got a 350 tbi that was running a lil rough last summer but just lived with it for the duration of the summer. Spring is here and I want to track down this problem before its time to hit the road. It's a rebuilt motor, with just a very mild cam. Otherwise, its stock. Once it warms up a little, the idle will drop down a bit and then it starts to run with a little miss. I have dual exhaust on it and its misfiring out of both tail pipes. Sometimes at a stop light it will stall but fire up right away. Tune up components are all new, IAC valve is replaced, tried a EGR valve, tps and ignition module and coil and a new temp sensor. I can't help but think its a timing issue. When the engine was assembled I know for sure the timing marks were lined up on the timing gears and the #1 piston was at TDC. Just to be sure I set it at tdc #1 but the timing mark on the balancer is sitting at the 12 oclock position. if the distributor is turned to get the mark down to 0 degrees it falls on its face and dies. wondering why the mark is sitting at 12 o clock and not on the 0 degree mark. Any ideas?

 

First thing I'd look at are the injectors in the TB. I had same symptoms with my TPI, did every sensor, tune up, plugs wires/distrib ... tuned out to be 2 bad injectors.

Idled smooth as silk, then idle dropped and it ran like a grizzly bear. After new injectors smooth as could be. Can you ohm out TB injectors ?

Go on youtube and search ohming injectors.

 

Factory timing mark should be at 12:00 position. Aftermarket timing covers and earlier SBCs had the 2:00 position. You need the correct timing cover matched with the correct damper or you will not get accurate timing with a light. One option is a damper cover with timing marks on it.
http://www.summitracing.com/parts/pr...Fa5DMgodg04AzA

 

gunna go in the shop tonight and take a peek at the injectors. think I got a spare set kicking around to try also. I do have an aftermarket timing cover and indicator on the engine. could I just get the engine at #1 tdc and make a new mark on my balancer?

 

A piston stop is a much more accurate way to determine TDC. I imagine you could get within 5-10* that way.

 

Hows the tune up parts? Wet the ign. wire down in the dark. Whats the fuel pressure, these tbi engines will run on very low pressure, just not very good.
Tight rocker arm lash? Kill each cylinder at a time till you find the ones that aren't contributing.
Make sure the distributor shaft isn't loose.

 

all tune up parts are new and late last summer even replaced everything under warranty just in case, fuel pressure I bumped up to 15-16 psi. Gone over the pushrod lash 3 times to be certain. Distributor was replaced with a known good one. I know how the knock sensor works, but if you tap on the block would you hear the engine alter its timing or is it only noticeable by timing light?

 

did a resistance check to both injectors, I got 0, perfect continuity........and I know those are supposed to be around 1.3-1.5 ohms. could this cause my engine to misfire on both banks?

 

well injectors did nothing for me. but while I was playing around with the timing light I noticed the light stop flashing periodically on multiple cylinders. The timing mark doesn't jump around barely but there is definitely something going on with the ignition system I think. Wondering if this could be an ignition module issue or a distributor issue? I've swapped out complete distributors before but only with used components. Any ideas?

 

well been playin with the car tonight and still going back to an ignition problem. tried grounding wires to narrow it down but its real hard to nail it down to what cylinder is messing up. without the use of an oscilloscope and just using my timing light, most cylinders are firing regularly. But some repeatedly don't. I've put the lead close to the plug and close to the distributor and the same cylinders keep acting up. here's what I got by rough percentage of what their contribution is..... #1 25% #8 75% #4 90% #3 75% #6 90% #5 90% #7 50% #2 25%. Again, just going by how the timing light is flashing but I don't really see it being a timing light issue cuz I hooked it up to my other 2 vehicles that are running perfectly and the light never misses a flash. What could be causing this? a bad pickup coil? I really think its somewhere in the distributor area. Any input?

 

I have never heard of anyone using a timing light to check for cylinder misfire, I have been in the automotive business for over 20 years, what are you trying to do with that timing light?

if you wanna see what cylinder is firing and what one isn't, pull one wire at a time from cap or plug, if engine shakes worse that cylinder is firing, if it doesn't change, that cylinder has an issue, to check plug wires, just get a spray bottle and spray water on each one to see if engine idle changes,

please explain the timing light process you was doing, Ive never heard of that method before

 

just trying to monitor the firing of each cylinder. and without a scope this is the best I can do lol. the problem is that each of these problem cylinders is so intermittent that I can't narrow it down by killing a cylinder at a time. On the same cylinder, sometimes the idle will change, and sometimes it won't. all tune up components are new and not leaking.