Have a 86 tpi 305 . Stock chip , 2032 compu cam . Engine rebuilt about 20k ago . I have no codes in the ecm . It ran great up untill last week . I started to backfire out the exhaust every so often , mainly when engine breaking at 2000 rpm . Then it started to back fire under tip in cruise at 2000rpm , low speeds 35 mph and under . Then it got worse , and worse . At presesnt time it backfires all the way through the rpm band , from light load to heavy load . I have lost alot of power . I checked the resistance of my plug wires , found one bad . replaced it no change . I also have a super coil , w/ about 30k on it . I adjusted my min air , and tps . i checked tps voltage through its range . i have it set at .5v and goes upto about 4.5v . I checked my psi its at 45 with no vaccum , but the needle jumps high and low . Its done this since i have owned the car . I think the psi jumping is do to bad check valve on pump , because it loses psi at the fuel rail after the i shut the car off , with return line pinched . I haven't checked timing , and i don't have a tech 1 or 2 ., so no scan tool data . Oh and i pulled the intake off in nov and replaced the gaskets , except for the base i left it on . I don't think its a air leak . Thanks for any help.

 

When it backfires, does the SES light come on?

 

no ses light comes on . I can't tell you for sure it is a electrical or mechanical . I also want to note that i have no emision control devices on my car . That being said , my egr is still on but not connected . Now i do have a slight surge when cruiseing with tip in on gas pedal . But i have never found a malfunctioning egr to back fire . The back is not a very loud back fire , but it has become louder , and louder .

 

Ya, I read your post about no codes being stored, but asked about the SES light on when it backfired (at the same time) because that would indicate a fault within the distributor(module, PU Coil, reluctor, etc) which would not store a code...only indicate that (with the light on) the ignition pulses are not being detected.

That said, now that you mention you "have no emission" control devices, I'd question why you are not setting any codes?

Maybe list in detail what has been removed form the car, than also what you did to compensate.

Cool?

 

No smog pump , just removed , and capped headers , egr just unhooked , and all evap realated componets removed . No codes for any of them . Did nothing special , just removed . Its been like this for about 20k miles . Always ran great , never have had a problem .

 

Since you don't have a scan tool, you may need to do it "the old fashioned way", and remove the plugs, see if one or more cylinders are running too rich.

Assuming the timing is good, and functioning through advance, you could have one or more cylinders (maybe pointing at an injector?) running rich, the unburnt fuel then reignites in the exhaust pipes.

One more thing, no exhaust leaks either?

 

Check the distributor cap- look for cracks, use a spare known good one for testing purposes. Check the ground for your coil.

 

Yeah i could test my injectors with a noid light . Or unplug any to see if i notice a differance . It not the cap or wires , or ground . I have new cap , and button . And i new metal ground strap in the dist . I checked all my wires for resistance . I really need to view some live data .

 

if you are curious , I have checked my timing , which is 10* . I have also pulled my injector wires loose to perform a balance test . I found that #7 cyl had no change when removed . I pulled number #7 plug , and found it completly carboned up ( no gap ). So i performed a compression test . #7 actually have the best at 165 , the rest where at 150-165 . So assuming that plug is good , could have had a crack in it , then the fuel injector has to be leaking . So i pulled my intake off and fuel rail loose . I then pressurized the rail and pinched both fuel lines to hold psi in the rails . No leak . So does anyone think if the injector went bad that it was take to long to close allowing fuel to spray in after spark? Causing the plug to fuel then allowing fuel to enter my hot exhaust and ignite . HMmm........ one more thought anyone know what the resistance of the injector is supposed to be i'm gunno go check that real quick .

 

Oh and 8mike9 good call on the injector , if thats what it is , which i think it almost has to be . I was almost sure it was going to be a burnt valve . But compression is good .

 

""I pulled number #7 plug , and found it completly carboned up ( no gap ).""

Was this the same cylinder you had the bad plug wire on before? If so, this would/could account for the shape the plug was in, not the injector.

Should have tried a new plug first, but now that it's apart, might be a good idea to have the injectors sent for cleaning and balancing.

INjector should read about 16ohms...won't tell you about flow though, only the coils integrity and ability to work.

I/e, you could get good reading, but poor flow

 

No it was not same cyl with bad wire , that was number 8 . Ohms are 64-66 on all cyl . Going to have them balanced and checked thjis week.