Weird idle characteristics in my Ttype......and more

[8UWITH6]

Hi guys. The last month or so I have been noticing that my Ttype is "acting up" so to speak. Just FYI, its pretty much stock with the exception of a fuel system, blue tops, 2 3/4" DP, K&N, free mods, Thrasher 92 (dont like it, but its all I got right now). It has 118K miles and is in fairly decent tune. Original timing chain, and valve springs though.

Heres the description of the "problem":

The car usually has decent vac at idle....15-17ish. And when in gear it used to be 12-13. The last few weeks or so, I have noticed that when I put the car in gear, the vac goes to 10, then drops down to 5 or so and the car is struggling to stay running. I usually tap the gas pedal to keep the vac up, even though the car has never stalled out on me. So coming up to a stop light, the car is almost stopped, and it does the same, BUT not all the time??? Sometimes when stopped at a light in gear, the vac will be 10, sometimes 12-13??? Its odd. FYI, tps is .42, LV8 is 30-40, IAC is 10-20, and of course BLMs and INT are 128 at idle because of the thrasher. Oh yeah, car runs great at WOT....18psi in 1st and 2nd gear, drops to 16psi in 3rd because of the chip. Highest EGT reading I saw in 3rd gear was 1589*, BUT GET THIS, my spark plugs are always WHITE when I change them???????

So I swapped chips today. I put the Jay Carter 93 from my GN in the T-type. And now it just plain doesnt want to idle worth a crap. Vac is like 8-10, and I gotta rev it every now and then. But with the JC chip, I can look at BLMs now, and they are 141+ at idle, in gear or not in gear. I tried adding more fuel, but it didnt help. So its lean as hell at idle, and even driving around town???? But why is it noticable better with the Thrasher? Because of the open loop idle? Should I reset the IAC/tps again? I need to just quit being cheap and geta good chip burned for my car, but for now this Thrasher has to do......I guess.

I know this is a lot of blabbering, but Id really like to know why my car would "struggle" to idle, with relatively low vac, but still have good IAC and LV8 numbers. Ive seen the IAC as low as 04 at idle, in park. Ive seen the LV8 as low as 30, and Ive heard 35-40 is a good number. There is no tip in stumbles, no coughing, no sputtering at all. It just doesnt like being put into gear, or coming up to stop lights???????? I appreciate anyone who takes the time to read this........please let me know what you guys think. As always, THANK YOU

 

[blackbuick87]

Try a compression test. Worn rings could cause these symptons and let it run good at WOT. With over 115k anything is possible.

I dont think the problem is the chip. I think the open loop characteristics of the Thrasher is masking your problem when that chip is in. You probably already know by now to check the MAF. Too bad you dont have a Translator or you could richen the idle with that

 

[scottyb]

Umm, I hate to sound silly, but how about a vac leak?

 

[8UWITH6]

2 days later, the car is doing better? 12 vac at idle in gear, and no trying to stall out. BLMs are still LEAN as hell though? I added a few pounds of fuel, I think its 43 line ON right now, was 40. Of course this is according to my fuel pressure gauge. I dont know, Im gonna be putting the Thrasher back in......maybe I should find a KNOWN accurate fuel pressure gauge? Any other ideas?

Scottyb, Im pretty sure there isnt a vac leak. I replaced every vac hose I could with the exception of the small plastic hardlines. Im thinking about doing some more in depth searching for leaks with soap water though.

blackbuick87, Im pretty sure the MAF is okay......however, at idle (with the BLMs pegged) the MAF shows 04. Im assuming that this is the computer trying to pull out as much air as possible to richen the car up?

Thanks for the replys, can someone please chime in here? THANK YOU!

 

[TurboJim]

What about a wrong PCV?

 

[blackbuick87]

4-6 is normal for the MAF at idle, all that measures is how much air in grams/sec the engine is pulling in. It is not adjustable. I think your FP may be too high. What is it with the line off? too much FP will only mask the problem, and you could end up washing down the rings with too much fuel. 43 Line on could be as high as 50 line off.

Try resetting your ECM to clear out those BLM numbers. Try adjusting the IAC up. Get it into the 30-40 range in Park and see if that helps.

 

[8UWITH6]

Jim, the PCV is the brass check valve type. I run this in my GN also, and have no problems in that car.

blackbuick87, I know that 4-7 on the MAF is normal. But like I said, its usually 6 or 7. Also, from what I understand, if your car is lean, the computer will knock the air grams down on the MAF to compensate? Maybe not now that I really think about it. Anyway, If I had too MUCH fuel pressure, then why are my BLMs pegged at 140+ showing me that its lean at idle? The higher the number over 128, the leaner it is, the more fuel the computer is adding to compensate? Right? Plus, Im pretty sure Im not washing down the cylinders because there is no gas smell in the oil, and the car is not blowing ANY smoke at all. The IAC seems okay, its probably 15-20 most of the time. And I have heard that that is optimum. Ill check the fuel pressure line off later tonight. It should be around 50psi (according to my gauge), but the BLMs should be between 120-136 or so just like my GN. I usually run it at 43-44 line off with chips besides the Thrasher on the bluetops. When the thrasher was in, it was 45 line off. Thanks for the replys..........

 

[TurboDave]

Odly enough, and this doesn't happen 100% of the time, the Thrashers and check valves DO NOT play well together.
You'll get all kinds of wierd symptoms, including inconsistent vacuum readings (doesn't have to be a thrasher for that).
You'll notice wierd BLM numbers at idle, strage vacuum signals, etc.

Get the PROPER PCV valve in there and most of your wierd problems will very likely go away.

 

[8UWITH6]

Sounds like your onto something Dave. I noticed different vac readings (lower and higher sometimes), when I changed the PCV for the check valve. So you think I should toss the check valve? Seriously, I have about 5 good AC Delco PCV valves laying around. I dont know, Ive heard that the check valve helps keep boost out of the crankcase. What are your thoughts on that?

Oh yeah, FYI, today driving home I had 15 inches of vac at a stoplight, in gear! The only thing that is still off is my BLMs at idle. 150s-160s, Jay Carter chip. I plan on getting a chip besides the Thrasher soon, but I have other things that I need to buy first. IE-tranny for the GN, grrrrrrrrrrr. Now where is that Jim Testa Chip for bluetops......................