Im thinking fuel pump, but here's why: Im getting a bumpy idle and popping/misfiring at WOT before shift. I checked the plugs, gaps were all around 55 I know stock is 50, but thats Not a cause for concern. I just bought this car a couple days back and this is the only mechanical problem. Car has 170k. Acceleration is outstanding otherwise, just a bumpy idle and backfiring WOT shifts. Wires and plugs look to be relatively new, couple years old max and in good condition, and the spark plugs themselves look fine. Opti terminals appear to be corrosion free and in good shape.

On the highway tonight I saw the backfire flicker on the windshields on the cars behind me.

What should I look for while scanning WOT at shift? No SES lights flashed like my 1996 Formula did when it got a misfire, but maybe the obd1 system doesn't do that??

Ill check Fuel pressure at the rail tomorrow.

Does this all sound like a fuel pump issue? The guy I bought it from said he just replaced it. I'll call him tomorrow as well and ask.

 

u check the filter? also what year is this vehicle? Is it acting like its running low on fuel top end? I guess you can try looking at the fuel pressure at WOT.

 

Its a '94. I can't check FP at WOT right now. Ive been reading the archives and alot of people say to check the coil and wire. Well backfiring is when the fuel is hitting the exhaust and popping, so I guess that means there is fuel, no spark. Other than the bumpy idle and WOT shift backfire, power is great. Power cuts out as it's backfiring and I have to let off the gas most of the time for it to shift. But the power is there all the time, no hesitation off the idle, nothing but those 2 spots in the RPMS.

 

Are you hitting fuel cutoff ? 5805 RPM (stock) then cuts back on at 5794 RPM , bucks and pops. Should not happen unless rear was changed or shift points are exceeded w/o changing stock cutoff. Any mods, are you an A4 or M6

 

Automatic. Actually I wondered that before I posted but brushed it off. I believe the ECM is stock, but I do have 315/35r17s out back, normally only .o1% faster. However, they are Sumitomos which run much narrower and smaller than a real 315. When I pass one of those speed indicators, it says Im going faster 2-3mph faster than I am. That could be an issue too. It is getting very close to that when it happens. If I left off the gas before that range, it will get to the next gear no problem no backfires.

 

I had the exact same problem i ran codes and my opti-spark came up. It had moisture in it from a recent heater hose blow out, so if any fluids of any kind that are leaking directly above your distributor it will cause backfiring and miss hop at idle. (Or you could need a new distibutor)

 

Well wouldn't a code for the opti pop up? The SES light works, but no codes have ever flashed up.

And also the computer has a wacky tune in it. We pulled the BIN last night. We think my problems might be related to the speedo/rpm shift points.

Here's mine in the car now:

Speedo Scaler - 517
scaler fraction - 4.38
scaler scan tool - 43.82
scaler pulses - 1.53

Versus what it should be:

Speedo Scaler - 26
Scaler Fraction - 1.01
Scaler scan tool - 43.8
Scaler Pulses - 34.256

Gears have been verified to be 3.23s.

 

well yea but i would checkl it out man those opti's tend to go out alot lol but if i were you start eliminating small things

 

ok im new to the forum thing how do i post anyone. cause i need to post how to get to the dam spark plugs i cantr get to them if my life depended on it any easiest ways to get to them

 

how many miles are on the car? You can do yourself a big favor and check signal coming out the opti to make sure all are firing. If you have less then 90k on stock plugs I would say its not your plugs. If there was water inside the cap causing grounding you would not get an opti code as the computer has no imputes at the cap and rotor part of the opti it simply distributes the signal from the coil at this point.(you should only get codes for the optical side) anyone chime in if I'm wrong.

And regardless of speed, the trans is spinning at x and the rpms are x. The only time it hits the limits are at X. So if your rpm limiter was set to 4k it would then cut off fuel at that point regardless of MPH. Same for the speed limiter, it will only cut out when the pcm thinks its at the limit... and for ZR tires from factory I believe its set to over well above the capabilities of the car. Does this make sense?

 

170k. Top end was rebuilt less than a year ago, supposedly. Plugs and wires look less than that and in good shape. As far as I can tell.

Is there a opti sensor check in Tuner Pro?

 

In the lower left corner, under the last post is a button labled "NEW THREAD". Same location, under the last "topic" when looking at a forum topic listing screen.

 

New coil and wire solved the problem. The wire was rusted at the coil connection and wasn't even contacting. The coil terminal had some white corrosion on it. Im just glad the trans and opti are fine.