"Stumbling" on part throttle

4109 Views 18 Replies 9 Participants Last post by jssaab, May 28, 2011

jssaab

Discussion Starter · Aug 4, 2010

Finnaly did the Injectors in the 234/235 hybrid so I could run a good tune ( thanks JZW) on the car. After adapting it runs well but I have a bit of stumbling on part throttle and before the car warms up.
I have good vac, get 27 lbs of boost tapering to 21 at 6000 rpm, At WOT I don;t notice any stumbling but I was not really trying to see if it was there., but when I am driving it "normally" it seems to "hesitate" as I get to 4000 rpm

The Sid shows no Miss ( if that is misfire)

I am thinking fuel so maybe the Throttle body?

Just for reference I did new plugs BCPRES7-11 gapped at .9, new Seimens 60# injectors and tune.

Prior to getting the new tune the car ran fine but way rich and not nearly as much power as when I first put the turbo on the old 235 engine.

Maybe I messed up a plug but would that show miss?, or somhow screwed up an injector? ( no leaks that I coudl see.

Any thoughts? thanks in advacne

1 - 19 of 19 Posts

DeLorean

· #2 · Aug 4, 2010

I'd hook it to a tech-2 if you have access to one, and see what's really going on. About a month ago, I was starting to get an odd intermittent stumble & hesitation, and an occasional pinging & lack of power when going to WOT quickly. A replacement air flow sensor corrected the problems, and it runs as good as ever again... GT17 "LPT" still going strong now @ 194K

jssaab

Discussion Starter · #3 · Aug 4, 2010

DeLorean said:
I'd hook it to a tech-2 if you have access to one, and see what's really going on. About a month ago, I was starting to get an odd intermittent stumble & hesitation, and an occasional pinging & lack of power when going to WOT quickly. A replacement air flow sensor corrected the problems, and it runs as good as ever again... GT17 "LPT" still going strong now @ 194K

Actually my thought too, jsut weird I changed ouit the injectors and plugs and now get this, but maybe its more sensitive to AFM issues now...

Thanks

BurnsSide42

· #4 · Aug 4, 2010

Sounds like the MAF - I have another issue with our 9-5 - but there are MAF symtoms present as well. When I replace the headgasket I plan to replace the MAF too. If you need one to test with I THINK i have a spare laying around.

GenuineSaab

· #5 · Aug 4, 2010

What are the A/F ratios when it is stumbling? I would investigate that. If you can look at fuel trims and see if it is staying in closed loop should be easy to diagnose. If it was a plug/ignition it would be more apparent at full load.

jssaab

Discussion Starter · #6 · Aug 4, 2010

BurnsSide42 said:
Sounds like the MAF - I have another issue with our 9-5 - but there are MAF symtoms present as well. When I replace the headgasket I plan to replace the MAF too. If you need one to test with I THINK i have a spare laying around.

I have a spare in my ohter 9-5 thanks for the offer. But yes I am thinking the ame thing

GenuineSaab said:
What are the A/F ratios when it is stumbling? I would investigate that. If you can look at fuel trims and see if it is staying in closed loop should be easy to diagnose. If it was a plug/ignition it would be more apparent at full load.

Thansks I figured fule since it does not do it af WOT, I got the A/F and it is way lean 16... so off to get an MAF i guess???

Raven18940

· #7 · Aug 4, 2010

jssaab said:
Thansks I figured fule since it does not do it af WOT, I got the A/F and it is way lean 16... so off to get an MAF i guess???

WOOAAH! Fix that shit ASAP.

GenuineSaab

· #8 · Aug 4, 2010

Start by looking at the fuel trims and airmass deviation with the tech2 before just throwing parts at it. If you have a known good AMM from any T7 car thats the best place to start. But should be able to see fuel trims and make sure the base VE mapping is close.

mike d

· #9 · Aug 5, 2010

even though the SID doesnt show any misfires, a Tech 2,, or t7suite run live though a canusb cable can tell a different story.

ive seen siemes injectors stumble before, but mostly at idle.

mike

jssaab

Discussion Starter · #10 · Aug 5, 2010

Raven18940 said:
WOOAAH! Fix that shit ASAP.

Not driving it now, its an "extra car" for the time being

GenuineSaab said:
Start by looking at the fuel trims and airmass deviation with the tech2 before just throwing parts at it. If you have a known good AMM from any T7 car thats the best place to start. But should be able to see fuel trims and make sure the base VE mapping is close.

I have set up a time to get it on tech II, to see what's up.

mike d said:
even though the SID doesnt show any misfires, a Tech 2,, or t7suite run live though a canusb cable can tell a different story.

ive seen siemes injectors stumble before, but mostly at idle.

mike

It does stumble at idle too, but "warms up and seems ok. Ther eis idle deveiaiton form 990 to 1050 RPM. I just put in new injectors. ( maybe one is bad?)

saabkid37

· #11 · Aug 5, 2010

what injectors?

jssaab

Discussion Starter · #12 · Aug 5, 2010

Seimens 630 cc... and spacers form GenuineSaab

drewz airflow se

· #13 · Aug 5, 2010

My 9k aero stumbled on boost with my JZW tune. A new DI fixed it.

mike d

· #14 · Aug 5, 2010

Drewz, on T7 cars there is alot more going on, than a T5 9000.

and misfires/low boost can be caused by a number of things

drewz airflow se

· #15 · Aug 5, 2010

mike d said:
Drewz, on T7 cars there is alot more going on, than a T5 9000.

and misfires/low boost can be caused by a number of things

I know was just throwing it out there and my car has a t7 bpc upgrade too. I just wanted to make sure he didn't over look the little things. Sounds like air/fuel issue to me.

jssaab

Discussion Starter · #16 · Aug 6, 2010

HMM just ran the car on TechII and everyhthing seems ok.

I am thinking its the fuel pump ( I have a walbro sitting at home) it has over 100K on it and the tech is telling me there was a buncha fautly MAF sensor that there is a Service Bulletin about it.

I am going to swap the MAF with mine from my 05, change out the Fuel pump ( its due anyways and i have one) get the wideband all set up and see if that helps at all...

lastaero

· #17 · Aug 11, 2010

Did you index the injectors?
If not the injectors might be spraying at the runner walls and not the inlet valves.
This is most noticable at part throttle and idle

jssaab

Discussion Starter · #18 · Aug 11, 2010

Thansk but never heard of this can you explain ( so if you ahve not guesed, no I have not)

jssaab

Discussion Starter · #19 · May 28, 2011

2

Found the issue!!!

Sorry for teh double post forgot I posted in performance:

So I posted a while back, been chasing the cause of leaning off-boost stumbling in my 2000 9=5 234/235 hybrid stage 5+. Everyone ( thank you all) said check all vac lines, did that still nothing. So today I got around to it I swapped my MAF with a "known good one" from the 03 Hirsch Aero.

It got worse, much worse.

Still figuring it was drawing air in beyond the MAF. I was thinking at the Cobra or BPV return leaking so I blew into the intake bellows downstream from the MAF and heard a hiss, it did not hold pressure... ahah! a leak.

I tried the same on the donor car and it was solid.., no leak

SO I pulled the bellows and found this!!!

Turned it over and Eureaka!

It was in the curve part of the compressed bellows, so it must have got worse when I F'd with it to get the new one in there and it was ok when curved. I had a similar issue with a split hose at the BPC one time so I was suspecting something wierd like this...

If may have gotten slapped when the serp belt went way back, but who knows?

Need to get a new one tomorrow and see how she runs, never been right since I put the engine in last year.

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