joecool108

Hopefully someone can help..
My son has a 1991 Coupe 3.1L with Headers, problem started about 3 days ago... Problem is car runs smooth, but on occasion sputters, is sluggish. Best way to describe the problem is its running on 6 cylinders, but throught the RPM range it runs like you flipped a switch and cut electrical power to one or 2 cylinders. Then goes back to 6, back to cutting out. Almost like having a straight line for 1 foot then a spike up.. then back to normal. When you try to floor it, it has no power at all when its in the "sputtering mode" almost like trying to jam a radar signal.. Best way to describe it is there is moisture under the distributor cap and there is an intermittent cut out..

So last night, We checked the wires and found 1 terminal on the cap was coroded with white chalk type material when you pulled the wire, and the wire had corosion so we changed it.. The wire and cap. Drove it again.. ran smooth, but then about a mile into the drive, same problem.. brought it back, pulled plugs, they looked good, but we changed them.. drove it.. same problem,, came back.. changed ignition module.. drove it.. same problem...

Car is full with premium fuel 93 ocatane... When I plug my snap on scanner into the port.. no codes at all, car in closed loop.. o2 sensor working correctly. Fuel pump is about 6 months old... Tried Idle relearn.. nothing seems to work.....

Any ideas are appreciated.. HELP!

Cadaver_Puncher

Check the ignition control module. They have been known to act screwy when they get hot.

joecool108

I changed it and put a GM one in it. Same issue...

mcrandrz

Take out the iac valve and clean it. Then check your iat sensor on the air box. If neither of those help then i'm thinking fuel. Check pressure at the valve on the fuel rail. Spark will not cause this. I've gone through this problem last month.


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sixgun

One issue I found with my 1990 car was the TPS. It worked, but not very well.

Basically this item looks at the throttle position and tells the ECM that it may
add more fuel because the engine is being asked to go faster.

I had to actually watch the TPS output to catch this.

The tired one showed less than a volt at idle and only 1.5v at nearly 75% throttle.

The service manual talks about this sensor approaching the full 5 volts with
lots of throttle. So, mine worked enough that the ECM didn't set a code for it,
but not well enough to schedule fuel while driving it.

Joe

joecool108

OK Update from last night:
1) Changed Fuel Filter
2) Cleaned IAC
3) Replaced TPS

Car now runs, and only stumbles on occasion but has no power.. you can put the pedal to the floor and its not smooth all the way through the RPM range.. I drove it 30 miles to work today and got it up to 75 MPH, but car has no power.. I also checked the timing and it is 10 deg BTDC.

Whats next??

mcrandrz

Good. We got it running. Next. I got to the point your at now after my iac and iat. check your spark plugs. I had bosch 4 platinum which in our cars are terrible. I changed those and wires and I've been good.


Is she sputtering and hi rpms? Or just making the noise and not going anywhere?


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mcrandrz

Also. Is your tv cable adjusted correctly? That affects shift points and acceleration.


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joecool108

The car is a 5 speed, no TV cable
Ill need to swap the IAT, Maybe I can try tonight
Sputtering has been minimized, but car has no power.. I pulled the plugs and cleaned them all I have AC delco r43ts.. (I think) ill have to pull one and check

sixgun

When I tackle "runs but no power" issues it usually ends up
one of two things.

Spark control isn't right.

or

Air Leak into engine.

Spark control goes to the module and ECM.

Air Leak goes to some item that lets air in AFTER
it's been metered.

You have been plugging in parts, but what we haven't
done is to watch how the engine is being managed.

With a scan tool we can watch the Oxygen sensor, timing
advance, TPS, etc. An air leak would show as the engine
trying to add fuel but never achieving the fuel ratio it is
programmed for.

Any chance you know someone or can borrow a scan
tool to get more info? Note: these are NOT the same units
that do the now far more popular OBDII and CAN systems.

These older scanners aren't very expensive on say ebay,
as their day has mostly passed.

Joe

joecool108

Ive got a snap on scanner, and all the values look normal, it is the one with the cartridges you put in it, I cant remember the model number off hand. Also its hard to drive and watch that at the same time...

Maybe My ECM is bad? Ive got a spare one, I can swap and check it... I havent checked IAT or MAP sensor..

sixgun

"usually" a bad one will throw codes, but I have seen where they are messed up enough to not even report failure. If you have a spare, I think I would try it.

And yea, I know they can be hard to read while driving, but my point is/was that
the ECM is running the show, if it's doing a poor job of that you need to know.

If the ECM is bad OR the info the sensors are giving it are bad, then it may be
directing both the spark curve and fuel map badly.

Joe

joecool108

Here is something funny, this is my sons car and we swapped cars today. I drove his and he drove mine (a 91 vert with a V8) and By the time I got home, the muffler was gone.. It was a flowmaster.. He took it off yesterday to check for a possible clog and put it back on last night while i was changing the fuel filter.. well apparrantley he didnt get it back on tight enough! Hahahahahahahahaha


This is driving me crazy.. its almost like there is no advance at all and its running smoothly, but it takes it sweet time to get up to speed.... UGH!

sixgun

I just leafed through the 1990 Pontiac service manual and found that
the 3.1 has a knock sensor and ESC circuit.

If this setup detects detonation OR the knock sensor fails, the ECM
retards the spark advance to keep out of detonation.

Does your model scanner show if the system is in retard?

The Tech 1 should, I know my Brainmaster does.

This might explain your issue.

Joe

sixgun

Kingsobieski

EGR valve?

sixgun

The EGR isn't a bad thought, but they "usually" yield a bad idle and then
it becomes less pronounced with greater engine speed.

He's saying it idles nice and smooth and runs fine but just won't accelerate
very smartly.

Joe

Maverick H1L

iTrader: (8)

Check the fuel pressure... Just because the fuel pump was replaced doesn't mean the minimum 37 PSI is reaching the fuel rail (clogged filter, clogged line, rust hole, bad o-ring, etc).

What color were the plugs before you cleaned them?

Also, the next time you hook up the scanner, look at the Integrator (or BLM or whatever SnapOn calls it) number. Should be around 128, IIRC.

joecool108

The car has no EGR, and hasnt had one for 2 years, never had this problem before.Fuel pressure is 45 psi, fuel filter was changed 2 days ago. Ill check the integrator as well..
Car will idle smoothly and run ok, like Ive said it just very sluggish and has no power.. almost like its dragging an anchor behind it. Also last night I cheked the knock sensor, and the connector (plastic part that slide over with the pin in it) was missing and the wire was not connected, so I fixed it and put it back in the sensor, still same problem. I also replaced the coil but again same problem... car runs and idles but has no power up through the rpm range ...... thats why Im thinking its electrical in nature..
Oh well Ill keep trying as the suggestions keep coming through.. If I remember correctly my snap on scanner shows knock sensor reading.. Ill check that too...
I appreciate everyones help and hopefully I can get this thing running right...

joecool108

Is there a way to bypass the knock sensor.. also to run that test as described in the shop manual is a pain in the but.. engine hot.. test the sensor.. yeah right...

joecool108

Ok here are the values on my snap on scanner:
TPS .44
IAC 77
Closed loop
O2 crossover varies from 2-10
Base PW 4.5
Time 13.16
Prom 6621
AF ratio 14.7
Spark Adv 21 deg
Desired idle 913
MAT 37 deg
Mapv 2.24
Knock No
Retard 0 degrees
O2Millivolts varies 89-137 and 650-990
Rich for a long period, lean for a period. Then flicker back between rich/lean
Intergrator 180

Any thoughts ??

Also note Oxygen sensor is a 3 wire instead of the OE single wire. Since this car has headers, the O2 sensor is further down the pipe, so I added the 3 wire sensor and just ran a ground and power for the other 2 wires.

Any thoughts now on why this car has no power??

Thanks for everyones help.. Im hoping to fix this soon

Maverick H1L

iTrader: (8)

The integrator is WAY high... The ECM is trying to ADD fuel (below 128, ECM is taking fuel out, above 128, ECM adding fuel). MAPV is also a little high... Supposed to be less than 2V at idle.

If the fuel pressure stays steady at 45 PSI (holds for 20 minutes after pump shuts off), the fuel injectors need to be tested electrically (over 11.4 ohms each) and/or cleaned or replaced due to clogging.

joecool108

What would cause the integrator to be so high?
The injectors were replaced about 18 months ago with a set from Fuel injection connection (The place in Georgia) Why would they go bad in 18 months?

Maverick H1L

iTrader: (8)

If the integrator is high, the engine is pulling for more fuel. If the fuel pressure is good, you have a flow problem. Which means a restriction somewhere between the fuel rail and the pump.

The reason it's falling flat on its face when accelerating is because there isn't enough flow to keep up with the increased demand in the fuel supply.

joecool108

You wont believe after all this.. there was a wiring issue with the injector harness, apparantley when we did the timing cover gasket, the harness plug got caught (pinched) between the p/s pump, ac compressor) and must have created a short, while the thing was running, I pulled up on the harness and it smoothed out.. When I pushed it back down, it stumbled.. so we checked the harness, cleaned the connector and zip tied it up high so the xsame issue didnt occur.. and Presto! Its running normal...

Fordvette

Good so you can come fix mine now.. just kidding.. was just reading your post to get some Ideas to fix mine.. Doing much the same thing, but its a 2.8 MPFI from 1985. I swear if I dont fix it soon, Imma gonna drag its **** out and replace it.

joecool108

ok back to the same problem, it appeared again: Here are my snap on scanner values after driving the car for 20 minutes:
RPM 850
Intergrator 127
O2 Milivolts range from 168 to 943
Closed loop
TPS .44
Block learn 113
IAC 33
Spark Adv 20 degrees
desired idle 850
coolant 83 degree Celsius
MAT 40 degree Celsius
MAP kpa 35
MAP V 1.3
Baro km 103
baro V 5.02
knock n
Bat 13.6
fuel pressure 13.6 v

Injector harness checks at 5.8 resistance but car has been running for 20+ minutes.

As I drive it when it sputters and stumbles here is what I notice: TPS,IAC, spark advance all stay steady, they don't jump around, so im not sure what's happening. I do notice however the car runs rich and the O2 sensor voltage stays over 1000mv and doesn't fluctuate.. this only happens under load, in the driveway it doesn't have the same issue.

Any ideas? Fuel filter was replaced yesterday.
Could I have another bad set of injectors? I've already replaced them twice...
HELP!

joecool108

Latest update, Ive checked all the injectors and they are at 14.8 so they test good.

antares57

iTrader: (8)

Have you checked the FPR fuel pressure regulator. Is it bleeding fuel into the vacuum hose? When mine had a ruptured diaphragm I didn't have any power at all. Would run, but not well.

joecool108

yes, I checked FPR, when I pull the vacuum hose off there is no fuel in the vacuum hose. I even let it run for 1 minute with the hose off and no evidence of fuel coming out. Is there any other way to check it? Would the FPR cause it to run like its on 4 or 5 cylinders sometimes?