350 TPI Missing at Idle....
Thread Starter
Instructor
Joined: Apr 2002
Posts: 169
Likes: 2
From: Newark De
350 TPI Missing at Idle....
Hey all,
I have a 350 TPI in my 1988 IROC Z and I'm having an issue with it missing occasionally at idle. The car runs fine going down the road, but when it sits at a light in gear, I get the occasional miss.
I had this when I bought the car and replaced a bunch of parts. The last thing I did was replace the injectors about two months ago with Bosch III's from FIC and that seemed to fx the issue. Now its back again. Any ideas on what to check next? The car runs fine but its annoying sitting at a light. List of replaced parts and work performed:
MAF
plugs
wires
distributor
cap
rotor
PVC valve
injectors
all intake gaskets
cleaned IAC
set timing to 6 degrees
set TPS
FP regulator
fuel filter
Any help is appreciated!
I have a 350 TPI in my 1988 IROC Z and I'm having an issue with it missing occasionally at idle. The car runs fine going down the road, but when it sits at a light in gear, I get the occasional miss.
I had this when I bought the car and replaced a bunch of parts. The last thing I did was replace the injectors about two months ago with Bosch III's from FIC and that seemed to fx the issue. Now its back again. Any ideas on what to check next? The car runs fine but its annoying sitting at a light. List of replaced parts and work performed:
MAF
plugs
wires
distributor
cap
rotor
PVC valve
injectors
all intake gaskets
cleaned IAC
set timing to 6 degrees
set TPS
FP regulator
fuel filter
Any help is appreciated!
Instructor
Joined: Jul 2007
Posts: 236
Likes: 0
From: Mobile Alabama
On your miss
Of course you'll want to check the throttle body and make sure it is very clean, make sure of all things the battery is good and connections good. Other than that you've done everything - will just have to recheck as you may have gotten a defective part along the way. Hope it helps some.
Melting Slicks
Joined: Jul 2005
Posts: 2,221
Likes: 302
Ahhh, the dreaded idle misfire... I struggled for a few years with mine. I did all the same things you did trying to diagnose it. Turned out I was losing compression on the number 7 cylinder, found during a leak down test. Determined it was leaking through the rings. In a last ditch effort before I pulled the engine, I ran some Rislone compression repair and put it in the oil. Damned if it didn't solve the problem! I think I had sticking piston rings and this stuff freed them up. I put the additive in, ran the car for a couple hundred miles and the misfire just disappeared over time. This was a couple of years ago and hasn't been back since.
Like yours, the leak was just enough to notice it at idle (where the leak rate was a high proportion of the total incoming A/F mixture), but once I was up to speed it wasn't noticeable anymore.
Strongly suggest you run a leak down test on all your cylinders.
Like yours, the leak was just enough to notice it at idle (where the leak rate was a high proportion of the total incoming A/F mixture), but once I was up to speed it wasn't noticeable anymore.
Strongly suggest you run a leak down test on all your cylinders.
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Race Director
Joined: Aug 2000
Posts: 14,130
Likes: 7
Cruise-In II Veteran
You can use the timing light on each of the wires one at a time, while its running and it may narrow down which cylinder its missing from.
I use the light and rev the engine by hand,holding the trigger light down and watch for gaps and misses in the light flashes.Real easy to do and works well.
I use the light and rev the engine by hand,holding the trigger light down and watch for gaps and misses in the light flashes.Real easy to do and works well.
Thread Starter
Instructor
Joined: Apr 2002
Posts: 169
Likes: 2
From: Newark De
Ok guys, I haven't done it all but here's what I have done so far. I apologize for taking so long between posts, just been busy here.
Dropped the timing from 6 degrees to 4 and then 2. Seemed to help for a little while but now its back. Car was slightly pinging when I gave it heavy throttle at an observed 6 degrees so I thought maybe the balancer had slipped and my timing was excessive. Car was alot more sluggish with 2 degrees of timing. Also disconnected the timing wire with no change.
Ran a can of Seafoam through it. Did nothing.
Tried the timing light trick on each cylinder. When the car was stumbling or missing, all plugs seemed like they were firing correctly.
Throttle body is clean as I cleaned it all up when I did the injectors about 4k ago. All of this went away when I did the injectors and resealed the intake..........Maybe I have a bad injector?
Next thing will be the compression test, but I don't have a leakdown tester. I just haven't done that cause its such a job on one of these cars........
Going away this weekend, so maybe I can do it next weekend or at least one night during the week.
Dropped the timing from 6 degrees to 4 and then 2. Seemed to help for a little while but now its back. Car was slightly pinging when I gave it heavy throttle at an observed 6 degrees so I thought maybe the balancer had slipped and my timing was excessive. Car was alot more sluggish with 2 degrees of timing. Also disconnected the timing wire with no change.
Ran a can of Seafoam through it. Did nothing.
Tried the timing light trick on each cylinder. When the car was stumbling or missing, all plugs seemed like they were firing correctly.
Throttle body is clean as I cleaned it all up when I did the injectors about 4k ago. All of this went away when I did the injectors and resealed the intake..........Maybe I have a bad injector?
Next thing will be the compression test, but I don't have a leakdown tester. I just haven't done that cause its such a job on one of these cars........
Going away this weekend, so maybe I can do it next weekend or at least one night during the week.
Thread Starter
Instructor
Joined: Apr 2002
Posts: 169
Likes: 2
From: Newark De
So I finally got around to doing a compression test today. While pulling the plugs, this is what I found on the number 7 cylinder and its as far as I got. Any ideas as its obviously the cause of my miss.....
I was thinking of a cylinder head gasket myself.....
I was thinking of a cylinder head gasket myself.....
