Can A Slightly Erratic Idle Be Caused By A Bad Fuel Pressure Regulator

[lee.kendallmi16 2]

Basically same question as what's in the title.

 

Can a slightly erratic idle be caused by a bad fuel pressure regulator mi16.

 

I've changed loads on my peugeot 205 1.9 16v mi16 to get a pretty solid idle. Seen as one of these things was refurbish the AFM I was then unsure what my emissions would be like but I thought engine was running rich.

 

Took her in today and engine was running rich 9.5% which they managed to get down to 2.5% with an idle between 1k RPM and 1100 RPM but now the car seems to be more erratic on idle and is hesitant when I drive it and let my foot off the gas.

 

It doesn't stall at all just lumpy running.

 

It's had a new fuel filter but I'm thinking could this be the cause of a failing pressure regulator, as if the pressure isn't there properly.

 

Does anyone have the part number of the fuel pressure reg I need?

 

Any thoughts guys.

 

Thanks for any replies in advance.

[jackherer 543]

I've never known an Mi16 fuel pressure reg to fail. I'd guess your problem is due to wear in the throttle body.

[Anthony 1,003]

They don't tend to fail as such, but there can be a significant difference in the pressure that supposed identical units will hold the fuel rail at and thus the resulting fuel-air mixture.

 

I remember diagnosing why Kyepan's old Mi16 never felt as lively or produced the power figures that it was theoretically should have - checking on the rollers the AFR's were a bit lean and, after trying the usual things, we checked the fuel pressure and it was only holding at something like 2.6 bar at WOT. Swapped the regulator out for a spare I had, and it was holding much nearer 3 bar, increasing power and responsiveness.

 

Had an 8v (same FPR) that was very flat which was fixed with a replacement FPR too, although I never measured the actual pressure on that one.

 

I would imagine that it's plausible that one could be holding excessive pressure, leading to over-rich mixture (high-ish CO) and a crappy idle. Other things that could cause it though, as above.

[lee.kendallmi16 2]

I've changed the throttle body because the last one i had did have wear on the seals but when the old one was fitted the car stalled all the time when approaching junctions etc.

The car doesn't show any signs of wanting to stall what so ever, that's why I'm thinking it could be related more to fuel side of things now.

 

Up to now I've done the following:

 

Refurbed AFM

Changed TB for known good one

New coolant sensor

New dizzy cap and rotor arm

New throttle position sensor

New coil

New ICV (bosch)

New k&n air filter

Service inc plugs, fuel filter etc

 

Can anyone tell me why, when I'm driving and picking up speed, at around 3500/4000 RPM, I get a sudden surge and the car wants to take off. Should it not be this responsive all the way through the rev range and not just when it hits mid RPM range?

[jackherer 543]

Can anyone tell me why, when I'm driving and picking up speed, at around 3500/4000 RPM, I get a sudden surge and the car wants to take off. Should it not be this responsive all the way through the rev range and not just when it hits mid RPM range?

it's hard to say for sure without experiencing it first hand but that sounds like a normal Mi16. As long as it's not completely flat at low revs its usual for them to pull much harder from about 4k.

[lee.kendallmi16 2]

Ok cheers.

 

It's not flat at low revs and goes well apart from the slight juttery hesitation whilst picking up speed from low revs.

It's like it could be misfiring.

 

Just not sure which direction to head in and check/change next.

[jackherer 543]

That sounds like it could be an ignition amp problem, does it ever hesitate/misfire at 3.5/4k before it picks up?

[lee.kendallmi16 2]

Not that you can tell whilst accelerating when driving it but if you have the car stationary and rev the engine slowly through the rev range it will start to make popping noise/misfire around 3500RPM then if you keep going passed this it will clear and become normal again. So it's actually only making this popping/erratic running at idle and the popping noise from exhaust again when revs reach around 3500.

[jackherer 543]

Its definitely worth checking it's a proper blue Bosch one with MTR 01 on it and if it is taking it off the heatsink plate and giving it a cleanup and some new thermal transfer paste.

[lee.kendallmi16 2]

Ok I will take a look at it. If I remember rightly though it is black on mine.

I'm no mechanic but have a little bit of knowledge.

 

What exactly does the ignition amp do and why would it cause this problem.

 

Cheers for all the replies.

[jackherer 543]

If it's black that's not a good sign, they only really run right with the originals IMO.

 

The ignition amp is basically some transistors that amplify the small current from the ECU into a larger current to drive the coil. If it fails or overheats due to bad paste between the amp and heatsink the coil wont spark everytime, i.e. a misfire.

[lee.kendallmi16 2]

Ok will look as soon as I'm off these daft nightshifts.

 

Thanks again.

[welshpug 1,657]

Did you re-set the throttle switch?

[lee.kendallmi16 2]

I reset the throttle switch after changing old for new but I haven't touch it since garage played with TB and AFM

 

Why could this now not be setup correctly?

[welshpug 1,657]

If the throttle stops have been fiddled with you need to check it is set correctly, as it could be either not getting the off signal, or the opposite could be stopping against the switch and not reading WOT.

 

Either could cause the stalling.

[lee.kendallmi16 2]

Mine is not showing any signs of wanting to stall either at idle or when driven.

It is just running lumpy at idle, possibly misfiring.

[lee.kendallmi16 2]

Hi guys,

 

Just removed my blue bosch ignition amp and found that there was no thermal paste between itself and the aluminium plate.

 

I've cleaned the faces up and applied thermal paste but the misfire is still there.

 

Could this have knackered the ignition amp altogether?

 

Also I removed the vacuum pipe off the FPR and ran engine for a while to see if it wasn't holding pressure and passing it down into the inlet but this seemed ok.

 

Any other suggestions?

[welshpug 1,657]

I don't think this blue colour is particularly relevant, most I have seen are black or grey and have been o.e parts.

 

It is possible that it has been damaged if there has been no paste behind it, though it would have needed to get pretty warm.

 

I have a collection of Intermotor and Bosch and they all do the trick fine.

[farmer 328 1 Cars]

I don't think this blue colour is particularly relevant, most I have seen are black or grey and have been o.e parts.

 

It is possible that it has been damaged if there has been no paste behind it, though it would have needed to get pretty warm.

 

I have a collection of Intermotor and Bosch and they all do the trick fine.

 

All my O.E ones I have or seen are blue in colour

 

I have some new ones coming to me in the for sale section.

 

Intermotor are crap !

[lee.kendallmi16 2]

Ok cheers I will keep you in mind for a new amp, but before buying one I could do with ruling out everything else first.

 

It would be better if I new someone with an amp around my local area (barrow in Furness) so that I could try another known good one but there ain't many around.

 

I've just had my injectors out to look at the spray pattern and to see if any leak fuel but the pattern seemed ok and they weren't dripping. If anything it looked like each time I cranked the engine over one injector would be weaker than the others, but it did it with a different injector each time so it might just be me.

I've noticed the seals looked abit worse for wear (old) and one of the ones connecting to rail was letting fuel passed if you wiggles it. Upon further inspection it had a cut out of it.

 

Can bad injector seals cause misfires and if so why? They don't leak fuel when running.

[farmer 328 1 Cars]

I just sold my spare one or would have sent you one down to try but let me know if you want a new one.