joecool108

Hey guys, I have a 91 Vert that I purchased about 3 months ago. 140K miles. The car ran awesome when I first got it about 6 weeks ago it started running like crap. I originally got 20 MPG, now I am down to 16 MPG. Car runs very rough at idle when cold. Runs like it has a cam in it and runs very rich. Once it warms up it idels much better, but will sugre slightly about every 10 seconds when at a stoplight. One car is warm runs ok, but when I turn key off and then try to start again, it runs rough again, almost like the computer forgot what its supoosed to do. Im pulling my hair out trying to find this! Its been weeks...! Here is what I have changed: Cap,Rotor,plugs o2 sensor, map sensor, IAC motor,Coolant temp sensor and harness. EGR valve, fuel filter,fuel pump replay,PCV valve Vacuum line to MAP Sensor. It seems like an electrical problem. The wires are about 6 months old. Im not sure where to go with this! Any help is appreciated.

Thanks!

RFmaster

Have you checked fuel pressure??? How old is your fuel pump??

//RF

joecool108

i have no idea how old it is. Whats the best way to check the pressure? Engine at Temp or engine cold? if it is pressure then why does it run ok when warmed up? When I release the fuel cap there is alot of pressure in the system.

RFmaster

'cool108

Welcome to TGO

1) I am kinda scratching my head since you have changed a bit of parts. Well, to start take a look at spray pattern of your injectors at idle - spray cone should be hitting the TB side walls and misty. There should be no drips or streams of fuel at normal operating conditions (at idle).
2) If you have ALDL cable and lappy do a quick data log from cold to fully warm while engine is idling. ALDL data log will tell us what ECM sees while engine is operating. You may have FPR with a flaky spring causing fluctuation in fuel pressure.
3) TBI systems does not have a fuel pressure test port (Schrader valve) like TPI. Measuring FP on TBI is a bit more involved. You can rent a fuel pressure gauge from auto parts store which has TBI adapter - basically a T that screws into inlet port. Stock TBI system runs best at about 12 to 14 PSI.
4) Gas tank pressure build up could be due to couple things - but mostly CCP canister needs to be checked and it filter replaced.


//RF

killacamaro

iTrader: (5)

RF IS THE MASTER, LISTEN TO WAT HE SAYS

he got my car running!

joecool108

Ok Ill check the spray pattern.

I have a snap on scanner so Ill get the values of all the functions.

Question, if it was a fuel problem, why would it run much better at normal temp? I would think it would run like crap all the time..

Thanks for the advise ill try it and get back to you

HandOfDoom

I had this same exact problem a couple of weeks ago replaced so many things in the engine than found a broken vacuum line. My advice would be to check for vacumm leaks.

RFmaster

'cool108

Well thanks, but I am no miracle worker. I just try very hard.

Regarding why it runs better when it is fully warmed up. One simple explanation is that when engine is cold it requires a richer mixture - aka choke on the carburetor. In EFI, mixture is richened by increasing the length of time fuel injectors are delivering fuel. If fuel pressure is low, which could be the case - old tired FP, not enough fuel will delivered. For the first two or so minutes, after a cold start, ECM is delivering fuel in open loop - i.e. NBO feedback is not used. ECM relies on stored VE tables to deliver proper mixture, based only MAP, CTS, TPS, and engine RPM as inputs. If fuel pressure is low VE tables will not match actual fuel requirements of the engine.

After two minutes and once CTS reports normal operating temperature (about 50 to 60C and above) ECM will try to enter into close loop. By varying injector pulse width NBO cross counts are observed. An increased injector duty cycle is indicative of a low pressure at idle. Visually, lousy fuel spay out of injectors points toward low pressure. In close loop engine will be happy, but your BLM are way high 140+ that would mean that ECM is adding fuel, possibly due to low fuel pressure.

It is a good thing that you have a scanner - a data log that you can post would be better. Take a look at this post, it may give you additional hints what to look for. Luckily Max had ALDL cable and lappy, but scanner would also work.

https://www.thirdgen.org/forums/tbi/...extremely.html

//RF

golden

Sorry but pressure built in the gas tank is absolutely normal . That's why we have an EVAP canister , a purge solenoid and a vent solenoid .

Thank you

RFmaster

Thats what I said. But if CCP solenoid is not functioning or ECM harness is disconnected the purge system will not purge excess vapor pressure into TB. Another reason for pressure build up is when fuel pump circulates excessive amount of fuel through the system effectively warming gasoline up. I found this when 255 lb/h pumps are installed into otherwise stock TB system. These pumps are easily capable of delivering fuel in excess of 80 PSI when only about 30 PSI is really need. When gasoline temperature is increased in a sealed vessel, like a gas tank, the vapor pressure temperature drops allowing for vapor build. This is basic chemistry.

//RF

joecool108

ok here is the values ice cold:
Open loop
RPM 725
Integrator 128
tps voltage .52
O2 volt Varies
Block learn 128
IAC 151 and drops as warms up
AF Learned NoA Synch pulse no
coolant 22
MAT 27
Map V 2.84
Map Kva 65
ESC Counter 0
Knock no
Batt voltage 14.1
TCC command P1

Here are them warmd up
Closed loop
1050 RPM
O2 Varioes rich lean
Interhrator 105
TPS .54
Block learn 108
IAC 4
AF Learned yes
A synch pulse no
Coolant 89
MAT 56
MAP V 1.80
MAP Kpa 44
Bat 14.0
TCC command P1

Any ideas?

golden

RPM's too high when warmed up and it does indeed runs a little too rich ... Have you checked the coil fire with a spark tester ?

joecool108

RPMS are in park, not drive. Sorry forgot to mention that. Havent checked the coil, what is a spark tester? If coil was bad why would it even start or run?

RFmaster

Joe

From close loop data it appears that it runs way too rich! Both BLM & integrator are at their respective minimum ranges 105/108! ECM is taking out fuel.
Check all your plugs/wires. Check distributor and coil. You may have a weak spark causing a rich condition. Look for black, wet spark plugs which would indicate weak or no spark condition. External coils are prone to fail. Also check mounting -ground bolts on the coil - corrosion may reduce spark voltage.
Do you know if scanner is returning any codes??

//RF

joecool108

RF

Changed coil last night and still runs the same when cold. Plugs are new and wires are about 3 months old.Cap and rotor are about 2 weeks old. Ill pull a plug and see what they look like. It seems even when it is warm when i shut the car off and try to restart it doesnt want to idle, it runs rough. Its almost like computer is losing its memory. Fuel stream from injector is a spray and hits the side wall and there doesnt appear to be a drip.

This is driving me nuts!

RFmaster

Joecool108

Well, you got to keep your cool!.

First it does not appear that your ECM is loosing its mind - it is simply responding to inputs in a programmed fashion. Also, from your description it looks like injector fuel spray is correct. The question is why is it running so rich. There are couple of possibilities:

1) Higher than normal fuel pressure or a leaky injector. You should verify fuel pressure with FP gauge. Auto parts stores rent FP gauges. Leaky injector is a bit more problematic to resolve. One way is to swap out injectors with known good one. You may not have this luxury, but if you frequent JY's TBI injectors can be had for about $10 a pop (305 are very common). Send them to a injector service - for example WitchHunter or many others for cleaning and flow testing.
http://www.witchhunter.com/

2) In your laundry list of replaced parts you have listed new O2. You can force ECM to simulate a lean condition by disconnecting O2 lead and grounding it. After a while this will set Code 44 - O2 voltage is below 0.3 Volts. You should see a difference in engine operation.
When engine runs rich O2 voltage stays above 0.6 Volts and that will set Code 45. You can simulate rich condition by applying voltage to O2 input through DVM (set to measure Vdc) - per factory manual. If you can simulate lean condition by grounding NBO then your O2 was probably poisoned (unless FP is high or injector is leaking - see section 1). O2 can be poisoned by lead in the fuel. Ethylene Glycol can also affect O2 sensor performance. The other, but more sinister poison agent is all too common painters RTV - that stuff can kill O2 sensors left and right. Never leave open painters RTV tube inside closed garage. RTV poisoned O2 will force rich condition!

3) Finally your cat (and I did not mean your Tabby) could be all clogged up. After 142k it is likely as well.


Well let me know if this makes sense...

//RF

joecool108

RF,
Thanks for the advice. Here are a few more things.
1) Ill check FP this weekend when i got home tonight Scanner says code 32 EGR and 33 MAP both are codes in memory. EGR valve is new also as well as MAP sensor.
2) On the scanner I watch the O2 voltage go from very low to very high and watch the rich/lean/rich so I would think thats working ok? when the O2 voltage is.3V it doesnt run any different.
3) Whats NBO?
4) When I put the O2 sensor in (its a Bosch) it went from the box into the car, i got it right from the store and all i used was a small amount if antiseeze on the threads.
5) I thought CAT at first before I started chasing electrical gremlins, I disconnected it and seems to be hollowed out. I can look straight through it to the exhaust pipe. I also took the Y pipe down and there appears to be no clogs.
The frustrating this is it ran awesom for a month then one day did this stuff! My wife drives a 94 Burb with a 350ci TBI and it hasnt had a bit of problem for 200K! We have had it since new and Ive done all the maint on it. Still original O2 sensor and all others are OE. Only changed EGR valve on that motor.

Gladstoneiroc

iTrader: (1)

Anyone else see the high map sensor value when cold? I don't remember what original ecm used to show, but I would be willing to guess that it too high.

RFmaster

Hey Joe

1) Since you have codes stored - you should clear them by disconnecting negative battery terminal for about 1 minute or so. This will clear all stored DTC codes as well as stored BLM values. ECM will have to re-learn, but it will do it any way. There is a possibility that ECM is stuck in limp mode due to stored DTC. Your MAP is working - scanner is reporting reasonable MAP values at idle. EGR DTC is a little bit more involved (to be set). What does your SES light do during ignition key off to run sequence?

2) NBO stands for narrow band O2 sensor. Some had BOSCH fail straight out of the box. In my experience I run both BOSCH and DELCO in my cars - knock on wood both performed as advertised. Since your voltage is swinging (0.3 to 0.8 ) that would indicate functioning NBO - scratch poison idea.

3) Vacuum leaks - check TB to intake manifold gasket. These are known to leak with age. A leaky gasket will play havoc with fueling.

4) When you replaced IAC motor did you reset it?
https://www.thirdgen.org/tpimod2

5) Since 'tabby' is missing in action we'll skip this problem for now.

//RF

joecool108

well more troubles.. last night on the way home from work, alternator took a dump.. discharged the battery and AAA had to tow me home. Well A new alternator and a few hours to charge a low battery, car fired back up. I was hoping this would cure it, but it didnt.

1) Codes cleared and EGR code popped up again, SES light isnt on all the time, once the key is turned off code is stored. Dont think were stuck in limp home mode because when car is worm, it runs good. SES light is on with key on no start, but when cranks and starts it goes off.
2) If car is warm, and I shut ignition off and then try to restart it struggles to run at a normal smooth idle, it runs like it has a big cam in it. If i drive it for a bit it seems to go back to normal.
3) Vacuum leaks, all hoses and plastic lines have been changed so dont think I have an issue there, but didnt check TBI base gasket, i can tell you tbi is tight, i checked that thinking that could be an issue.
4) Didnt know I had to reset IAC, will do that this weekend.

rough

i concur with this statement

Uglybronco

iTrader: (2)

I tell ya what, just give me the '91 vert & I'll deal with the rough warm ups. I don't mind :-)

joecool108

i have had them all plugged off and still have the same problem. Ive even checked the steel line that goes to the brake booster (it was disconnected and plugged at the TBI base. I have replaced all lines except the one that goes to the heater valve. If it was a vacuum line, it should run rough all the time correct? Which line was broken on yours?

Damon

EGR valve sticking partially open?