Ignition/Starting Woes with recent 3.4 TDC engine swap

[iambhooper]

I have swapped a '92 3.4 TDC into my '86 Fiero GT 5spd. I am using the 9396 ecm and have had the memcal reprogramed. The car was running good, while still having the bugs worked out of it.

After having the car down for a month (working on a P/S pulley eliminator), I have had difficulties getting the car to crank. It turns over, and even fires (or stumbles trying to fire), only to die within a few seconds.

I believe the engine is getting fuel (using the v-6 Fiero's fuel pump) as I hear the pump cut on and off, and can smell fuel.

I have checked for spark on the coil/module set and found some interesting results... Cyl's 1 and 5 showed no spark. When I sapped to another coil/module set it showed no sparrk on cyl #6.

Thinking I had a bad coil on the second module, I swapped in the "good" coil from the 1st module. This resulted in a lack of spark on cyl#1.

Having checked all the wiring, I noticed that I had left 2 wires fromt eh Fiero's VSS disconected to the ecm (the fiero's signal goes directly to the Speedometer, yet the TDC's ecm requires input from the VSS). Hooking these back up resulted in the car crankng.

The car ran for about 3-5 minutes, while I topped off the coolant system. However, the engine shut off on it's own. Afterwards it is experienced the same symptoms as b4.

Is this a dead on result of a faulty control module, or is it something else? Even though I did this swap, I am no mechanic. However, as I understand the DIS ignition system, there is very little to go wrong, right?

any input is welcome!

[jmgtp]

Re: Ignition/Starting Woes with recent 3.4 TDC engine swap

I noticed you say somewhere in there that cylinders 1 and 5 showed no spark? Maybe you have the wires mismatched, as I believe IIRC, that cylinders 2 and 5 share the same coil. So if cylinder 1 has no spark then cylinder 4 (they share the coil) should also have no spark. If cylinder 1 were to have spark and cylinder 4 not to have spark that means that the problem is in the wires. I guess what I'mm trying to say is if you havent checked already see that cylinders sharing a coil either both have spark or both dont have spark. Sorry if my logic was difficult to follow and forgive me if I have misunderstood.

If it turns out that you decide to replace the ignition module I suggest giving ebay a look. I recently bought an ignition module complete with the 3 coils from a 3100 engine for $10. I see them often on ebay in the 30-50 dollar range, I think I just got lucky with the $10 steal. (I searched for 3.1/3100/3400 etc).

good luck,
-john

[iambhooper]

thanks for the quick response!

sorry if i was complete enough in detailing my trouble shooting. what you suggest makes sense, except that i did check all the cylinders.

here's what i found (left to right):
module #1
cyl #... result
1 no spark
4 spark
6 spark
3 spark
2 spark
5 no spark

module #2
1 spark
4 spark
6 no spark
3 spark
2 spark
5 spark

module #2 with the #6/3 coil replaced
1 no spark
4 spark
6 spark
3 spark
2 spark
5 spark

on module 2 i replaced the "bad" 6/3 coil with the "good" one from module 1.

if i buy a new module, i will buy one new. my spare came off of a 3100 for $20, with all the coils. a great deal... unless it's preventing the car from running.

i've changed out wires, plugs, modules, coils, crank sensors, and pulled the wiring harness... all to no avail.

[grandprix34]

wait, so the coil module + coils on a DOHC are the same ones used on the 3100/3400/3.1 ???? WOW!

[jmgtp]

here's what i found (left to right):
module #1
cyl #... result
1 no spark
4 spark
6 spark
3 spark
2 spark
5 no spark

Hmmm... very odd. Cylinder 1 & 4 share the same coil. If #1 has no spark #4 should have no spark, unless the wires are bad (jumping spark somewhere before the spark plug) or hooked up to the wrong cylinder. I know I just sorta said the same thing as my last post but I think the problem has to either be wire routing or bad wires, unless its possible for a coil to go bad in such away that it delivers spark to only 1 of its terminals?? that I do not know.

You could also test the coils with an ohm meter across their terminals, I got something like 5.3k ohms on each (IIRC).

-john

[Cliff8928]

Maybe it's possible that the crank sensor is on it's way out? I thought they ususally just die... but it's en inexpensive and common problem..


Cliff Scott
89 BerettaGT
89 Volvo740

[iambhooper]

i tried a new set of wires... no difference (the wires i had on the engine may have 500 miles on them period).

i tried a new crank sensor (see above)

and today, i tried a new module... no difference. (of course i didn't have a chance to check the spark, b4 i had to leave)

***9:40 PM*** I checked the spark on each tower of the coil... it is definatly there. It's possible that I didnt' crank the car long enough to see the spark, earlier. Either way, the car is no starting.

would fuel pressure cause this? i'm a little concerned about the bracket that was made to eliminate the p/s pump... it bolts to the back bolt on the plenum, and puts considerable pressure on the schrader valve.

thanks for the help... maybe somehow we can fix this thing!

hoop

[iambhooper]

update... it appears the problem wasn't ignition related. it was fuel pressure. best i can tell, the schrader valve on the fuel rail was under pressure from the bracket, and this was causing it to open the valve.

i have that fixed and the car is running. i need to debug some wiring issues. the car is idleing high and the coolant fan funs constant.

thanks for the help!
hoop

[jmgtp]

the coolant fan funs constant.
hoop

Likely there is no signal from the temp sender in the lower intake manifold. harness unplugged or bad connection?

[iambhooper]

i think there's more to it than that. considering i'e spliced 2 harness's into one.. i've probably missed something somewhere.

given time, i'm going to get an extra set of harness's and build a new one for the Fiero.

hoop