Couple second delay in deceleration; a common problem???

fairlane292 · Mar 5, 2024

I am in the early stages of a full body off frame resto of a 1969 Datsun roadster. I will be using a 5.0, T5. 8.8 rearend in the build. Due to tight clearances in the engine bay I've been thinking the more compact 94-95 5.0 would be a better choice than the Foxbody 5.0. I recently was communicating with a local shop that does a lot with Fox and SN mustangs and the owner mentioned that the sn 5.0s have a short delay when decelerating and further that there is no fix for this. I had not seen anything on the web about this but surely folks out here would have exposure and info about this if it "is a thing". I would really appreciate any info that members here can provide about this symptom. Thanks so much! Jim

shovel · Mar 5, 2024

I'm guessing that's like the high idle thing that a lot of people struggle with when trying to work with a stock ECU and a 30 year old Mustang with various minor mods.

My opinion is it's just not worth trying to work with the stock ECU anymore, we used to not have a choice and then later with stuff like the quarterhorse (RIP) it was nice to have some more control.
But now the low hanging fruit is just go to speed density on a ms3 with widebands.. that modernizes engine control and as far as I can tell those little quirks vanish. It's a bit more money up front but I think in the long run it's a whole lot lower cost.

Obviously that only works on cars/locations where emissions testing permits it.. in your case with a 69 Datsun that's not likely a concern.

fairlane292 · Mar 5, 2024

shovel said:
I'm guessing that's like the high idle thing that a lot of people struggle with when trying to work with a stock ECU and a 30 year old Mustang with various minor mods.

My opinion is it's just not worth trying to work with the stock ECU anymore, we used to not have a choice and then later with stuff like the quarterhorse (RIP) it was nice to have some more control.
But now the low hanging fruit is just go to speed density on a ms3 with widebands.. that modernizes engine control and as far as I can tell those little quirks vanish. It's a bit more money up front but I think in the long run it's a whole lot lower cost.

Obviously that only works on cars/locations where emissions testing permits it.. in your case with a 69 Datsun that's not likely a concern.

Intersting... I plan to keep the 5.0 in stock form exc maybe street aluminum heads. Is this high idle deceleration something that is not generally seen in stock configuartion? Thanks so much for your input. Jim

Daryl · Mar 6, 2024

What about doing away with the stock FI and go with either an intake/carburetor combo or a Snioer EFI unit. That’d rid the “delay” altogether

ttocs · Mar 6, 2024

what kind of motors is that guys use to? Never heard this myself but there are a lot of cars I have not driven.

92wastheyear · Mar 7, 2024

I have had couple stock Datsun Roadsters (1600's) in the past. Both of them were '67s with the short windshields and all the toggle switches. I traded the last one in for 69 Firebird Convertible when I starting having kids. I sold that when the economy went to shit in the early 2010s. Once the kids grew up and moved out, I picked up my current '96 Mustang convertible. (Still needed a backseat for the dog)