Swapped 3.4DOHC wants to die when shifting

[pocket-rocket]

BCFA is the code/tune for the LQ1/5 speed cars.

[Dave96z34]

The fuel rail was installed back words on the engine..... Fuel lines on Fiero on the drivers side?

[dedgar]

Fuel rail is mounted so that the pressure regulator is on the passenger side.
Upper intake is to the rear. Throttle body is on the driver side.

[Dave96z34]

I would change that regulator or re route the lines so the fuel rail in on the correct side of the engine.

[dedgar]

I'll worry about the fuel lines later. I want to get this so it doesn't want to die when I pull up to a stop or between a delayed shift.
And I guess no one here can provide a picture or some such that shows where the sensors are supposed to be.
I have a Haynes manual and it does show engines that are available and sensor locations for those engines EXCEPT for the 3.4DOHC. It isn't included.
As stated before, it start and idles like it should. Has good power and revs rapidly. Fuel mileage I had hoped would be better but I don't know how much better that it should be.

[gsnickle]

I do agree with the diagnosis path, but I may have another path for you to look at. When I did my first TDC Fiero swap I could not find an ECU for a manual TDC, so I used a 93 auto ECU (93 was the last year for non-computer controlled auto trans). This did not have compensation programing for when the clutch is pushed in on deceleration. This combined with a light flywheel, lack of PS, underdrive pulley, etc (lower rotational mass) leads to a stalling problem when warm. I would make sure that the programming is for a manual chip and not an automatic.

The second problem that I ran into was when I mated the engine to the Fiero transmission (Izusu 5 speed) there was an incompatibility between the 87 VSS and what the 93 ECU was looking for. This caused a rich condition (not massively rich) and stalling under decell and coasting. This was linked back to the ECU using different map adjustments for idle request while moving and idle request while still (or close to still). You may have to use the VSS signal mod or I think that somebody figured out a way to do it with a wire harness mod. The mod is either on this site or on Pennock's Fiero Forum. You should be able to see this in the codes, it shows up as a VSS failure or VSS out of range code.

As a side note, if the engine is running correctly in stock trim, your Fiero should get between 31 and 37 mpg on the highway. It sounds like you may be running a little out of spec to only equal the 2.8 fuel mileage.

thanx

[dedgar]

When you see the VSS codes, is that a check engine code flash or when doing a scan?

[gsnickle]

Usually it will show up as a steady SES light when throttle is steady above 15 percent throttle (cruising the highway), but if the person that built it reprogrammed the ECU, you can tune this failure out of the SES display. Do you know what year your ECU is? If they used a 96-98 ECU it is OBD-II, and if they did not tune it correctly many problems can be lurking in there. Some people find it easier to turn off the warning than to fix the problem.

[dedgar]

No SES codes and no codes stored according to the scan program I'm using.
I was told the ecm is from the '93 the engine came out of.

[gsnickle]

Do you know if the ECM is for an automatic or manual, and what transmission is being used in the car? Is it an Izusu or a Getrag, or is it the very rare 5 speed that came with the 3.4 TDC?

[dedgar]

As far as I know, the original car was an auto and that is where I was told the ECM came from. It is currently attached to my Getrag.
What did you have to do to get the engine to stop wanting to stall? Or did you get it to stop?

[robertisaar]

the 91-93 3.4 used the same ECM for automatic and manual. the difference between them is the MEMCAL, which should have been dealt with when the tune was done.

[gsnickle]

I changed the memcal to a manual stock programming, and then I fixed the VSS signal using a Pulse correction adapter. The VSS from the Getrag is a 2000 ppm square wave generator. Depending on the year of the ECU it is looking for a 4000 ppm Sinewave (ac) for most of the 93 ECUs, and 40 pulse per shaft revolution for some 93 ECU's. Here is a link to a pre-made one (I had to design and make one myself back then)...

http://www.hawksthirdgenparts.com/products/Universal-Speedometer-Signal-Interface.html

hope this helps

[dedgar]

Thanks for the link.
I have made a little progress.
I am currently thinking that the tb butterfly isn't open enough at closed throttle. That being due to the IAC 59 count that Ryan told me about in the scan I sent him. I've open it up a bit and it seems to have liked that. Took the car for a drive and it only died once. Stumbled one other time but overall did rather well.
I'll crack the tb open just a bit more, make sure that the TPS adjustment is where it should be (back probe for voltage). Then take another scan for Ryan to check over.
Just as an OBTW, when I bought the car the owner listed the tb as a N*. When I emailed the builder about the engine, he told me it was an LT-1. Well it definitely is a N*. I don't know what Ryan was told it was when he did the initial chip burn. So I will make sure that bit of info is included.
Another item, I thought the Getrag VSS was 4000ppm.

[robertisaar]

if i were you...... i'd open up the throttle blades so that your IAC minimum values sits near 20 steps. that's roughly what it would be in a factory application.