Ok guys, I have been working on this problem since I bought this car. When I bought this car it had been sitting for about 2 years. The car has roughly 106,000 miles on it. When I drove it home it had a very surgy idle, 450-1000rpm. The intake gasket blew not long after bringing it home, so I got the pleasure of my first TPI teardown. While fixing that I did the usual tune up; plugs,wires,cap,rotor,new K&N, as well as a new IAC, new Accel 24# injectors, new vacuum check valve(orig one broken), EGR valve temp switch(broken as well), new balancer(orig one was spun). After all that she is running good but the idles still surges, not near as bad as originally but surges between 450-800rpm. I have checked everywhere for vacuum leaks and have found none. I purchased WINALDL and ran a scan. I am unsure of what exactly everything means. These are the readings while sitting at an idle:

raw converted
IAC 76 76
Coolant Temp 162 178
EGR 0 0
RPM 41 1025
TPS 27 0.53
INT 103 103
O2 55 0.243
MAT 125 120.9
Oldpa3 130 130
BLM 108 108
Rich/Lean counter 185 185
MAF 2052 8.02
BPW 53 0.81


It also showed under the flag data tap that: DRP occured, it was in closed loop, there was a Rich flag, EECC Slow O2 Rich/lean flag, BLM enabled, EGR switch closed, no A/C request and a fan request.

Any help would be great. Thanks guys.

 

It could be the accel 24lb injectors.
I think the stocker's were 22lb, anyway your BLM's are saying its very rich (a number below 128-BLM is rich and above 128 is lean) and the different injectors are probably flowing more fuel than stock.

I see 3 possible solutions:
change to stock/stockish injectors,
put in an adjustable fuel pressure regulator and reduce pressure to match required fuel,
or have the ECM/prom reprogrammed to run the accel injectors.

if you've done any mod's or plan to do any (like change exhaust ect.) then the reprogramming could maximize power. you might even get some more power out of a stock motor.

oh, if you haven't changed O2 sensors yet you should start there, with 100k miles on her its time anyway and it might just be the whole problem....

 

I was wondering if it might be the O2 sensors, I have noticed a rich smelling exhaust. How much pressure would I need to be running if I put in an adjustable pressure regulator and left in the 24# injectors? I do have a cat back Borla exhaust on the car right now. Thanks for the tips.

 

The flow correction is roughly equal to the SQRT(P2/P1)

So considering 24# injectors vs. stock 22.9# and squaring both sides:

Flow correction = (22.9/24)^2 = P2/P1 = 0.91.

So you would want to set your fuel pressure to 91% of the current value.

Assuming 46 psi is your current pressure (typical for 88 and later cars):

46*0.91 = 41.86 psi.

Since your BLMs are very rich at 108, I would go a bit lower to start with, maybe start at 40 psi in this example.

Have you checked your fuel pressure? Is it in the correct range for your year of car or has it already been increased?

Normal ranges: 34-40 psi for 85, 37-43 psi for 86-87, 41-47 psi for 88 and up.

I just saw you have and 86. So if you're starting with 40 psi nominal, try dropping down to 36.

This is starting to remind me of RRT Vette's ongoing issues with his 86. Rich smelling exhaust, 108 blms, 24 lb Accells etc., etc., all sounds very familiar. Maybe Dusty will chime in.

Note: You may have problems trying to reduce the fuel pressure this low due to plenum interference with the adjusting bolt. Keep this in mind when buying an AFPR. Some designs may offer more adjustment range without interference, or you may need to use a shorted adjustment screw.

 

lowering the fuel pressure can be double edge sword, with less pressure you get less atomizing.
I would say 4psi drop in pressure should be enough (you'll need a gage to see what pressure its running now). I wouldn't go anymore than 5psi just to be safe.

do change the O2 first, then re-scan to see if there is any change.
O2 sensors usaully last about 70K miles (more or less) and you may be needing a new fuel pump before long (pretty easy job on the vette).

if your going to be doing your own maintainance a fuel pressure gage is a good tool to have.

 

From looking at those scan numbers I see the O2 signal at 0.243 at that moment which is lean and the BLM at 108 which indicates rich. If you don't know how many miles on the O2 sensor, go ahead and change it as it is a maintenance item. Also you should see the O2 sensor voltage jumping all around very quickly.

I have an 86 that was a project to start with 6 years ago and still is. It sat up for 4 years. I replaced the fuel pump and the intake manifold gasket. At the same time I install 24 lb Accels and later a AFPR and dropped the fuel pressure to 40 psi vac off and 34 psi vac on without change. The scans I ran showed a richer O2 signal and BLM's at 108. After about a year of off and on working on the rich exhaust smell, ect. I decided to recently go back to 22 lb stockers. I haven't ran a scan to see if anything has changed, but the exhaust smell had lessened some.

About the surging idle...does it surge in open loop or closed loop or both?
That sounds like a vacuum leak or from the O2 sensor voltage you posted...maybe unmetered air entering the exhaust stream creating more O2 and causing the ECM to dump more fuel than is needed.

I didn't notice, but does the SES light come on?

 

you also have to let the car "learn" the new iac, the service manual has new iac learn proceedure.

 

Hey guys, sorry I was away for a few days. Ok, the fuel pump was replaced about 31,000 miles ago, the car surges when it is in closed loop and not when in open loop. As far as I know the o2 sensor has never been replaced. The SES does not come on. There are no codes being thrown. I need to order new hub/bearing assemblies, so when I do I will order a new O2 sensor as well and see if that works. I definately need to get a fuel pressure gauge. I did check fuel pressure(borrowed from a friend) after I orginally got everything put back together and I remember getting about 38psi with vacuum. I know Tequillaboy said to drop it down to 36psi, will that 2 psi make that big of a difference? I really appreciate all the help and advice guys.

 

Just to clarify: The fuel pressures I mentioned should be without vacuum.

If you're getting 38 psi with vacuum, then the actual setting without vacuum will be something even greater (maybe 45 psi or so, depending upon how much vacuum the car pulls).

I would suggest reducing the fuel pressure without vacuum down to 36 psi as a starting point to compensate for the larger injectors.

This should have the effect of bringing the blms up in closed loop and will also generally lean-out open loop which is apparently too rich based upon the blms in closed loop.

When the BLMs are running near 128 you will have basically the same mixture in open and closed loop control which is desired. The open loop target AFR will be slighty richer, but they should be close for warm coolant temps. If the open loop calibration is close, there should be little compensation via BLMs required in closed loop.

For idle, I think the mixture issues must be addressed first, but here is another approach that may help also.

Some have had success improving idle stability, by reducing the IAC authority on the idle airflow.

This can be done by increasing the min air adjustment with the throttle stop very close to the warm target rpm and resetting the tps back to normal voltage (0.54volts).

When adjusted in this manner the IAC should run at very low counts in a warm idle, since the majority of the required air is supplied by the throttle. The IAC will not be able to reduce rpm much below the target rpm which may help improve stability.

Note: You may have some temporary high idle conditions with this approach especially upon closing throttle following heavy throttle acceleration, since the IAC follows the throttle position. The IAC combined with the increased throttle opening will provide more air than originally intended in some cases.

 

i changed out the O2 sensor and there was no change. she still surges just like before. it feels like she's running a little better but still surging. is an AFPR my best bet?

ol,RJ

if you've done any mod's or plan to do any (like change exhaust ect.) then the reprogramming could maximize power. you might even get some more power out of a stock motor.



do you have a place or a person you recommend for reprogramming the computer? I am all for unleashing more power.

I appreciate all the help guys

 

I always recommend finding someone close by that you can take the car to (cuts down on the time it takes and gets the best job done).
check with your local car nuts and or the "west coast" part of the forum, should be someone in CA. with a good rep.

BTW, since you are in CA you probably have emission's to worry about. that makes me think that changing back to stock injectors might be your cheapest solution (sell the accells to recoup $).
If you find a local shop to retune the ECM they may be able to insure you can pass the smog (with the accel injectors) so thats another reason for you to find someone local if possible.
RJ

 

i still have the stock injectors, so swapping out shouldn't be a problem. i can put the accels to use on my TPI motor i'm building for my firebird. I was originally told the stock injectors were 24#ers thats why I bought those. Lately i'm being told the actual stock ones are more like 22.9#. Does that 1# make that big of a difference? Yes I am plagued with smog emmisions laws here, it makes things interesting. Thanks for the help.

 

injectors can vary alot (they also vary by what fuel pressure they are designed to work at).

I tried switching from a 30lb down to 26lb injectors (with higher fuel pressure) thought it would be easy since they should both be flowing the same amount of fuel.... wrong.
I had to retune some areas because the finer atomization (higher pressure) burnt quicker. so I had to richen it up in some places to get back where I was before.
your's could possibly go the other way (big injector @ low pressure) and could have areas that were still too rich due to unburnt fuel/less atomization (and if it happened it would most likely be at idle).

all those things can be corrected with proper tuning/ecm reprogramming of course. but you could get your stock injectors cleaned/checked or replaced for less money.
and the stock injectors will work with a fare amount of future modifications, so there's no need to go bigger unless you change intakes or bolt on a blower.

 

Ok guys, here's an update. It a turn of unexpected events I have stumbled onto what seems to be the biggest culprit of my surging idle. On my way to an autocross event, My alternator went out. Upon changing it out with a new one, my surge has all but ceased. There is a very small surge(barely noticeable). The car runs better and I can finally hear it idle nice. I am still going to switch injectors back to stock and see if what little surge is left disappears completely. Thank you guys again for all the help and input.

 

Interesting ... thanks for posting the follow up.


Gary

 

No problem, Ill post the results after i change the injectors out as well for anyone else who is following this thread.

 

Undervoltage can certainly cause mixture problems.

The ecm compensates the injector pulse width as a function of voltage.

Last year when my alternator was failing, I actually burned a couple of chips in order to better tune the Injector PW vs. voltage function so I could make it to the auto parts store and on to home.

It helped my car considerably after some tuning of the PW correction for voltages between 12.8 and 9.6 volts.

 

Last year I took my wife's van in for emission testing and it failed. I thought that was odd because it was in good shape. A few days later the alternator died. After replacing the alternator I had the van re-tested and it passed.

Wow


Gary