misfire is no more.
I have checked the resistance of the heated strip (27 ohms), measured 12V at the connector while running, looked for obstructions in the screen where the fuel enters the regulator (clean as can be). I think that a malfunction in the warm up system would actually help my situation anyway because I need to decrease the control pressure.
I know testing pressures would be the best thing, but I don't have the tools and would like to avoid buying them if I can. If I am confident that I have high control pressure, and this car ran well just a few weeks ago, then it must be a malfunction, not an adjustment problem I think. So I am trying to figure out what can cause a high control pressure. Any ideas?
When I disconnected the warm-up regulator's vacuum hose and plugged the hose, the misfire was gone. The car was more eager to cruise along at part throttle, and felt better all round except for WOT, but that is to be expected I think without the hose connected. The idle was a good 150~200rpm higher than before too. I then reconnected the hose and went for another drive, and sure enough, the misfire came back.
Here's my thinking, please let me know if you think I am on the right track: The warm control pressure is too high, and the relatively high manifold vacuum at idle and part throttle is increasing the pressure even more and causing a lean mixture. Disconnecting the vacuum hose means that the control pressure is only regulated by the springs, so it is able to drop to a level where the mixture is closer to where it needs to be, and the misfire is no more.
I have checked the resistance of the heated strip (27 ohms), measured 12V at the connector while running, looked for obstructions in the screen where the fuel enters the regulator (clean as can be). I think that a malfunction in the warm up system would actually help my situation anyway because I need to decrease the control pressure.
I know testing pressures would be the best thing, but I don't have the tools and would like to avoid buying them if I can. If I am confident that I have high control pressure, and this car ran well just a few weeks ago, then it must be a malfunction, not an adjustment problem I think. So I am trying to figure out what can cause a high control pressure. Any ideas?
Barkychoc said:
If you aren't getting much joy on here it might be worth exploring a few Ford forums (capri maybe?) where there might be more 2.8 jetronic knowledge.
Also used on a number of other cars, particularly or German origin clickySorry I can't be any more help, good luck with getting it sorted
Hi David,
It's looking like you are more of an expert than us lot on here,
I wish I could help, but my knowledge is more limited than yours.
You seem to be getting close to sorting the problem.
Have you tried googling "K-Jetronic fuel injection system"? & see if anything shows up?
I have an S1 like yours, but the only thing i've had to adjust on this system is a slight tweak of the mixture to stop hunting & cutting out at junctions etc.
Apart from that, it has been totally reliable.
If I can get any info on your problem, I'll let you know,
Good luck,
Glen
PS Where is the warm control pressure tapped from on the engine?
And what would cause it to be too high?
It's looking like you are more of an expert than us lot on here,
I wish I could help, but my knowledge is more limited than yours.
You seem to be getting close to sorting the problem.
Have you tried googling "K-Jetronic fuel injection system"? & see if anything shows up?
I have an S1 like yours, but the only thing i've had to adjust on this system is a slight tweak of the mixture to stop hunting & cutting out at junctions etc.
Apart from that, it has been totally reliable.
If I can get any info on your problem, I'll let you know,
Good luck,
Glen
PS Where is the warm control pressure tapped from on the engine?
And what would cause it to be too high?
Edited by glenrobbo on Friday 2nd November 23:49
Thanks chaps for the encouragement and links. Yesterday I took the warm up regulator to pieces, cleaned and checked everything, replaced the only o-ring, and put it back on. I did the same with the pressure relief valve in the metering head. I went for the smoothest drive ever, about 4 or 5 miles to get it up to temp. I was thinking how I would go home, grab something to eat and set out for a new pair of rear tyres, but as I pulled away from the last light, the misfire came back! Grrr!
As I sat staring at the engine I remembered that on te first day of owning the car, I adjusted the idle by using the throttle stop screw, unaware of the correct method. So I returned the screw to the previous setting and went for a drive. It seemed smooth again, but wanted to stall easily. I squirted some cleaner into the idle air hole in the throttle body and called it a day because I wreaked of petrol and had to go to dinner.
Back at it again today when the sun comes up!
As I sat staring at the engine I remembered that on te first day of owning the car, I adjusted the idle by using the throttle stop screw, unaware of the correct method. So I returned the screw to the previous setting and went for a drive. It seemed smooth again, but wanted to stall easily. I squirted some cleaner into the idle air hole in the throttle body and called it a day because I wreaked of petrol and had to go to dinner.
Back at it again today when the sun comes up!
Getting better! There was a small hole in the intake duct between the throttle body and air meter, so I patched it for now. It has more power than before - must watch for that rear end :-) The only remaining problem is the warm idle is surging from 500 - 1100 or so. I'm reading up now bu it looks like it could be a million different things!
hi loach,
just happen to be surfing and saw your post. i have a tasmin v6 2.8i and had almost the problem except mine would cut out at idle. turned out to be nothing to do with the warm up, it was an air leak.
i agree with the above post. get on to the wedge forum and ask mr zigazaga or mr tank.. they are fonts of knowledge and i doubt i would have fixed mine if werent for them.
best of luck
marcus
just happen to be surfing and saw your post. i have a tasmin v6 2.8i and had almost the problem except mine would cut out at idle. turned out to be nothing to do with the warm up, it was an air leak.
i agree with the above post. get on to the wedge forum and ask mr zigazaga or mr tank.. they are fonts of knowledge and i doubt i would have fixed mine if werent for them.
best of luck
marcus
Woohoo! It is almost perfect! It turns out that if I adjust the butterfly stop too much, I can make the misfire sensation come back, and if it is all the way back, the idle hunts like crazy. So I fiddled until I found a sweet spot and used the idle air screw to get the idle speed right. The not so perfect aspect is that when coming to a stop the revs dip to about 500 rpm or so, then climb to a stable 900 ish. With a heavy electrical load this may stall the engine.... I have checked fo intake leaks with a propane torch and found nothing, although I don't like the hose between the air flow meter and throttle body. I don't think it's leaking right now though. Any idea where to get a replacement?
I have a wide and sensor and innovate controller that I want to use to adjust the mixture, but first I need to get a bung welded onto a downpipe.
I read a few threads by mr ziga on the wedge forum and that helped quite a bit!
I have a wide and sensor and innovate controller that I want to use to adjust the mixture, but first I need to get a bung welded onto a downpipe.
I read a few threads by mr ziga on the wedge forum and that helped quite a bit!
OK, hunting & stalling, that's mixture, adjusted using a long 3mm Allen key thru the hole in the airflow meter body. Make sure you remove the Allen key after each ( tiny ) adjustment before you rev the engine. Should really be adjusted in conjunction with a CO meter for optimum setting. Clockwise for richer, ACW for weaker. It's all explained in Norman's 3rd link.
Best of luck,
Glen
ETA . I replaced my ducting with 76mm silicon air ducting from AP Motorstore. Tel +448448005199. It's twin wall, blue with orange bore, pt no.01-03064 , £24.96 per metre. Looks good & works for me! They also do stainless hose clips & self amalgamating tape. Check out their website
Best of luck,
Glen
ETA . I replaced my ducting with 76mm silicon air ducting from AP Motorstore. Tel +448448005199. It's twin wall, blue with orange bore, pt no.01-03064 , £24.96 per metre. Looks good & works for me! They also do stainless hose clips & self amalgamating tape. Check out their website
Edited by glenrobbo on Saturday 3rd November 23:49
Assuming everything is now pretty much how it was when it was MOT'd just before I bought it, the CO was 1.667%, which is high I think for the 2.8? I read that an average of 1-1.5% is about right? If so, I should lean her up a touch and see if I can fix this idle....
Edited because my brain hurts and I remembered something about the 2.8 has a CO level of 2.8%.
Edited because my brain hurts and I remembered something about the 2.8 has a CO level of 2.8%.
Edited by Loach1 on Saturday 3rd November 23:52
I hooked up my Innovate A/F wideband, just placing the sensor in the tailpipes, and it showed A/F at idle of 14.4, which is a bit lean. I richened it up a tad to 13.5. Now I am cleaned up its time for a quick spin....
Update:
It is awesome! Very smooth to drive, plenty of get up and go. There may be a slight hint of misfire, but that might just be the bumpy roads. Anyway, it isn't enough to worry about. The sun is shining so I need to make up excuses to go and tool around town.
Thanks guys for the pointers, it's good to know that I'm not alone over here.
Update:
It is awesome! Very smooth to drive, plenty of get up and go. There may be a slight hint of misfire, but that might just be the bumpy roads. Anyway, it isn't enough to worry about. The sun is shining so I need to make up excuses to go and tool around town.
Thanks guys for the pointers, it's good to know that I'm not alone over here.
Edited by Loach1 on Sunday 4th November 16:32
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