What could cause a TPI motor to "run-on" for a second or two once the key is turned off? It doesn't always do this, but it does do it which may be related to the miss the engine has which is worse at some times than others and a rich smell coming fom the exhaust.
The timing is right at 6 degrees at idle with the set timing connector disconnected and I've confirmed it many times now.
I am familiar with a carbed engine doing this because of either timing or carb adjustments, but I'm at a loss as to what to try on a system that has so many sensors and a computer dictating it all

I am beginning to wonder if the computer I have has failed and maybe I should just swap it out.
Would a person still use the exisiting 'chip' from the original computer, or is that where they fail?

Recap:

-Rough idle which is worse at times
-hard cold start at times but other times it fires right up with the bump of the key
-engine seems to have a bad miss at times, then other times it doesn't
-engine will sometimes "run-on" for a second or two once key is turned off, but again not all the time
-exhaust does have a heavy smell to it, which I'm guessing is a RICH condition


Any ideas?

 

FWIW, I have tried to search for some answers, but of course you get a 99% return of threads that have absolutely nothing to do with what I am looking for.

Was hoping maybe a senior member or someone with a little experience with diagnosing TPI would chime in.

My car is completely driveable, I just know something isn't right.

It ran fine for 2 years until recently.

Whats the best way to check for a vacuum leak?

 

I think the only way your going to get engine run on with TPI is leaky injectors. To check for vacuum leaks I like to use a bottle of MAP gas and go around all the lines and everything with it listening to the idle. Some people like to use carb cleaner but I find it tends to get a little messy.

 

Leaky Injs has my vote also

 

What is your engine idling at when you shut it off and this happens? I had an 87 GTA that had a dieseling problem and it was due to a combination of running hot and a high idle. Look in a Haynes manual in the first few pages where it gives symptoms and causes and check out the one for engine dieseling and see what it suggests. I'd go read it and tell you, but my manual is clear out in the garage and I am lazy today.
If you think it's a injector problem, Go through and check all of your injectors with an OHMmeter and see what kind of readings you get.
Good luck.

 

If not injectors check your fuel pressure; could be a bad FPR.

 

Thanks guys for all the replies

Up until now, I have already installed another FPR because recently I had a problem of losing fuel pressure after shut down and low fuel pressure at idle. I pinched off the return line and it held steady pressure, so I changed the FPR to an adjustable one. I now have ~43lbs~ at idle and it holds once key is turned off (fuel pressure was @ 35lbs before FPR change).

I have verified 6* timing at idle many times with the wire disconnected.

I 'adjusted' the IAC twice.

I have set the TPS to exactly 0.54v even though it was already 0.52v.

Injectors all ohm out good(15.5-16.5), even when hot.

 

Well, I'm about to just consider this a fuel injector issue since I tried swapping out the computer and it didn't change anything. In fact, for whatever reason, after I swapped out the computer and started the car just to find nothing had changed I also found that the car didn't even want to stop running for at least 5 seconds after the key was shut off

I am going to once again hook up the fuel pressure gauge and see where the pressure is, but since I've done it several times now I am confused at the fact that I am showing a steady pressure even after shut down.
I'd think that a leaking injector would show an obvious loss of fuel pressure.

I do have another set of reconditioned injectors, but they are 22lb ones.
What would happen if I tried running them on a stock MAF tune for a 305 engine without changing anything else?

 

Well, after hooking up the pressure gauge it now does in fact show the pressure slowly bleeding off after shutdown. I tried to loosen up the screw in the AFPR and noticed that gas is seeping out around the adjustment screw. I'm sure that shouldn't happen, should it? Also, I noticed that a little gas was even making its way through the vacuum line on the regulator.
With the rubber diaphram, gas should never make it to the 'top' section of the regulator housing, correct?
I can't believe this diaphram is bad already.

If anyone can confirm anything I've just asked, PLEASE take a minute to reply so I don't have to start yet another thread trying to get an answer.
Thanks.

 

You can definitely run 22lb injectors in a 305 but you may not receive optimal performance and or miles per gallon

 

Thanks southbay08 for the reply.

 

Our pleasure!