Hesitation at WOT; Backfiring, TFI Module? Tried everything!!

ozanracing · Apr 27, 2007

Well I'm having this problem where under load (wot) the motor is breaking up. Very noticable power loss, popping, backfiring noises....It all started when I was Trying to get the idle just right. Now, it's also hanging at 2500rpms, then dropping down to normal (feels almost like an injector is sticking open??). I pulled the IAC motor plug, set the idle, and then disconnected the battery and let it sit over night. In the morning I fired it up and started driving, then connected the IAC motor. Then the problems started.
I tried lowering the fuel pressure to a low of 35psi vac disconnected. Seemed to like 37psi. Im using 30lb injectors, and a vortech (C&L) maf with adjustable sample tubes. I've tried clocking it many different ways and it seemed to help/lessen the wot problem. But then I thought is the MAF ignored by the computer at WOT? If so, that would be eliminated... The weather has been extra warm out and I thought maybe it's detonation, so I reduced the base timing from 16*BTDC to 14*BTDC. Didn't help. It's also running hotter than normal, 210*or so... I have a 180* thermo/electric fan and it's always run right at 180-185*...Does this sound like a bad TFI? At first it seemed intermitant, but now it's happening every time i step on it. Under 3000RPMS it's fine mostly...For all I know it's the original TFI unit, I never replaced it before. It's only $40 from Autozone of $45 for an Accell piece....ANY IDEAS??? It was running so very nice, linear smooth power up to 6000rpm, but now I'm hesitant to drive it, let alone enjoy the engine Any suggestions are appreciated!

PS.
The other concurent/related problem is that at steady throttle, the motor will occasionaly 'stumble' and cut out momentaraly. Seems like this could be due to the crappy MAF transfer? I was thinking of getting a granetelli MAF....

jrichker · Apr 27, 2007

Dump the codes and see what the computer says is wrong…Codes may be present in the computer even if the Check Engine light isn’t on.

Here's the link to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great.

See http://www.troublecodes.net/Ford/
OR
See http://www.mustangworks.com/articles/electronics/eec-iv_codes.html

IF your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.

Codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

For those who are intimidated by all the wires & connections, see http://www.actron.com/product_detail.php?pid=16153 for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Wal-Mart.

Or for a nicer scanner see http://www.midwayautosupply.com/pc-7208-90-equus-digital-ford-code-reader-3145.aspx – It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $30.

stang8urimport · Apr 28, 2007

A misfire/backfire under load sounds more like a weak coil. The TFI works, or it doesn't. Ususally if the TFI goes bad, it overheats (the TFI Module) and the car dies., then after a full cool down, it might start back up again.

blownLX5oh · Apr 28, 2007

After trying the above mentioned ideas...look HARD at the C&L MAF. Never had any luck from their meters. I had an LX with a Vortech and had almost the same condition(s) you're describing....chased it back to the MAF.

For the LONGEST time I thought mine was in the timing/fuel. It was leaning the engine out @ WOT.....also, the temp shot up to WICKED hot and the headers glowed.....

I borrowed a meter from a friend (same calibration) and the car ran like a different animal.

I highly suggest you borrow a meter like I did from someone with the same calibration (PRO-M if available) and try that.....I think you'll be surprised

Good luck!

I'd like to hear the end result if you'd PM me about it ;-)

RoadKill96 · Apr 29, 2007

Change the TFI mine was doing the same thing but mine was cracked changed it and i had no more probs and change the ACT sensor <--- air charger temp sensor

DmnStr8 · Apr 29, 2007

PoopDawg said:
A misfire/backfire under load sounds more like a weak coil. The TFI works, or it doesn't. Ususally if the TFI goes bad, it overheats (the TFI Module) and the car dies., then after a full cool down, it might start back up again.

Not always. When my TFI went, my car did not die. It would buck, backfire through the intake and the exhaust and would only stall after doing this for bout 30 secs.

Daggar · Apr 29, 2007

PoopDawg knows his stuff but in this instance I have to agree with the others...

I've had some TFI modules do some stupid crap that you'd never think a TFI could do. It's also a cheap swap.

Aliate X · Apr 29, 2007

Something is wrong with your MAF, gaurenteed. I went through the same exact problems.

iwashmycar · Apr 29, 2007

where's the TFI? on the firewall right behind the intake?

ALMOSTFINISHED · Apr 29, 2007

Just a thought, how old are the plug wires? They can do some tricky things when they get old and it may just be a coincidence that it started near the same time you started to tinker. And for $40 bucks even if they don't fix the problem you still have new plug wires. I had a pretty bad stumble and it ended up being the plug boot arching on the header. I had the hood open at night in the dark and had my father rev the car a few times and you could see the spark from the boot to the header. Either way good luck with everything and post up what the problem was once you find it.

Nick

Daggar · Apr 29, 2007

iwashmycar said:
where's the TFI? on the firewall right behind the intake?

Attached to the bottom of the dizzy.

ARMAGEDON · Apr 29, 2007

Sounds like what my '94 was doing. Replace the distributor. It sounds like the magnetic pickup is going out.

getusummm · Apr 29, 2007

I would say trouble shoot it properly before just throwing a bunch of parts at it like has been mentioned. Pull the codes and then go from there. Do you have a fuel pressure gauge? When is the last time you put a set of plugs in? When is the last time you changed the cap and rotor? There are alot of little things that you should look at, especcialy if it has been a while since a major tuneup. Good luck

stang8urimport · Apr 30, 2007

Daggar said:
PoopDawg knows his stuff but in this instance I have to agree with the others...

I've had some TFI modules do some stupid crap that you'd never think a TFI could do. It's also a cheap swap.

Agreed. Most of the time they fail the way I said, but sometimes they do spit and sputter before taking a poop.

ozanracing · Apr 30, 2007

Hey guys.

So here's an update. I bought a new TFI module from kragen. Put it on and it did not fix the problem. Althouygh it did seem to smoothe out the part throttle cruise, there are still some 'hicups' while cruising.

I unplugged my MSD box, to see if that was malfunctioning, and since this had happened before and was a bad MAD box. That wasn't it.

I ordered a 75mm PMAS MAF to see if that'll do it. I don't feel bad buying these parts, since I know it's best to just get them on the car asap. (MY current MAF sucked from day #1) So that's coming withen a few days.

The magnetic pickup is something I was worried about, though I don't have another dizzy to swap out and test.

I have played with the FP, yes I have a gauge, brand new MSD cap/rotor, OLD wires 2+ years, So I'll get some new ones, but new plugs that are in good shape (less than 1000 miles)

Got one suspecious vaccume line that's gonna get replaced, but that's not causing the WOT problems.

So I'm just hoping the MAF will be the fix-all I need. I popped the valve covers, no bent valves.....Thought MAYBE one of my VENOM injectors could be sticking open??? Seems like that might cause similar problems to what I am experiancing....

Weak coil maybe??? Worth getting a new one???

Summery: Tried new TFI, no-go. Now waiting for new properly calibrated MAF and some new plug wires. Will update when parts arrive.
Let me know if you guys have any more Ideas!

ozanracing · Apr 30, 2007

Thanks everyone!

HISSIN50 · Apr 30, 2007

If not mentioned and you have an extra (so as to keep parts tossing to a minimum), if you have a spare coil, I'd try it out. I might also consider running with the box disconnected and see how it does (for diagnostics only).

Good luck.

EDIT: I think I missed your post two-up earlier (possible timing overlap).

jrichker · Apr 30, 2007

What was the result of dumping the codes?

ozanracing · May 1, 2007

Damnit.

After doing more research, I've definitivly ruled out the maf from WOT misfire/backfire/hesitation
etc. The EEC IV reverts back to pre-programmed spark and fuel tables and ignores the MAF
at full throttle. On later 94-95 cars with EEC- V the MAF IS refrenced at WOT....So>>> I'm now thinking
ignition crossfire? (spark plug cables could be damnaged and now have too much resistance??
But for this to just *BAM!* happen one day when I turn the car on makes me think....it's
not the wires....I'm going to check
the primary/secondary restince on the coil and see if they are withen spec....Maybe the coil went bad???

Okay, so rewind back to 2 weeks ago....Car was driving proper....One day the motor just shut off
(see this thread...) anyway a connector had come undone on the fuel pump in the tank.
I fixed it and everything was fine...For about a week. (could this be related?) SO then I was trying to get the idle
speed/quality fine tuned. I decided to unplug the ISC motor and set the idle to 900rpm.
Then I unhooked the battery and let the car sit overnight. In the morning I started it
up and forgot to plug in the ISC connector. I drove it for a block or 2 and noticed the idle
was hanging up at 2500rpm. I remembered the connector and plugged it back in with the engine
still running. EVER since then the performance has deterioited to the point where I dont
want to start it untill I get the new MAF to try. But what the **&^% I don't think this is going to fix
the car.

SO>> What now? How can I test the magnetic pickup in the dizzy? If the maf dosn't fix it, and the
magnetic pickup/coil/new wires also dosn't fix it....Fuel? I don't have a FP gauge in the cowel, only
mounted on the fuel rail. So I cant tell if there's a pressure drop/spike going on at WOT....hmmmmm....

Anything else? Should I do a compression test? I dont have the adapter for my gauge, but it's prob. cheap...
Let me know if any other ideas come up....

ozanracing · May 1, 2007

jrichker said:
What was the result of dumping the codes?

You know actually I've never pulled codes ever after 2 years of serious mods, and everythinhg always went smooth.....

Hesitation at WOT; Backfiring, TFI Module? Tried everything!!

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