Help! FC3S Part Throttle Stumble
03-06-07, 07:29 AM
#1
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Help! FC3S Part Throttle Stumble
Newbie poster here with a problem that may have been discussed in the past. I've searched the archives and didn't come up with anything, so here is my problem.
1987 T2 - Stock motor & ecu - RB header & exhaust. About 120K on motor. Starts, idles, full power with about 6 psi boost, all seems normal. However, at part throttle acceleration, between 3000 and 3500 rpm the engine cuts off for a moment - totally. Feels like a fuel cut, not ignition, but can't be sure. Now running it with more throttle is LOTS more fun, but in traffic this stumble is a gigantic PITA.
I have a TURBOXS boost controller system new in boxes, but don't want to start with it untill I get this gremlin sorted out.
As ususal, any tips, ideas, places to look will be GREATLY appreciated.
Henry Payne
HPMotors
Pelzer SC
1987 T2 - Stock motor & ecu - RB header & exhaust. About 120K on motor. Starts, idles, full power with about 6 psi boost, all seems normal. However, at part throttle acceleration, between 3000 and 3500 rpm the engine cuts off for a moment - totally. Feels like a fuel cut, not ignition, but can't be sure. Now running it with more throttle is LOTS more fun, but in traffic this stumble is a gigantic PITA.
I have a TURBOXS boost controller system new in boxes, but don't want to start with it untill I get this gremlin sorted out.
As ususal, any tips, ideas, places to look will be GREATLY appreciated.
Henry Payne
HPMotors
Pelzer SC
03-06-07, 12:33 PM
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How are things down in Goose Creek? Used to live there myself - many, many years ago.
Anyhoo - the grounds are all clean as the motor was just installed - I've actually forgotten which injectors are on the thing - came out of a 10th anniv that got wrecked - motor was running well at the time of the accident. The 87 had a blown motor - front rotor housing was split open between the plugs. As part of ordinary trouble shooting, had the tightness checked on ground bolts, electrical connectors rechecked, etc.
Have spent a good deal of time on this so far to no avail - problem keeps rearing its ugly head. Runs fine at low throttle inputs - and runs fine above say 3500. I think something actually is being activated in that narrow 3 - 3500 range that caused the "stumble".
I hate intermittent engine issues
Anyhoo - the grounds are all clean as the motor was just installed - I've actually forgotten which injectors are on the thing - came out of a 10th anniv that got wrecked - motor was running well at the time of the accident. The 87 had a blown motor - front rotor housing was split open between the plugs. As part of ordinary trouble shooting, had the tightness checked on ground bolts, electrical connectors rechecked, etc.
Have spent a good deal of time on this so far to no avail - problem keeps rearing its ugly head. Runs fine at low throttle inputs - and runs fine above say 3500. I think something actually is being activated in that narrow 3 - 3500 range that caused the "stumble".
I hate intermittent engine issues
04-08-07, 04:20 AM
#4
Exhaust Manifold Leak
I have exactly the same problem, it really sucks, could it be something with the lambda sond or MAF? It isnt the TPS, because when i give a little throlle, at lets say 2000rpm, then is shudders, when I applie a bit more is goes fine, and when I hold that amount is begins shuddering again :/ but once over 4000rpm it really goes.. it has the knightsports big turbine turbo installed and 3" exhaust, it was tuned on the dyno and had 300bhp, but once it just started shuddering from 2000-3500 rpm at low throttle inputs..
Some input?
Forgot to say: air pump is removed..
And when it shudders it leans out, afr is going to 21.. so it isn't an ignition problem I think.
Some input?
Forgot to say: air pump is removed..
And when it shudders it leans out, afr is going to 21.. so it isn't an ignition problem I think.
Last edited by Rub20B; 04-08-07 at 04:38 AM.
04-25-14, 03:15 PM
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I got the same problem. My setup is 87TII with turboback exhaust, all emissions removed except BAC. GSL injectors upgraded fuel pump.
As soon as it gets past 4500 RPM, she does not stumble. Under medium to heavy throttle after 3000 RPM, she cuts out.
As soon as it gets past 4500 RPM, she does not stumble. Under medium to heavy throttle after 3000 RPM, she cuts out.
04-25-14, 03:34 PM
#6
isnt the 10th AE all S5 motors? i might be wrong on that.
check list.
TPS 1K resistance at idle and 5-6K ohms resistance at WOT. NO MORE THAN 6K
CAS: check the ignition timing, might be late
Vacuum leaks. spray some cab cleaner into the intake while idling. it shouldnt change. and just a "spurt" not a full on stream. if the idle smooths out you got a vac leak. if you do, take off the upper intake manifold and replace it all. costs like 45 in materials total.
check list.
TPS 1K resistance at idle and 5-6K ohms resistance at WOT. NO MORE THAN 6K
CAS: check the ignition timing, might be late
Vacuum leaks. spray some cab cleaner into the intake while idling. it shouldnt change. and just a "spurt" not a full on stream. if the idle smooths out you got a vac leak. if you do, take off the upper intake manifold and replace it all. costs like 45 in materials total.
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CaptainKRM
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