gta_knight

So my 91 Firebird had idiling problems and when driving a huge sputtering problem that was pretty much constant when giving it gas just to move the damn thing.

I diagnosed a big vacuum leak from the back of the intake. I also ohm tested the injectors and the results were pretty terrible.

So new set of injectors from South bay. New fuel pressure regulator. New gaskets of course. Also a new MAP sensor as it had previously threw a code for that but possibly was due to the vacuum leak I found on the intake. Also a new throttle position sensor and idle air control valve.

put the car all back together this afternoon and it started right up. Great. Checked for leaks and there were none. Also great. It was idiling just fine too.

let it warm up for 5 minutes then I thought I would take it for a spin around the block to see if the problem was solved. NOPE! It felt worse acrually. I reversed off my driveway, put it in drive and as soon as I set off i could feel it. Then a bit more gas and it was sputtering and everything. Nearly cut out as I turned around and headed back home. Parked it on the drive and the engine idle was intermittently going up and down on its own too.

what in the hell is going on.... any help greatly appreciated!

OrangeBird

iTrader: (1)

Hi gta_knight, on the 3.1 engines there is an IAC "relearn" procedure that your supposed to do when replacing the IAC. I don't recall the particulars but if you search "Relearn" here you should find posts discussing how to do it.

gta_knight

already done that so that's not the issue unfortunately. I tried it again as it was getting dark and had the lights on and they flicker. The dash clocks and the interior light etc. If I press the brake the dash lights get dimmer too. Im not sure if this will be related to the cars sputtering and no power or not but I will have to check the earths etc

cosmonautpg

Have you made any voltage measurements yet? Check between the battery terminals as well as between ground terminal and alternator and see if there’s a large difference in the readings. Try it also with a load on the system (light, ac on). If there’s a problem with the power generation (or the grounds, like you mentioned) it can definitely affect the ability of the engine to maintain a spark.

gta_knight

It was charging at only 13.1 volts, i cleaned the ground connections for the alternator and it was back up to 14.3 volts and the dash lights and interior light had stopped flickering too.

gta_knight

So here is where im at as of tonight. Tested the fuel pressure again and i get 40psi with the key on and it doesnt leak down to zero anymore. so im guessing one of the old injectors was stuck open. with the engine running its steady at 38psi, it doesnt change if i rev the engine, not sure if it should or not ??

i then moved onto the timing, it was at 0 degrees !! so i unplugged the connector and set it to 10 degrees, switched off, reconnected etc and...no difference. unbelievable. It was idiling ok, i could still see it was still sort of misfiring as the engine wasnt totally smooth and the rpms dropped a little after it had been running about 10 minutes.

I took the dizzy cap off, it seemed like a fairly new one but it had a little bit of build up on the rotor arm and inside the cap so i cleaned that off. inside the dizzy itself is a bit corroded around where the pickup coil is housed so im not sure if that could be the problem or not? spark seems fine so im guessing its not to be honest.

Its had the EGR valve deleted, however there is a brand new one in the box that came with the car? it looks like its been deleted for a while by the colour of the blanking plate. im guessing that needs written off the ECU to run properly, im half tempted to bolt this one on and plug it in to see what happens?

85Z28NOS

iTrader: (2)

If the EGR has been removed and the chip has not been modified it will affect the way the car runs

gta_knight

yeah I know. It's thrown no error code relating to the egr though so I am assuming it was deleted from the ECU. But someone has bought a new shiny one and it came with the car. Could be worth bolting on and plugging it in to see if it makes any difference?

Whitebird75

Have you check the timing? remember to unplug the connector on the passenger side, or the timing will be way retarded. Base for the V6 is 10* BTDC, as the V8 is 6* BTDC. Also, have you checked the fuel filter?

tealman92

How many miles are on the engine? Have you taken a look at the timing chain set to see if its stretched?

gta_knight

it's only done 77k ! I moved the nut back and forth with the dizzy cap off and the rotor moved in time

gta_knight

yup I fitted a new filter. Also set the timing. When I checked it it was at 0 degrees so I thought great that's the problem. Set it at 10 but no different!

gta_knight

So the newest thing I've noticed while checking stuff was the interior light and dash lights were pulsating in time with the misfire.

the battery was only charging at 13.4. I cleaned the ground connections at the alternator and it was then charging at 14.4 and no flickering lights. However I noticed it was doing it again last week so I'm not sure what's going on there?

gta_knight

More investigating today. Had a vacuum gauge on and it was just in the ok section. It would move properly into the ok section I advanced the timing. However the timing is bouncing around...

A friend of mine came over and checked the knock sensor. He got virtually nothing from it when OHM testing and nothing when tapping it with a hammer to get a voltage output! We unplugged it with the car running and the timing went close to 10 degrees and it was actually running a bit smoother.

So after all of this it could just be a bad knock sensor??

Whitebird75

Make sure that you unplug the EST connector before setting the base timing. If not, you will be chasing the timing all over the place.

gta_knight

Latest update. The knock sensor was suspect so I've replaced that. I hadn't driven the car since replacing most of the parts so it's hard to say what has cured the driveability issue but I took it around my street a few times today and driving around it feels fine now. No hesitation or intermittent cutting out when going near the gas!

the problem remains at idle or really low speed. There still this misfire and it randomly drops RPMs then recovers now and then.

I'm seriously running out of ideas now!

Pupkin

Same problem. Did you find the reason for the crap running?

gta_knight

Nope it still does it and I've go idea why at all. I'm still doing tons of work to the car so it's never been out of my street yet. The few times I have drove it around it feels fine. Its just when you come to a stop and put it back in park it does the weird idle thing.

I've just left it alone for now as its not really causing any problems. Just dropped a few hundred rpm then picks back up

Pupkin

Thanks. Have you ever tried to log the ALDL data with the TunerPro software when it is running bad?

gta_knight

I actually bought a cable someone has made but I don't have a laptop with a serial port lol.

Pupkin

Oh, ok. I am using an old Toshiba Satellite 320CDT laptop in order to log the data. I think there are other or more laptops you can use for logging.

Mark RWC

USB to serial adapter to add a serial port on newer pc or laptop without a serial port. Tripp Lite makes a USA19HS usb to serial adapter that works well. It can be found online at ebay etc.

1989karr

Is the pump original?? Kinda sounds like the fuel pump can't perform when the fuel demands are increeased...but it does ok at idle.



Would suspect fuel pump on its way out....my TPI and S-10 did this! TPI was wrse case it actually crappped out 100 percent in the middle of the road lol

maroe624

Ah the trusty 3.1. Love that little engine. I would start with a nice ignition system rebuild. Cap, rotor, plugs, wires, pick up coil, ICM, and ignition coil. If that doesn't fix your issues then you have an vacuum leak. Check the plastic lines going to TB. Check MAP lines. If that doesn't fix it then ohm check your injectors. Replace if needed.. Pull line off the FPR and if you smell gas its bad. Car will run fine without egr hooked up. Most common problem with the 3.1 is a bad icm. If your car runs hot then it will sooner or later kill the icm. Check grounds on both heads make sure they're not loose. Got the beasty v8 under the hood but got a sweet spot for the 3.1 . If you come across an 92 RS 3.1 T5 stick car lmk.

gta_knight

Everything mentioned above I've pretty much taken care of now. New injectors. Fpr. All the engine sensors including the knock sensor. Tried 2 other ecu's even!!

The car seems to run and drive nice and smooth but I've still never taken it out of my street as its not road legal yet. It still drops a few hundred rpm after it's warmed up slightly idling on the driveway. Idle drops....then gradually picks up and then does it again a few minutes later etc.

However when you stick it in drive and set off it seems fine. The real test will be when I have to drive it for it's MOT test we have here in the UK as the garage is about a 15-20 minute drive from my house so if anything goes wrong it will no doubt happen on it'd maiden voyage lol

gta_knight

Fuel pump is new a couple of years ago. Previous owner cut the trap door which he didn't tell me. He just said it had a new pump fitted. It's nice and quiet at least and the fuel pressure is bang on when checking with my gauge. It was dropping to zero after the ignition was switched on but I soon found I had a stuck open injector

1989karr

how is it when revving? mine would idle fine but when revved it couldn't peform etc... so theres i think idle peressure etc... and a revved pressure?