How to find small vacuum leak with A-tap??
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From: The Confederacy
How to find small vacuum leak with A-tap?? My car is acting REALLY weird. It idles and pulls good, but when I try to cruise down the hi-way and maintain a low speed, it hesitates and misses sometimes. It is just while you "hold" it at a certain speed, if you give it gas.. it smooths out and pulls fine. If you put it in neutral and try to hold your foot on the accelerator and keep the RPMS around 1,600 or so.. it just won't do it, it surges up and down. It is only around that RPM range 1,600 to 1,800 rpms and at a "holding" spot on the accelerator or as soon as you give it some gas. I have had the intake on and off the car 8 or 9 times and all I can think of is that one of the o-rings between the intake and the heads is sucking a little air or something. What could I look for in a-tap to tell me this. My Ltrims are pretty close to 0 while idleing, but when I accelerate they go to +10 to 13 or so. When I hold it or cruise around the RPM range it acts up.. they go slightly negative. Any input would be appreciated.
Thanks
Scott
Thanks
Scott
A vacuum leak shows up mostly at idle.
A hard miss that rapidly comes & goes like you describe usually is ignition.
What are the O2's doing when it surges?
Surge can be lean, is the car tuned?
A hard miss that rapidly comes & goes like you describe usually is ignition.
What are the O2's doing when it surges?
Surge can be lean, is the car tuned?
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Joined: Nov 2001
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From: Farmingdale NJ
Could be a dead spot on the throttle position sensor. With the car on and the engine off, pull up the TPS voltage and/or position in % on AutoTap or similar. SLOWLY go from idle to WOT. Should spend a good 20-30 seconds completing the full pedal travel. If there is any jump, dip, or flat spot in the TPS readings, replace the throttle position sensor.
It's a long shot but worth a try before you go taking a bunch of crap apart again.
Did you connect the hoses on the back of the intake?
Also, did you properly torque down the intake bolts? They require very light torque (100 in/lbs I believe) and if they're over tight it could cause distortion, thus letting in air.
You can also try spraying really soapy water (I use dishsoap) around the intake and TB anywhere there is a mating surface. It should foam up nicely but if there is a vacuum leak the bubbles will collapse. The idle will probably surge a bit too if you spray the spot that's leaking as it will temporarely seal it.
Propane is another trick but dangerous if you're not careful, so I'm not going to get into that here.
It's a long shot but worth a try before you go taking a bunch of crap apart again.
Did you connect the hoses on the back of the intake?
Also, did you properly torque down the intake bolts? They require very light torque (100 in/lbs I believe) and if they're over tight it could cause distortion, thus letting in air.
You can also try spraying really soapy water (I use dishsoap) around the intake and TB anywhere there is a mating surface. It should foam up nicely but if there is a vacuum leak the bubbles will collapse. The idle will probably surge a bit too if you spray the spot that's leaking as it will temporarely seal it.
Propane is another trick but dangerous if you're not careful, so I'm not going to get into that here.
Why not try the old tried and true method of spraying choke/carb cleaner around the base of all areas of the possible leak? You should get an increase of rpm when you hit the spot, might just work.
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From: The Confederacy
Ok, here is what all I did to the car last night.
1. Changed out the TR6's with 2,000 miles on them to a new set, also installed my stock plug wires
2. Did a compression check while they were all out, every cylinder was right at 180psi.
3. Pulled vavle covers and inspected springs, check rocker bolts etc.
4. Re-torqued intake and checked vacuum fittings at rear of intake.
5. Pulled map sensor out of intake, checked grommet on it, reinstalled.
6. Swapped TPS from my stock TB onto the ported one.
7. Installed Two new O2 sensors.
After all that work and time the SOB is still doing the same thing on the way to work today. I'm almost positive it is in the tune now, it SCREAMS at WOT and runs great when you are normally accelerating, it is just the cruise and "tip in" that is screwed. I'm going to try to get in touch with Jason at TSP today and see if he'll look at the PCM for me.
I'm going to grab a can of carb cleaner at lunch today if I have a chance and try that too.
Thanks for all the input guys!
1. Changed out the TR6's with 2,000 miles on them to a new set, also installed my stock plug wires
2. Did a compression check while they were all out, every cylinder was right at 180psi.
3. Pulled vavle covers and inspected springs, check rocker bolts etc.
4. Re-torqued intake and checked vacuum fittings at rear of intake.
5. Pulled map sensor out of intake, checked grommet on it, reinstalled.
6. Swapped TPS from my stock TB onto the ported one.
7. Installed Two new O2 sensors.
After all that work and time the SOB is still doing the same thing on the way to work today. I'm almost positive it is in the tune now, it SCREAMS at WOT and runs great when you are normally accelerating, it is just the cruise and "tip in" that is screwed. I'm going to try to get in touch with Jason at TSP today and see if he'll look at the PCM for me.
I'm going to grab a can of carb cleaner at lunch today if I have a chance and try that too.
Thanks for all the input guys!
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TECH Enthusiast
Joined: Jul 2002
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From: Austin, TX
i think a lot of people cars do that...
mine does...
there are no misfires...at around 35 in 4th gear it will start to hesitate and buck...its just tuning. i just cruise around in 3rd in going under 40 and i dont have a problem...
i need another tune though...
mine does...
there are no misfires...at around 35 in 4th gear it will start to hesitate and buck...its just tuning. i just cruise around in 3rd in going under 40 and i dont have a problem...
i need another tune though...
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Joined: Mar 2003
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From: La Porte, TX
Originally Posted by mikemodano9c
i think a lot of people cars do that...
mine does...
there are no misfires...at around 35 in 4th gear it will start to hesitate and buck...its just tuning. i just cruise around in 3rd in going under 40 and i dont have a problem...
i need another tune though...
mine does...
there are no misfires...at around 35 in 4th gear it will start to hesitate and buck...its just tuning. i just cruise around in 3rd in going under 40 and i dont have a problem...
i need another tune though...
Same problem here, same solution. I'm just going to have the tables adjusted so that the car will not shift into 4th until 40mph. I'll also be switching out to a 3.73 rear, wich should bring the RPM's up enough at cruising speeds to fix the problem. It's just the big *** cams that we are running!
