Rough idle / stalling (was - Bad spark plug wires?)

[kris812]

So question.. what port is it that you have blocked off? Evap system? That's about the only thing I could defeat on mine, and it's crossed my mind..

0.5 MAF reading on throttle punches is normal.. 1.2 is WOT "loaded".. ie on freeway and peg the throttle..

But hey glad you got it fixed and was something easy!

 

[terryjm1]

On some GEMs 4.0s the evap port is on the right side on the upper plenum. That is the one I capped. I believe I combined a non-AEL and AEL plenum / inlet manifold assembly. I didn’t realize that during assembly. I was just picking the best stuff from the hoard. I think the bottom is non-AEL and the top is AEL. I have a couple totes of that stuff. I suppose I could correct it but it works fine. It seems every D1 purchased comes with a tote of spare engine bay stuff. Upper plenums seem to be quite popular to hold onto when replacing an engine as well as alternators and starters. I really should just take them to the metal recycler. I actually got close to loading my trailer with my expanding scrap metal pile today but decided to wait until my 13 yo could join me, He really likes going to the metal recycler. It’s kind of like golng to Sanford and Son. There is a lot of cool junk to look at and I give him half the cash. My dearly departed great uncle was a sort of old white guy version of Fred Sanford. I really liked digging through his yard full of junk. I totally get my son enjoying the experience.

Frankly. it seems odd to run that evap line all the way to the driver side but that is how mine is set up.

 

[terryjm1]

I want to correct myself as I certainly don’t want to share false information. The intake / plenum combinations from D1 to D1 are different and I did mix and match but I really don’t know that AEL or non-AEL is the difference maker. To further complicate things, the two engines picture are not the original engines in the cars. The first picture show,s, in this D1 the port being used but in the one I had issue with it is capped. My 96s, one automatic and the other with R380 are non-AEL but have different plenum ports. The 2nd and 3rd are a 98 with AEL. The last one is the same D1 as the first photo that shows no port on the upper intake.

 

[DiscoClay]

I run into vapor lock in the fuel rails after driving on the freeway for a while (~45m to a few hours). This causes rough start, choppy idle, and stumbly low rpm throttle response.. If I let it idle for about 30 seconds it seems enough hot fuel (and vapor) makes it out through the regulator and enough (cool) fuel works it's way into the rails to eliminate the problem. I think heat sink on the rails would solve the problem.. and likely boosting the pressure up from ~32psi to ~45psi would probably solve it as well.

Note: the injectors on the 14cux (94-95 NAS) are rated at 19lbs@45psi... so I am guessing the cux can handle mapping with the extra pressure.

 

[AlWorms]

That sounds a lot more like leaky injectors, causing a rich mixture on hot starts - I had that on my 97 3.9 (japan) until I replaced my injectors.

If I didn't let it idle for a bit, or hold the revs up to about 1200 for a while as an alternative, it would stall upon selecting drive, hunt and hesitate on acceleration.

The original injectors are a disc type and have a sorter life, but are rebuildable. I chose to fit Bosch 4 hole injectors instead.

 

[DiscoClay]

That sounds a lot more like leaky injectors, causing a rich mixture on hot starts - I had that on my 97 3.9 (japan) until I replaced my injectors.

If I didn't let it idle for a bit, or hold the revs up to about 1200 for a while as an alternative, it would stall upon selecting drive, hunt and hesitate on acceleration.

The original injectors are a disc type and have a sorter life, but are rebuildable. I chose to fit Bosch 4 hole injectors instead.

I have the 4-hole injectors as well. And they've been replaced. Also, the pressure is low [imo].. at around 28psi when all warmed up. I need to install an adjustable regulator [or calibrate me existing one with some crush].

My buddy down in the desert started seeing the same problem: he figured he'd experiment with the vaporlock idea and so he sprayed water on the fuel rail... this instantly resolved the problem.

Its vapor lock.

*i have experienced leaky injectors as well as stuck injectors [*not fun*] and this does not act like that. It acts very much like there's "air in the line" [vapor in the rail].

 

[special ed]

Robertf’s GEMs app allows you to pair the ECU with the 10AS. This was the first time I used it for that and it worked perfectly.

last i heard the app was not working anymore. Did that get resolved?

 

[terryjm1]

last i heard the app was not working anymore. Did that get resolved?

I downloaded it a long time ago. It worked fine for me.