...Here is the down low: '87 Iroc 350 TPI, 700r4, 100k, new jasper with <1000 miles on it, Flowtech ceramic coated headers, K+N's, air-foil, and all of the free mods.
...Here are the symptons: there is a slight stumble at idle(I couldn't even set my IAC because the car wouldn't idle at the specified 400 RPM with it disconnected), lack of power through entire RPM range, about 3/4 efficency on fuel consumption, no trouble codes other than 12, and my auto x-ray says it is consistantly running lean. When the car first starts, open loop I assume, it has better than normal off idle power, so I decided to just dissconnect the o2 and see how she'd run. The off idle power was still better but thats about all, and there weren't any noticable fuel consumption gains or losses. My o2 sensor is at the top of my suspect list, because it isn't a heated unit and also because I had to lenghten the lead to get it to work with the flowtech's(was that a stupid move?). My scanner reads varring between 300 and 420 mV at idle, does this sound in range for the o2? My fuel pump seems to be suspect also, because lean means not enough fuel and because I tried the preasure relief procedure( pull FP fuse and let engine starve to a stop) the other day and it didn't work. The idle was terribly choppy and the engine never actually stopped.
Please help me with any scanner suggenstions or anything else to check, I am running out of options and the local mudstains are starting to catch on!
Thanks a bunch-
dan

 

Yep, the O2 sensor is the issue if you're reading 300 and 400mV at idle. Normal readings should be cycling from 100-900mV. Either that or there is an issue in the car that is making you really run lean.

 

My 87 305 TPI, would idle like crap until I programmed my own chip to idle at 600. The 550 was too low and it would try to stall.

Chek the temp reading from the computer, If it is off, it could throw everything into a frinzy.

Just a thought

------------------
87 Formula Yellow/Black
Engine & Transmission
.040 over 5.0 converted to TPI, 9.5:1 Compression, SLP Cam Dur 206/212, Lift 480/487, Cent Line 112, SLP headers, SLP cat-back exhaust, K&N Airfilter, Modified Stock cold air intake, Ported & polished Stock TPI intake, Holley Adjustable Fuel Press regulator, AC Rapidfire Spark Plugs.
Gil Younger (no yo-yo) Shift Kit, Aluminum Driveshaft, 3.73 Posi gear
Suspension & Brakes:
Baer 12" brakes 4 wheels, KYB AGX Adjustable Shocks & struts, Hotchkis strut tower brace, South side machine frame connectors, Custom reinforced control arms and pan hard bar.
Interior:
Custom Leather interior, CUSTOM Yellow Gauge Faces, Kenwood Receiver, Pioneer Speakers, Kicker Substations, Kenwood 10 Disk Changer, Pioneer Amp.

87 Formula TPI (5 Speed) Yellow/Gray STOCK

1967 Buick Riviera 430hp Turns high 14's (Not bad for 4300 lbs)

83 Camaro (Parts)
83 T/A (parts)

http://www.3rdgenformula.com

 

Well, I did some more looking around. Coolent temp sensor checks out ok, it is almost brand new. A vac. gauge brings up about 17 or 18 inches at idle, which seems about right. Here is the kicker, I installed a fuel gauge, and at idle it is running 35 psi. Isn't the stock setting 42.5 psi? When I give it some throttle, the presure shoots up noticably, so that seems to rule out the fuel pump, right? Now signs seem to be pointing to my fpr and I have an afpr sitting around that I was going to install after I got all of the bugs worked out but mabey now is the time to do it. Do these keep the fuel pressure at one value or is it dependant apon engine load?
thanks again guys

[This message has been edited by Remondino (edited July 02, 2001).]

[This message has been edited by Remondino (edited July 02, 2001).]

 

Your FP is vacuum referenced, there is nothing wrong with 35psi at idle. The 43 psi stock you mention is with no vacuum applied to the FP regulator.

I'm leaning towards the following problems, in any combination, in no particular order...
-a dirty/clogged injector on the DS bank. This will give you a very lean cylinder, skewing your O2 readings lean and making the rest of the engine run rich, also hurting your gas mileage. This could also account for your stumble.
-bad/misadjsted TPS. For the stumble problem
-let me guess, you have gutted your MAF screens, maybe even ported the heat sinks. Believe it or not, this also has been known to cause the problems you describe occasionally. Some people get away with it, some have fits. If you have modded your MAF, it IS suspect and CANNOT be ruled out unless you put a stock MAF on it and get the same problems. Period.
...ed

------------------
Ed Maher - Moderator @ The Carb Board
92 Z28 Convertible - Quasar blue / Tan top
LB9 4L60 GU2 G80 - stock, soon to be sleeper
-=ICON Motorsports=-

- Definitely prototypes, high powered mutants of some kind. Too weird to live, too cool to die

 

These all sound like good points to make. My MAF screens have been removed but the fins haven't been. My scan tool gives a steady 5 grams per second at idle from the MAF. My tps has just been adjusted to a stought .6 volts at idle. I did notice that it didn't reach the specified 4 volts at WOT though. The specs on this don't seem to be real picky so I let it slip, is this a possible canidate, my power problem isn't just at WOT remember. The three wire unit I bought to replace my O2 sensor is about to go in, we'll see what its effects are. Injectors are my next step and I am not sure how to address them. Still looking...

 

These all sound like good points to make. My MAF screens have been removed but the fins haven't been. My scan tool gives a steady 5 grams per second at idle from the MAF. My tps has just been adjusted to a stought .6 volts at idle. I did notice that it didn't reach the specified 4 volts at WOT though. The specs on this don't seem to be real picky so I let it slip, is this a possible canidate, my power problem isn't just at WOT remember. The three wire unit I bought to replace my O2 sensor is about to go in, we'll see what its effects are. Injectors are my next step and I am not sure how to address them. Still looking...

 

These all sound like good points to make. My MAF screens have been removed but the fins haven't been. My scan tool gives a steady 5 grams per second at idle from the MAF. My tps has just been adjusted to a stought .6 volts at idle. I did notice that it didn't reach the specified 4 volts at WOT though. The specs on this don't seem to be real picky so I let it slip, is this a possible canidate, my power problem isn't just at WOT remember. The three wire unit I bought to replace my O2 sensor is about to go in, we'll see what its effects are. Injectors are my next step and I am not sure how to address them. Still looking...

 

sorry about the multi-post, my browser rump-wrangled me.

 

No sweat, it happens, just remember that you only have to hit it once unless your browser crashes. If it is really taking forever, stop it, hit back and reload. Your post will prolly show up, but it was waiting for the reply from the server.

anyhow, for the injectors, check out http://www.cruzinperformance.com/fuelinj.html , this guy has been recomended/used for years by people from here. You can get yours cleaned/flowmatched for around $100 , and he has quick turn around.
As for the MAF, i believe you canput the screeens back if you have them. If not, well, worry about that after the injectors cuz that seems more likely for your lean O2, rich running condition...andthe O2 itself. The hesitation is more like the MAF.

..ed

 

I believe Ed is absolutely correct. I would beg, borrow or whatever a stock MAF and re- X-ray your car to review your lean/rich condition.

Then if that is your problem and you want to remove your screens you will know what you are dealing with at least.

Keep in mind though a stock MAF (with screens) can outflow a stock 48mm and a 52mm Throttle body, so gutting it is kinda' pointless.

 

i had a similar problem, turned out that my EGR was sticking open and causing exaust gas to be fed into the cylinders all the time. the MAF more than likely is not your problem. ive removed my screens with no problem. the heat sink is there for a purpose though so make sure that stays.

 

What was found to be the problem? I am sort of having the same on my TA

 

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