Backfire after deceleration

[smagnotta]

I have a small backfire after deceleration, when shifting between gears and going from a higher RPM to a lower RPM. Anything I can check or a suggestion?

Thanks

 

[turboa7mgte]

we need to know more.... What Mods do you have? aftermarket BOV? that would cause some of your problems..... You could be running Rich..... without knowing what you have we are just guessing.

 

[DrakeMK3]

Agreed. We must know more information like, are you running a cat? No cat, aftermarket bov, bad plugs, etc....the list goes on and on. Give us more info.

 

[gixxer750]

my car backfires on deceleration..... but thats open DP....

 

[smagnotta]

Please see other thread "Stalling after high RPMs" - it is related - thanks

Mods:

Lexus AFM
550 cc injectors
HKS SSQV BOV
racing intercooler with custom pipes
suprasport turbo elbow, 3 inch downpipe, 3 inch exhaust, tanabe cat back
1 super flow CAT
(Stock Turbo)
SAFC
HKS EVC electronic boost controller
Zeitronix Wideband O2 sensor (just the lambda and the air/fuel ratio are hooked up)

I used the wideband. I just got it and installed it. It's working and I adjusted the air/fuel ratio with my SAFC. I was running rich. Not pig rich but it needed tuning. It helped a little bit but the car still has the following problems:

(1) misses at idle
(2) backfires when decelerating
(3) stalls after high RPMs

I don't think the missing at idle is due to richness because I checked the Vf voltage and it says 2.5 and the air/fuel ratio is at 14.6 and 14.7 with the wideband.

I have replaced the spark plugs twice as these problems have been occurring for a while, the plug wires and one coil pack. Even the ground to the coil packs. These were things that needed changed but it did not affect anything.

I found that replacing the stock O2 sensor helped some with the backfire problem. It was the original one with 122,000 miles on the car and was ready to be changed.

I have the S-AFC at -20% and -23% at most of the higher RPM levels.

I am getting 23 miles per gallon and I drive it both in the city and the highway.

I replaced a lot of things on this car. Here is a partial list of parts I have not replaced or have not done:

1- TPS -Throttle position sensor
2- CPS -CAM position sensor
3- Check or reset the timing
4- ECU - the main computer
5- 2 original coil packs.

Thanks,
Sal
'87 T

 

[turboa7mgte]

Ok thats better.....

Lets start with the easy one, stalling after high RPM's: This is most likely from you BOV venting into the atmosphire. I would say tighten the screw down until you can get the car to Idle after higher r's. If you have the SAFCII you can mess with the dec/air settings.

Missing at Idle: I am guessing you have Denso Injectors..... I have had problems with mine. if not then try adding some fuel at 1000 rpms on the low throttle setting on your SAFC. If that dont work then check your timing. and make sure your plugs are gapped correctly. and check all of your grounds and I meen all of them.

I think the problem with the backfiring would be when your computer changes the map from closed to open loop. your SAFC is taking care of map for the most part at WOT, then when you let of the throttle the ECU takes back the map and is kinda confused at this point..... its kinda of a raw way to explain it but its all i got....
Mine would back fire quite often and I am thinking that there is just some leftover fuel in the cylinder and it has to go somewhere so BOOM!! out it goes. I watched some fast ass supras do the same thing and they tell me that its tuned rich for the street.

I wish you luck and i hope this helped you a little at least!!!

 

[turboa7mgte]

I see that you are venting the bov back into the intake from the other post you wrote.... So disregard my fix on that.... I would say take apart the ISC and clean it... you should be fine.

 

[smagnotta]

I think the problem with the backfiring would be when your computer changes the map from closed to open loop. your SAFC is taking care of map for the most part at WOT, then when you let of the throttle the ECU takes back the map and is kinda confused at this point..... its kinda of a raw way to explain it but its all i got....
Mine would back fire quite often and I am thinking that there is just some leftover fuel in the cylinder and it has to go somewhere so BOOM!! out it goes. I watched some fast ass supras do the same thing and they tell me that its tuned rich for the street.

So then I should not worry about this one then?

 

[bluemax]

I've got a similar problem (if you call it a problem). Its only a problem when you pass a cop and the car back fires.

I think my problem is with the catback/down pipe.
My car was converted NA-T.
In the process I changed the catback to an HKS w/ 85mm pipes and HKS 75mm down pipe.
All the electronics are stock-T with bosch plat. plugs. The AFM and TPS were replaced.

 

[smagnotta]

I think this is a common problem. The TSRM says it is ignition timing.

I guess we don't worry about it if your timing is OK.