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rpm drops

P

PhunnyJesta

New member
2002 GTP
72k miles
93 octane
list of mods in vbgarage

I made a post awhile back about noises from the s/c and some other problems but the s/c is just fine but im still having issues. Im getting around 500-1000 rpm drops when coasting in drive or idling in park. It never drops when accelerating or when its in neutral (idling or coasting). When the rpms drop it will shoot back up to normal and drop down again right away almost in a "beat" until i shift into neutral or shift down a gear.

Here's things I have done so far
changed oil
new fuel filter
o2 sim (since I had the high flow cat)
fuel pressure checked (50psi key turned over, 45 idle)

now I am not too sure about what the fuel pressure should be at, I think if I remember correctly idle should be around 45 but i have no idea about or if it even matters with the key turned over.

Also, with the o2 sim installed it got rid of 2 codes. The p0420 and i can't remeber what the number was but the computer was reading lean from the o2 sensor. I can always just plug that back in and fine the codes it was throwing.

Everyone seems to think its a fueling and telling me to get an adjustable fuel pressure regulator but I read an article on ZZP how it can mess with your tuning and offer nothing more then the stock one. How likely is a fuel pressure regulator to go bad though?


*EDIT*

also since im running a 3.4 pulley shouldn't I be running around 11-12 psi? It goes at the very max 10 and at idle its at 18ish vacuum
 
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10 psi on a 3.4 sounds about right considering stock psi is between 5-8 and .1 pulley drop gives you about 1 psi...You should see more boost when its cooler outside.
 
someone from my work just gave me an idea, could it be from too high of a heat range spark plug? I got that heat range with the intent of modding it up to need that but it looks like I won't be needing it any time soon, gonna be getting a lower heat range to see if that works
 
It's probably doing that BECAUSE of the o2 simulator. The '01+ cars NEED a rear o2. Toss yours back in and see if that fixes the issue...you will have to deal with the codes too...but if you have access to a tuner, just have them set to no report.
 
bluegtp91 said:
It's probably doing that BECAUSE of the o2 simulator. The '01+ cars NEED a rear o2. Toss yours back in and see if that fixes the issue...you will have to deal with the codes too...but if you have access to a tuner, just have them set to no report.
Click to expand...

Nope, nope, and uh nope.

You cant delete the codes... it will still run the cat test 3 times per drive cycle.

The ONLY issue from running no 02 is the fact that you will get a fuel dump under specific cruise only situations.

Under no situation is a o2 sensor going to cause issues like described.

For the OP.... The issue sounds spark related... but you are being fairly vauge for a diagnosis on spark stuff.
 
darkhorizon said:
Nope, nope, and uh nope.

You cant delete the codes... it will still run the cat test 3 times per drive cycle.

The ONLY issue from running no 02 is the fact that you will get a fuel dump under specific cruise only situations.

Under no situation is a o2 sensor going to cause issues like described.

For the OP.... The issue sounds spark related... but you are being fairly vauge for a diagnosis on spark stuff.
Click to expand...

The rpm drops still occured when I had the o2 sensor in, I thought the drops might have been related to the codes being thrown but it didnt help at all

I have TR6s on now and I think it might too high of heat range for my build, I was gonna go out and get some T55s tonight to see if that helps any
 


PhunnyJesta said:
The rpm drops still occured when I had the o2 sensor in, I thought the drops might have been related to the codes being thrown but it didnt help at all

I have TR6s on now and I think it might too high of heat range for my build, I was gonna go out and get some T55s tonight to see if that helps any
Click to expand...

Try regapping the ones you have in there to like .060
 
Also...if he is missing...why would be pull the gap OUT more. I'd close it...to .050" that way he has LESS chance of a misfire under load. Also...to hell with NGK's...TR6's are a cold plug...get some AL104's...gap them at .050" to start...if it cures your issue then there you go. Are your wires any good? When was the last time they were replaced? How do your coil terminals look? You can sand them down with some 2000 grit and put some dielectric grease on them to rule that out as well...auto parts stores test ICM's for free too...when your cleaning the coils...see if thats on its way out as well.

darkhorizon said:
Nope, nope, and uh nope.

You cant delete the codes... it will still run the cat test 3 times per drive cycle.

The ONLY issue from running no 02 is the fact that you will get a fuel dump under specific cruise only situations.

Under no situation is a o2 sensor going to cause issues like described.

For the OP.... The issue sounds spark related... but you are being fairly vauge for a diagnosis on spark stuff.
Click to expand...

Only giving my 2 cents because I experienced the same thing and it was a over fueling and flooding out issue...the rear o2 going back in from running a sim, fixed it. I did nothing else.
 
It is possible that the o2 fuel dump is causing issues... but not directly from it..

The plug gap increase will reduce fowling, and decrease idle/no load misfires.... Remember the only time this is an issue is during decel and idle.
 
I found TR6's and 104's burned roughly the same.

Also they're both too cold for my car.

Since I cannot find your mod list, do you have an overkill PCM?

If so, what revision? 4.0/4.1?

I believe they both had surging issues related to timing tables.

4.2+ has corrected this.
 
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under my name in each post is "my garage" but here is the list anyway

2.5 inch stainless steel exhaust pipe from CAT
2 flowmaster original 40 series mufflers
K&N cold air intake
Speed Daddy headers
Thunderbolt high flow cat w/ o2 sim
Intense Tuned PCM
TR6 spark plugs
180 TSTAT
3.4 modular pulley system
Ported S/C


gah looks like one of the spark plug wires got too close to the headers and bottom of it is singed but looks like it just discolored it a little. ill regap and get new wires but im gonna just regap the plugs first just for the sake of knowing if it was the cause or not
 


i found what I believe is a missing vacuum line, which ive looked all over but I couldn't find any loose line or anywhere it should go to. There is no pressure or vacuum coming from line as well.

its to the left of the tstat housing and has a vacuum line right underneath it


eUbvq.jpg



regapping the plugs today but letting the engine cool off a bit before i climb onto the engine to get the ones in the back
 
Re: rpm drops *updated*

*update*

The spark plugs and wires seemed to fix it for about week and started getting really bad rpm drops again and code p0171 was thrown. I had an intake smoke test done and I had a crack in the lower intake gasket (not sure why ignition fixes seemed to help fix a vac leak) and got that fixed and code is gone now except a new one popped up p0134 and now im getting ****ty mpgs (13-15mpg) and still having rpm drops. I put on a new o2 sensor and the code is gone for now but still have ****ty mpgs and rpm drops.
 


No i just had the garage that did the test fix it

the plugs themselves werent bad at all, the one wire got a little close to the header though.....
 
ok i fixed it, all it needed was a computer reset. Disconnected the battery for a few minutes and I am now getting back up to 20-22mpgs and no rpm drops
 
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