Hesitation under initial boost

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rossonza
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Hesitation under initial boost

Post by rossonza »

Ive taken my mr2 up and down my road ready for MOT. but ive found a problem.

she drives perfect out of boost. as i accelerate i hear the turbo building boost but the car seems to be missing, then all of a sudden it seems to make full boost and then drives great.

so far ive made a list of what to check the weekend. I just wondered if anyone had had similar before. The cars had new leads/cap/rotor arm. its got a Walbro 255. new plugs.

1. Timing (going to check timing fully on satuday)
2. Vac leak (my idle does seem to fluctuate a bit)
3. Igniton fault (i have kind of ruledt this out, as it works fine in boost?)
4. Fuel pump (same as 3, i presume its OK as once in boost its perfect)
5. AFM (plan to give this a clean with carb cleaner on saturday)
6. knock sensor issues.

I've got a boost gauge coming tomorrow, So hopefully i can see if the car is actually building boost/hitting full boost.
muckyman
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Re: Hesitation under initial boost

Post by muckyman »

any kind of aftermarket boost controller on the car?
rossonza
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Re: Hesitation under initial boost

Post by rossonza »

muckyman wrote:any kind of aftermarket boost controller on the car?


none, I've just purchased a boost gauge, but the cars mods are as following:

stock rev2 engine
stock air filter setup with airbox
brd 3 inch decat downpipe, HKS side mount intercooler
walbro 255
apexi gt exhaust

im wondering if the afm contacts could be corroded as the car was sat in a field for 5 odd years.
muckyman
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Re: Hesitation under initial boost

Post by muckyman »

HT leads?
I had similar issues on a Audi TT in the past, which turned out to be a coil pack fault...
If its been sat in a field for years, could it be old fuel in it causing poor running?
rossonza
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Re: Hesitation under initial boost

Post by rossonza »

muckyman wrote:HT leads?
I had similar issues on a Audi TT in the past, which turned out to be a coil pack fault...
If its been sat in a field for years, could it be old fuel in it causing poor running?


its had leads etc, and i drained the tank and put fresh fuel in.

i presumed the coil would be ok as its fine off boost, and find in full boost. just the middle it doesnt like.
markstevieandmads
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Re: Hesitation under initial boost

Post by markstevieandmads »

you say your running it up and down the road - are you making sure the car is normal working temp and not cold when boosting as it will hold back for this.
shinny
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Re: Hesitation under initial boost

Post by shinny »

The ECU runs in closed loop mode until about 3500rpm, and then switches to open loop. What that means is that a bad lambda could cause fueling issues and hesitation up to that RPM, after which the car will suddenly come alive and drive perfect up to the redline. I had exactly that on a rev3 turbo engine swap a few years ago.
rossonza
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Re: Hesitation under initial boost

Post by rossonza »

markstevieandmads wrote:you say your running it up and down the road - are you making sure the car is normal working temp and not cold when boosting as it will hold back for this.


She's fully up to temp. Well middle of the gauge. And that's me driving up and down out of boost. Not just idling on drive.
rossonza
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Re: Hesitation under initial boost

Post by rossonza »

shinny wrote:The ECU runs in closed loop mode until about 3500rpm, and then switches to open loop. What that means is that a bad lambda could cause fueling issues and hesitation up to that RPM, after which the car will suddenly come alive and drive perfect up to the redline. I had exactly that on a rev3 turbo engine swap a few years ago.


Did you get an eml? Or any codes thrown. I'll have to check the rpms
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Ryan S
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Re: Hesitation under initial boost

Post by Ryan S »

rossonza wrote:
shinny wrote:The ECU runs in closed loop mode until about 3500rpm, and then switches to open loop. What that means is that a bad lambda could cause fueling issues and hesitation up to that RPM, after which the car will suddenly come alive and drive perfect up to the redline. I had exactly that on a rev3 turbo engine swap a few years ago.


Did you get an eml? Or any codes thrown. I'll have to check the rpms


you may not get a code for a knackered o2 sensor.
rossonza
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Re: Hesitation under initial boost

Post by rossonza »

Ok thanks guys.

Will get my friend to eyeball the revs during the hesitation on Saturday :-) will update the thread soon.
shinny
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Re: Hesitation under initial boost

Post by shinny »

Ryan S wrote:
rossonza wrote:
shinny wrote:The ECU runs in closed loop mode until about 3500rpm, and then switches to open loop. What that means is that a bad lambda could cause fueling issues and hesitation up to that RPM, after which the car will suddenly come alive and drive perfect up to the redline. I had exactly that on a rev3 turbo engine swap a few years ago.


Did you get an eml? Or any codes thrown. I'll have to check the rpms


you may not get a code for a knackered o2 sensor.


I got not EML and no code...
rossonza
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Re: Hesitation under initial boost

Post by rossonza »

shinny wrote:
Ryan S wrote:
rossonza wrote:

Did you get an eml? Or any codes thrown. I'll have to check the rpms


you may not get a code for a knackered o2 sensor.


I got not EML and no code...


Ok sounding likely then. Found a lambda on eBay. Denso. £75. That sound about right?
shinny
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Re: Hesitation under initial boost

Post by shinny »

For the branded part, £75 sounds reasonable. There are probably cheaper ways to get a functional lambda.

Edit: Your rev2 engine probably has a 1-wire sensor rather than the 4-wire sensor you'll see listed for many MR2s
rossonza
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Re: Hesitation under initial boost

Post by rossonza »

shinny wrote:For the branded part, £75 sounds reasonable. There are probably cheaper ways to get a functional lambda.

Edit: Your rev2 engine probably has a 1-wire sensor rather than the 4-wire sensor you'll see listed for many MR2s


yes thanks mate, id been looking at rev1-2 sensors. £75 was cheapest i could find. mr2 ben had them for £85.

just trying to source a 2nd hand one just to test if its the issue before spending my hard earnt £ on a sensor. yes im that tight. :D
rossonza
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Re: Hesitation under initial boost

Post by rossonza »

So..... My friend Steve came over today and we did the following.

1. Checked ht leads continuity (found a dead lead so I've put an old lead back on)
2. Re gapped plugs and checked them (they were really black)
3. Adjusted the TPS
4. De lidded afm found no corrosion but gave it a clean and re sealed it

She now runs great. And blipping off the idle was much better after the tps was adjusted to spec with a feeler gauge.

Slight hesitation around 3k rpm. But it's so slight now it's barely noticeable. Planning to MOT the car and give it a good run. See if it helps with the smoothness.

Whilst driving we noticed a clunk behind us. Turns out I hadn't done the front engine mount up tight..... Oops. So went round the car tightening all the bolts/engine mount bolts. Luckily all were tight. So must have just missed the front.

Surprised my friend with how fast it was. I accelerated and he said ahhh it's pretty quick then it came on boost :pray:

Thanks for all your help guys. I'm hoping the mot emissions test will tell me if my lambda is broken before spending £75 on a new one
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Ryan S
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Re: Hesitation under initial boost

Post by Ryan S »

Good stuff mate!! Just chuck a cheapy o2 sensor in the now to rul it out :thumleft:
rossonza
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Re: Hesitation under initial boost

Post by rossonza »

Ryan S wrote:Good stuff mate!! Just chuck a cheapy o2 sensor in the now to rul it out :thumleft:


Cheers mate. Wasn't sure if I could. As it's got that metal around it to bolt it in.
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Ryan S
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Re: Hesitation under initial boost

Post by Ryan S »

Ah!! I'm not actually sure now you've said this!
rossonza
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Re: Hesitation under initial boost

Post by rossonza »

Ryan S wrote:Ah!! I'm not actually sure now you've said this!


Yeah I'm sure when I fitted the decat downpipe it had a metal collar which is part of the lambda. Oh well it seems cured now... I'll get it motd and give it a good drive. See how it feels. :thumleft:
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