I spent a whie now searching the boards for solutions to my problem but I'm going to post up my symptoms to see if anyone has any ideas

The car is a 87 350 TPI.

Symptons are :-

- bad misfire on idle , getting increasingly worse. This morning it seemed to be missing on a few cylinders although it isn't constant

- When the revs are raised it does clear a little but i can still feel a slight shudder / misfire every now and again.

- car wouldn't start at all a few weeks ago, tried again about an hour later and it fired up no problem. I've not encountered this problem since and it starts fine.

- misfire is from start up and there is no difference whether the engine is hot or cold.

- hesitation sometimes when pulling away from a stop.

- no SES lights

things I've tested

- Compression check showed everything is fine.

- ohms test on injectors showed up fine, although I appreciate there still could be blockages.

- No obvious vacumm leaks, listened to engine with tubing and also sprayed easy start around.

- I've got spark to all plugs and i've tried pulling each lead to narrow down search but its an irregular misfire and doesn't seem to be affecting a certain cylinder/s

- dizzy cap, rotor arm, plugs and leads are new.

- I've reset IAC, and there was no difference

Planned next steps are

- check dizzy, I'm thiking the gearing could be shot ?

- check coil although i'm doubtful on this one as i would expect to get a real bad running prooblem on high revs under higher load ?

Anything anyone else could recommend checking ?

I live in the U.K so its difficult to test parts by swapping things over

Thanks in advance

 

I stripped the dizzy out tonight an its shot.

 

whats a dizzy and how did you strip it out?? My cat acts up similar to yours. Have you had any luck? Im wondering about my coil or fuel supply.

 

I changed the distributor and its still bloody misfiring ???????????

Any thoughts guys. its not an horrendous misfire but its certainly getting on my nerves. I've been told to use some injector cleaner ??

I thought about coil but I'm sure the misfire would get worse on high rpm's due to load but mine smooths out if anything.

 

Do you have good fuel pressure? Normal should be around 42 PSI

 

Mine is basically doing the same thing. 89 TPI. About 500 miles on rebuild. Bad miss but smoothes out on acceleration. It will come back when the speed levels out but not as bad as lower speed/rpms. It started about a month ago and has steadily gone downhill.

I just ordered a set of injectors that should be in tomorrow. That will eliminate one thing that I think is most likely. $169.00 USD for a set of 8 Bosch III upgrade from http://fuelinjectorconnection.com .

What I believe is happening at this point is leaking injectors. A lot of fuel smell behind the car.

If the miss is from the ignition system it should get better with a rise in rpms. But this does not rule out other problems. If your dist, cap, rotor, plugs, plug wires, coil are good, and it is timed right, then you probably have another problem. Also, from past experience, an ignition miss doesn't get this much worse this quick (yes, there are exceptions). Usually it just continues to miss.

Something I am checking today is the MAF burnoff relay. Although I do not know the specifics on how a MAF with a dirty wire effects the running.

 

I'm almost sure mine is timing related.

I disconnected the tan wire next to the firewall and then set the timing at 6 degrees BTDC and it ran lovely, very smooth. I then turned it off and nipped the distributor up and then hooked the tan wire back up and the it ran like a load of sh*t again. I made sure the distribuotr didn't move when tightening it up

I spoke to a buddy of mine and he said that the timing needs to be set with the car in drive ? is this right. I set mine up in park. so could this be my problem when i reconnect the tan wire ????

 

no - the timing does not need to be set in drive.

hooking the wire back up allows the ecm to control the timing.

I'll let you know how mine turns out with the injectors. I reread your first post in this thread and it sounds exactly like mine. I suspected the injectors even before this started to get worse. They are factory, about 120,000 miles on them. Everyone says they are junk. So, at best they are very old junk now...

I am reasonably sure it is the injectors so I won't even check anything else unless it turns out to not be the problem. It may even be multiple problems, and doing too much all at once won't help in diagnosis later.

I am willing to change everything out as I do not know the history of any of these parts. I bought the car as an engine donor and just reused all the sensors etc. Of course I will keep what I can.

 

can anybody answer why my car idles nice with the EST wire unplugged but has a bad idle when i plug the EST wire back in ??????

 

Just noticed that the coolant switch sensor on my passanger head connection has been smashed off so could this be the problem ?? I've ordered a new one that should be here in a couple of days so hopefully that will remedy the problem.

 

I'm pretty sure what you are referring to is just the sending unit for your temp guage. That should have no bearing on how the car runs. Your true coolant temp sensor is located on the front of your intake manifold. Shown here....

 

I was sure it was a fan switch of some sort, its on a dual fan '87 camaro.

 

If you are talkng about the switch near the rear of the passenger head under the exhaust ports and above the starter, then it is the fan switch. It is a switch to ground and will cause no problems other than overheating.

Sending unit to the temp guage is on the driver head.

The injectors came in today, but I may not have time to change them as the wife just split to go to the store where they sell "beauty products" - you know, "the necessities of life" things. Thank God the 8 injectors look like cheap toys - she didn't say a thing.

 

Okay mate.

I'm sure mine isn't the injectors because as soon as i disconnect my EST wire the car runs fine on idle. Its only when i re-connect the wire that the idle goes rough again.

Really need to get this sorted. Its drivable but it is a problem that is bugging me bad

Anybody know where i should go from here ?

 

Okay I've checked and I'm throwing codes 33 and 42

------EDIT--------

Okay I didn't reset the computer after disconnecting the MAF and EST hence the codes. I rest the computer and no codes are now showing.

HOWEVER. I checked the timing with the EST connected and it is about 29* and it jumps ALL over the place my rev counted also is is all over the place and jumps between 600 - 1100

does this indicate anything ??

 

JUst checked timing again with the EST connected and its all over the place on idle and at around 26* to the left of the 0 mark ( i presume thats advanced ?) when my friend brought the revs up to around 2000 rpm the mark lines up and sits perfectly on the 0 at around 29 *

 

Did you find the problem?

 

Not yet mate

I've order a VOM and it should turn up tuesday. I'm going to check some of the circuits around the EST and ESC unit.

I really dont understand why the timing jumps all over the place at idle but sits perfectly on the mark when you bring the revs up, dodgy sensor maybe.

 

Have you checked the TPS? Cleaned the IAC? I see where you reset the IAC.

If the computer thinks that your throttle position (TPS) is higher than it is it will try to adjust other things accordingly.

There is a good write up on cleaning and adjustment of TPS and IAC here:
https://www.thirdgen.org/forums/tpi/...?highlight=vom

Throttle Position Sensors seem to be fragile things especially if they get wet. I just pull these off to wash the engine and then reinstall. The TPS can be bad at one point of the range and good at the rest.

 

Thank you for the link.

TPS was next on my list when i receive the vom

I'll let you know how I get on

 

im having a very similar problem however it only occurs when warmed up between 600-1000 rpms and sometimes on acceleration.. ive cleaned my iac and passages in throttle body and my tps is set at .71 and maxes out at 4.30 at wot (90 SD 350) let us know what you find

 

Will do

I wont be able to do much for the next couple of days but i'll let you know what i find as i find it.