Detonation at high rpms...

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Silent Assassin

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Well, my Mark has been acting up ever since I bought it several months ago and I have not been able to figure out the cause. Car is a 1994 with 178K miles. Whenever I take the engine above 3800 rpms, the engine starts popping, like its detonating or misfiring and lose power and have to let off the throttle. Sometime at low rpms, the car also has a bit of hesitation, comes and goes. The CEL is not being triggered so I have no idea what the problem could be. Weird thing is that it does not do this every single time, sometimes it'll pull strong all the way to 6K, gets me all thingly, then on the next WOT run; snap, crackle, and pop, it runs like crap. :mad:

This is the rundown of the things I've replaced/added to the car so far.

-'98 tranny w/ jmod (OEM tranny was shot)
-Removed intake silencer added a drop in K&N filter.
-160 themostat
-Trickflow UD pulley
-removed the 3rd cat and silencer added a 2 in 2 out Magnaflow muff.
-Motorcraft copper plugs gapped at .054
-Walboro 255 fuel pump
-new fuel filter

I think thats about it.


Any ideas guys? Thanks in advance. :)
 
check fuel pressure. my cougar would do that. turns out every once in awhile the in tank sock filter would fold up and cut off fuel flow. took me forever to find it. but it had the effect you described. sometimes perfect, sometimes not (backfired, no power etc.), and very intermittent.
 
Sapperfire said:
Can you link up a vid on YouTube?
Click to expand...

I'll do some WOT runs tonight, in a closed course in Mexico...

I'll upload the vids to youtube and post them up here.


chris2523 said:
check fuel pressure. my cougar would do that. turns out every once in awhile the in tank sock filter would fold up and cut off fuel flow. took me forever to find it. but it had the effect you described. sometimes perfect, sometimes not (backfired, no power etc.), and very intermittent.
Click to expand...

Does sound very similar to your problem. I would've never thought about checking the sock filter. I'll check the fuel pressure see if for some reason the engine is not getting enough fuel. I did put a new sock filter when I installed the Walboro fuel pump, damn I hope I don't have to drop the tank again. :( Maybe the fuel pressure regulator is bad?


NoLimit95 said:
How was the 98 trans swap done, re-pin or electrical part swap?
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Re-pining. I did a ton of reseach before attacking the job, thank you search button. ;) Transmission was from a trade-in clunker 1998 Grand Marquis with 70K miles. Tranny is working great and feels great with the jmod.


slowmkviii said:
Check for codes anyway
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Hmmm, I tought if the CEL was not triggered, the car was not throwing malfunctioning codes. I'll check for that today, hopefully something comes up that will shine a light on the problem.


Thanks for the insight guys. :)
 
have u replaced plugs and wires......... my 95 bird 4.6 would eat wires like crazy right at the boot and arc out sometimes wen it completly warmed up itll run great but other than that nothing.........it was so intermitent it pissed me off so i went and got one more set of wires and 4 rolls of electrical tape and taped all of them from the boot all the way to the pack and it worked fine after that........ not saying thats ur case but try it first its simple and inexpensive 60 bucks for wires a good set not top of the line but itll put you in a spot to see if thats the prob or not
 
1sik32v said:
have u replaced plugs and wires......... my 95 bird 4.6 would eat wires like crazy right at the boot and arc out sometimes wen it completly warmed up itll run great but other than that nothing.........it was so intermitent it pissed me off so i went and got one more set of wires and 4 rolls of electrical tape and taped all of them from the boot all the way to the pack and it worked fine after that........ not saying thats ur case but try it first its simple and inexpensive 60 bucks for wires a good set not top of the line but itll put you in a spot to see if thats the prob or not
Click to expand...

sorry i didnt completly read ur post but it says only pugs not wires so try that if u havent
 
unity said:
What fuel are you using? Octane and brand please.
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Premium 93 Octane, Exxon brand. I'ved never ran the 87 or 89 stuff since Premium is recomended for these cars. Might try out Shell, see how it responds to that. I have no idea what the previous owner ran for 175K miles though. Something tells me he probably ran the cheapest gasoline in town...


btw, I was informed by the previous owner that he changed the ign. coils for some "Duralast" from Vatozone. Epic Fail. Maybe one has gone bad? :confused:


btw x2, the stig made several runs last night in my car on a secluded, pedestrian free road course outside city limits in Mexico. I'm in school right now, but I'll upload the vids later tonight. You will totally notice the popping sound on the first run.
 
I'm surprised none of you guys know the fix for this problem.

I mean, seriously! I thought you guys were car guys!


The fix for detonation at high RPMs is simple. Don't rev the motor to "high" RPM's. :lol:


Sorry, just postwhoring.
 
My first Mark did that and threw a cell for lean cylinders. I ran a good injector cleaner in a tank of gas and it fixed it believe it or not :confused:
 
Update: Link to video now posted. Sorry for the delay, the weather has been pretty severe.

.

Notice how on the first run, it pops maniacally above 4K rpms, and I have to let off the accelerator. :( On the third run, it pops once right at 3500 rpms, then over 4K it just goes wild and I let off again.

Second and 4th run: no pops.

edit: When I say "I", I actually mean "the stig".

2002WRXSTi said:
My first Mark did that and threw a cell for lean cylinders. I ran a good injector cleaner in a tank of gas and it fixed it believe it or not :confused:
Click to expand...

I here ya, so, I went out and bought a bottle of concentrated "Gumout" fuel system cleaner and dumped it into the tank before the "fil-er-up" earlier today. Thanks for the insight man. :)


07194890102_220x220_a.jpg




btw, I also picked up a W3Z2 ECC IV PCM today off a '93 Mark at a friendly neighborhood salvage yard. I almost got my hands on its drive shaft, but since its a "self serve" auto parts yard and I didn't take the proper tools to takle the job, I'll be hitting the salvage yard again next week. Counter guy said I could have the shaft for $35. :eek: Car is a Light Moca 10/92 built Mark.

I'll be installing the PCM tonight.
 
The GPM on your fuel pump may may not hold the pressure under high load demands like 80+ MPH.

I had a similar issue when I was in college and the guy said they just put in a new fuel pump and that could not be the problem. He got it from Advance and it was NFG.

You may have a similar issue with fuel delivery: Suction strainer, electric connections dropping voltage, restricted fuel filter or the pump may be under rated. To me, it sounds like you are running out of fuel at high RPMs. Alcohol in gas will also lead to corrosion and injector wear.

I am no expert with engine controls but the O2 can tell you if it is lean.
 
I agree with dollman0 after hearing it. I hear more of a miss than anything. I did not read the whole thread again, but have you gotten fuel pressure readings at high RPM?
 
I've never heard anything good about aftermarket coil packs, especially duralast ones.:)

When you go to get that driveshaft, I'd buy the coil packs off that car too, just to try them out.

I've been driving gen 1's for years now, and have never had to change a coil pack.
 
billcu said:
I've been driving gen 1's for years now, and have never had to change a coil pack.
Click to expand...
One thing I noticed on my Gen1 was when I replaced the wires I didn't swap over the corrugated plastic covering to the new wires. Turned out to be a mistake as the wires chafed enough that they would crossfire on a rainy day.

I did have a bad misfire on my Gen2 because of oil seeping up the boot. I got a coil from AZ and a 2 spare boots from Pep Boys. Put in the coil boot and has been fine so far. However it seems to be very rough one 21 degree day start up. Like it was missing cylinders until I got some heat into the engine. Been to lazy to pull all the boots to check for any more oil :confused:
 
dollman0 said:
The GPM on your fuel pump may may not hold the pressure under high load demands like 80+ MPH.

I had a similar issue when I was in college and the guy said they just put in a new fuel pump and that could not be the problem. He got it from Advance and it was NFG.

You may have a similar issue with fuel delivery: Suction strainer, electric connections dropping voltage, restricted fuel filter or the pump may be under rated. To me, it sounds like you are running out of fuel at high RPMs. Alcohol in gas will also lead to corrosion and injector wear.

I am no expert with engine controls but the O2 can tell you if it is lean.
Click to expand...


I feel like the engine is running out of fuel as well. I got a high pressure 255LPH Walboro along with a new fuel filter, but like you said, the connections may be causing the problem, or maybe a twisted fuel line, or the suction strainer. I need to check for all of that.

Quick note: when I installed the fuel pump, and removed the fuel pump relay to the release the pressure from the fuel line, the pump would still turn on? :confused: The car never turned off even with the relay removed, so I just went ahead and removed the pump anyway, but there was hardly any pressure on the line.

I'll gonna be performing the paperclip diagnostics test tomorrow, see what turns up.

unity said:
I agree with dollman0 after hearing it. I hear more of a miss than anything. I did not read the whole thread again, but have you gotten fuel pressure readings at high RPM?
Click to expand...


Nop, but I'm gonna be taking the car to a mechanic to check for that later this week if the symptom persists. More than likely its cheaper to get the fuel pressure checked with a local mechanic than buying the guage, and I really need to get that fuel pressure measured, make sure I'm getting enough fuel.


billcu said:
I've never heard anything good about aftermarket coil packs, especially duralast ones.:)

When you go to get that driveshaft, I'd buy the coil packs off that car too, just to try them out.

I've been driving gen 1's for years now, and have never had to change a coil pack.
Click to expand...


I'll be heading to the salvage yard on Wednesday to pick up the driveshaft and I'm gonna snatch those coils as well. One of the Vatozone coils seems to be making a ticking sound, quite noticable when I touch the spark plug wires. The ticking feeling is more eminent on two of the wires. :confused: I might go ahead and grab the '93's fuel pressure regulator as well just in case mine is bad.

2002WRXSTi said:
One thing I noticed on my Gen1 was when I replaced the wires I didn't swap over the corrugated plastic covering to the new wires. Turned out to be a mistake as the wires chafed enough that they would crossfire on a rainy day.

I did have a bad misfire on my Gen2 because of oil seeping up the boot. I got a coil from AZ and a 2 spare boots from Pep Boys. Put in the coil boot and has been fine so far. However it seems to be very rough one 21 degree day start up. Like it was missing cylinders until I got some heat into the engine. Been to lazy to pull all the boots to check for any more oil :confused:
Click to expand...


Hmmm, interesting. I'm gonna be getting some FRPP wires once the money start flowing again. Damn my depleted fundings!!! :mad:



Thanks for the help guys, I'll keep you updated on the problem. :)
 
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