jim86

iTrader: (1)

I searched the forum and came across alot of info on the dreaded surging idle, i put a scanner on it and was hoping some info could narrow it down before i start buying parts. I have checked fuel pressure (36 PSI at idle, stayed there awhile after shutdown), pulled 3 plugs which are black, not wet but it's definately running rich. Some background info, car is a 91 Firebird 350 TPI bone stock except i just put hooker 2055's, a maganflow cat and a hooker catback on, converting the dual cat to single high flow. The 02 sensor is new (bosch). Drove the car for a couple days it was running fine, then started surging at a stoplight and has been running poorly since. It does seem to run ok when accelerating or on the highway. With the scanner on it seems to run/idle ok in open loop with a BLM ranging from 118-128. When the car goes closed loop BLM immediately drops to 108 and the surging begins, with plenty of smoke out the tailpipes. There are no SES codes, some info below from the scanner in park. Any help appreciated.

BLM - 108
BLM CELL - 4
Coolant - 168
EGR Duty% - 0
Engine RPM - 800
Exhaust 02 - RICH
IAC Position - 75
IDLE REQ RPM - 738
INJ PW(ms) - 1.2
Integrator - 83
Loop Status - CLSD
Map(V) - 1.59
MAT - 113
O2S(mv) - 764
O2S Crosscnts - 57
Spark Advance - 15
Throttle(%) - 0
TPS Sensor(v) - .57

Viprklr

iTrader: (5)

https://www.thirdgen.org/forums/diy-...-blm-cell.html

Some useful info.

jim86

iTrader: (1)

Collected some data driving down the road today, as soon as i took off the BLM went to 128 and the cell moved around as well, only now the missing seemed to also be occurring driving down the road as well as idle. I'm starting to think it's ignition related, put the timing light on a few wires and the spark seemed erratic. I'm thinking this may be causing the rich condition. Any other thoughts?

jim86

iTrader: (1)

Took the cap and rotor off to inspect them (even though they are almost new, coil is new as well). Looked ok, nothing strange. Noticed when the car was idling the surging was very rythmic between 500-700 rpm in gear. Sprayed some cleaner in the IAC passage, no difference. Checked vacuum, pulled 18.5 inches at idle and stayed steady. Would IAC valve also cause problem at light throttle? Can ignition module cause problems like this, i thought they just "go" and it won't run.

jim86

iTrader: (1)

Went to check the timing tonite, when i grabbed the top of the distributor to rotate it i got a shock, tried again a minute later and it happened again on the other side. Even though these are new MSD cut to fit wires i think i'm gonna have to swap them out. They must be leaking somewhere.

afremont

Your story sounds allot like mine. Mine finally made it to the stage of right out shutting off while driving. At first it would surge and miss when warm, BLM of 108, etc... After letting it cool off, it runs fine again. I'm putting a new distributor in tomorrow.

You said you had some black plugs, so you may have some leaky injectors on those cylinders.

jim86

iTrader: (1)

i'm hoping maybe the wire are bad. Else i'm going the same route and get another distributor. As far as injectors, i put the fuel pressure guage on and it held pressure for awhile after i shut it off, so i'm hoping that's not the case.

JulieGTA

I have heard of new cap and rotors going bad right away.

This sounds like what happened when 2 of my injectors shorted out. They were stuck open.
The stock ones are known to go bad.
You would want to test the ohms of each injector. I'm trying to search for a link to it...

jim86

iTrader: (1)

Put some new wires on today, same thing. Runs ok when cold, after is starts to warm up it starts surging between 400-600 RPM in gear, 600-800 in park, sometimes like it's going to die if in drive. It also surges at light throttle, but not at WOT. I guess the next thing is to ohm check the injectors, they look original and have well over 100,000 miles on them.

afremont

Exactly the same story on this end. I put in a new module (followed by replacing the whole dist), plugs, wires, cap, rotor. Car would run fine cold, start missing hard in one cylinder when it got warm, followed by not being able to be revved under load, culminating in the car just suddenly shutting off and not restarting for hours.

Last night I found that when it was hot enough to not start that unplugging injector #5 would let it fire right up. #5 measured 6.0 Ohms when the engine is cold, the rest measured good. It idled fine if you don't mind only 7 cylinders. I plugged the injector back in and the engine immediately died.

THEORY: I explain the running good when you stomp the pedal on the spraying injector cooling itself better when it sprays fuel harder, or having wider pulse widths (more dwell). This would allow my car to smooth out when revving, yet return to a solid miss at idle. The injector never stopped clicking inside (stethoscope), but it's obviously sticking or not opening far enough or as fast as it should. The wider pulse widths of stomping on it seem to allow it to sorta work, but the narrow width of idle pulses aparently flowed little to no fuel on mine. It's looking like my injector shorts out shutting down the ECM drivers. The confusing thing about this problem is that it acts just like an ignition problem, but it's actually a fuel problem. The key thing I learned is to determine which it really is next time before spending money.

jim86

iTrader: (1)

Well, to follow that up, i just done Ohm checking the injectors. With the DVOM set at 200, i got the readings below. Looks like #2 is bad, but i'm still not sure why the ECM is seeing a "rich" condition?

#1 - 17.4
#2 - 2.6
#3 - 17.5
#4 - 17.4
#5 - 17.2
#6 - 17.5
#7 - 17.4
#8 - 17.4


I also unplugged that injector and started it up. It idled ok, even when warmed up. You could tell it wasn't running perfect but there was no surging whether in park or drive. Within 10-15 seconds of plugging the #2 injector back in (while running) the surging reappeared. I repeated this twice with the same results.

jbta99

If the injectors are stockers, don't waste your time, replace them all with Bosch III's. Just did mine yesterday. Engine runs smooooth cold to hot, acceleration is very smooth. Very happy.

jjlabinski

The 36 PSI scares me,

I have a new set of accel 24's I will let go cheap. I put ford 30's in mine.

Call me if your interested 216-226-6734

Jeff

afremont

Why so, 36psi is where it should be with high manifold vacuum. It should go to 42ish when stomped or first primed.

jjlabinski

You run that thing lean and you will find out why!

jim86

iTrader: (1)

It did go higher when given some throttle. When i had the scanner on it my problem was a rich condition, hence the 108 BLM. I'd still like for someone to give some info on how one bad injector can make the ECM think there's a rich condition. Since the FP holds when the car is turned off it doesn't appear it's stuck open.

afremont

I have a theory on that. I believe the injector is putting in "some" fuel at idle, but the mixture is so lean that the spark doesn't ignite it. The unburnt fuel is then dumped into the exhaust manifold where the 02 sensor sees it as a rich condition. In my case the 02 sensor is on the driver's side and the bad injector is also on that same side. Your case doesn't seem to fit my theory.

jim86

iTrader: (1)

I'm going to get a set of Bosch III's from FIC, and since i'll have it down that far throw on a new FPR and EGR.

PAformula

iTrader: (1)

I need to test my injectors also as my formula is doing the same thing. If anyone could provide the exact procedure for ohm checkin injectors, it would help me greatly.
Thanks

jim86

iTrader: (1)

Get a digital volt meter, set it to 200 ohms. Take off the connectors from each injector, one at a time may be best. You can do that by pushing the little metal clip in and pull up on the connector at the same time. Once off you'll see to pin type things sticking up where the connector went, put one lead from the volt meter on each one and record the reading.

JulieGTA

Thanks, jim86. I couldn't find a more straightforward thread describing how to check ohms.

I don't REALLY know what was going on with the injectors when they went bad, but they ACTED like they were stuck open. You'd think they would be lean but no.
There is probably somebody who knows exactly what is going on in there.

I have Ford SVO 24 lbs in it now.

Edit:
OK this is clear too, sometimes the search engine is tricky and can't come up with relevant answers.

https://www.thirdgen.org/forums/tpi/...-injector.html

jim86

iTrader: (1)

Well, got the injectors in, along with a Holley AFPR and new EGR. Car seems to running good but i still have a slight surge (about 100 RPMS) in park or drive and a pretty good off idle stumble. Not nearly as bas as before though. FP is set to 42 PSI when running, timing is 6 degrees BTC ... Probably look at the IAC next.

PAformula

iTrader: (1)

Is your coil original? If so, have it checked. Mine was bad, and quit altogether after swapping my injectors. If there is an Advance Auto parts near u i think they can check it for free.

mnorton

Be advised... I bought a Holley AFPR and tore 3 diaphragms before giving up and replacing it with a Crane AFPR. If you tear the diaphram it will leak fuel out of the vacuum port.

afremont

What is your IAC count once the engine is good and warm? Should be 40ish, if it's allot lower you have a vacuum leak somewhere. Make sure that AFPR is not leaking thru the vacuum port. Try cranking the pressure back to 35ish running and vacuum line connected, maybe you have it a tad rich. How's the exhaust smell?

jim86

iTrader: (1)

IAC count when warmed up is 44, seems in the ballpark. Car idles pretty good but when you give it very light throttle it runs rough, in fact if you give it just light throttle and let off it may die, but it will fire right back up. At about 1300-1400 RPM and above it seems to run fine. And it's pulling 19 in. of vacuum at idle in park.

afremont

Yeah, that sounds good. The higher the count the less likely it's getting air from somewhere else. Sure sounds like it's lean by the behavior though. Does your TPS value increment smoothly from idle? Only other thing that comes to mind is the EGR staying closed when it should. Does your BLM look reasonable.? After the injector install, mine went up to 133-135 at idle.

jim86

iTrader: (1)

TPS increments smoothly doesn't appear to stick, goes from .54 to 4.29 floored. BLM looked ok, 128 at idle, sometimes 120. I attempted to set minimum idle air for the IAC and ran into a problem. I followed the instructions in the tech article, jumpered A/B on the ALDL, waited about a minute, put my hand on IAC while waiting and felt a little vibration but didn't hear any kind of clicking. Pulled the paper clip out of the ALDL and started it up, but even when the screw was adjusted all the way back, i couldn't get the car to idle at less than 1200 RPM. All this while the EST was disconnected. Would that indicate a bad IAC??

afremont

I'm not sure that the speed density systems use those rules. For example our TPS isn't adjustable (just needs to be below 1V at idle position) and the IAC takes care of itself via the way the software in the ECM works. I think the way we set the IAC (never messed with mine) is by turning the key on and off a couple of times. I can't recall the exact procedure, I need to get my manual out and look.

G-4ce

iTrader: (1)

i recently bought a 1991 rs 305 tbi and replaced everything! cap, roter, plugs all accel and the iac, o2 sensor, cleaned the stock tbi out egr vacuum lines were replaced and then after replaceing the o2 sensor i started to get the surging sound everyones talking about and it was idleing high but ran ok not really missing but slugish and once i replaced the tps it fine now hope it helps

EastCoastHD

Per my 1990 C4 FSM :

a. Depress accelerator pedal slightly.
b. Start and run engine for 5 seconds.
c. Turn ignition "off' for ten seconds.
d. Restart engine and check for proper idle.

jim86

iTrader: (1)

Put in a new IAC, still the same thing. It idles ok, but just off idle it run very rough and seems to want to die. Give it more throttle it and runs fine. Going down the road or highway it runs good.

jim86

iTrader: (1)

Double-checked the timing, and it looked ok (8 degrees BTDC) but i noticed when i plugged the EST back in and i tried the timing light it very sporadic. I unplugged the EST and the light was steady. I didn't expect the timing to be accurate with the EST plugged in but i figured the light should blink just as steady, repeated this several times with the same result. Not sure what to make of it but it doesn't seem right, maybe a coil or ICM? Not sure why that would make it run poorly just off idle but OK at higher RPM's?

jim86

iTrader: (1)

Well i think i finally got a clue today. After driving the car around the other day, i checked it with a scan tool when i got home and pulled a code 32(EGR). The EGR valve itself is new, so i first checked the vacuum from the throttle body port. At idle it was 0 in. but went up to almost 20 as the throttle was opened, but also there was no more hesitation or stumble. It idled smooth and was also smooth when the throttle was opened. I'm going to check for vacuum leaks in the EGR setup but i think it's more likely the EGR solenoid. Anyone else have any info?

jim86

iTrader: (1)

Well, i redid my vacuum lines to the EGR valve and throttle body. Also took plenum off and removed valve, tested it via a vacuum line on my truck and it opened and closed as it should. Put it back together and still had the same stumbling off idle as before. Since i wasn't sure if the EGR solenoid was good i had it out of it's mount where i can do some things with it. If i removed from the solenoid the hose that went to the throttle body it accelerated smoothly, as soon as i put it back on it stumbled off idle. I guess i'll be looking for a new solenoid unless there's some other reason that could be occurring??

goonerstint

I am exactly where this left off except I have already replaced the solenoid and is still only drivable with the vacuum line to the EGR pulled and plugged wont run great only drivable.

jim86

iTrader: (1)

Turned out my problem was a bad injector, found that out doing an OHM check one by one.