Engine Bucking While In Gear.

[2011rustang5o]

Ok I had another thread about a good cam for a 331 fox. So I'm starting this separately for this specific issue.
The car bucks around 1600-1800rpm while in any gear under part throttle.
331 stroker ~10.5:1 compression. Track heat 185cc heads, track head upper and lower intake, 70mm throttle body, 70mm maf, blue injectors (donno their actual size), msd coil, Cai with big filter in engine bay (new in the fender kit in the way), BBK long tubes, o/r H and dumped flowmasters, unknown cam specs but it's lopy, stock rebuilt t5 and 3.73 gears. Car was tuned back in 2006 for this setup.

I have put on new o2 sensors, IAC, set tps, new plugs gapped at 50, new cap and rotor, new wires, verified base timing at 10, cleaned maf, checked for vacuum leaks, set idle properly, replaced fuel filter, replaced speedo gears and speedo cable and verified there are no engine codes.

Car ran worse before all of this and all I have done has made it idle and drive light years better. But still bucks.

I think it's a poorly picked cam but is there something I'm missing?


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[90sickfox]

Is it tuned ? Could be a tune related issue.

 

[jrichker]

Do the diagnostic work and let us know what you turn up...

Dump codes sticky

Look at the top of the 5.0 Tech forum where the sticky threads are posted. One of them is how to dump the computer codes. Codes may be present even if the CEL (Check Engine Light) isn’t on. You don’t need a code reader or scanner – all you need is a paper clip, or if your lady friend has a hair pin, that will do the job.
I highly suggest that you read it and follow the instructions to dump the codes. http://www.stangnet.com/mustang-forums/threads/how-to-pull-codes-from-eec4.889006/

 

[Moosee1955]

How bout something as simple as corrosion on coil/ cap. Are your spark plug wires new. A bad or intermittent coil can cause a miss. I know the other reader said use a paper clip but be careful if you slip at all you can burn out a tfi module. Also run a fuel pressure test, pull vacuum hose to fuel regulator, make sure it's not leaking or misbehaving. Bucking usually is electrical, but I'd test fuel as well 1000 to 1800 is where most misses show up, I'm betting on electrical. Measure ignition coil primary and secondary. Measure all spark plug wires. It just takes one thing to act up. One last thing make sure battery is up to snuff, cables clean and tight. Grounds good and tight. Let us know what you find.


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[2011rustang5o]

Oh yea I forgot, it was tuned in 2006.

Already stated I checked codes and it's a new cap and rotor with new wires and plugs.


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[2011rustang5o]

How bout something as simple as corrosion on coil/ cap. Are your spark plug wires new. A bad or intermittent coil can cause a miss. I know the other reader said use a paper clip but be careful if you slip at all you can burn out a tfi module. Also run a fuel pressure test, pull vacuum hose to fuel regulator, make sure it's not leaking or misbehaving. Bucking usually is electrical, but I'd test fuel as well 1000 to 1800 is where most misses show up, I'm betting on electrical. Measure ignition coil primary and secondary. Measure all spark plug wires. It just takes one thing to act up. One last thing make sure battery is up to snuff, cables clean and tight. Grounds good and tight. Let us know what you find.


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I'm a pretty experience mechanic, however what do you mean measure the plug wires? They are brand new. Also on the ignition coil (msd) primary and secondary should I be looking for 12v or higher? Thanks.


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[Moosee1955]

First off you've got a stroked 5.0 95 or older engine right? Even though you've got new wires 8 of them. One could have gotten burned on Exaust. Use an ohm meter, put lead into each end of wire to make sure one wire is not real high or no reading. That parts rare on new wires but could happen. The same thing with coil, your measuring resistance ohms, not voltage. Primary side is between positive and negative terminals. Most good coils 1.3 to 3.0 ohms reading. Real high or no reading or leaking, black ooze replace coil. Secondary reading one lead inside tower where spark plug wire goes, second lead to positive lead on coil. Normal 8 to 12 ohms. Again if reading real high or no reading replace coil. Their is also a running test online if you want to do that. Do the ohms test first. Works for me most of the time. If you or a buddy had a spare coil to try, that's a cheating way, but then your sure. Theirs a lot if crap made in China msd and others that fail or misfire


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[Moosee1955]

I just measured a brand new 3 foot long spark plug wire, that was for my 89 5.0 .probe from meter in each end reading is 10.6 ohms. The longer the wire the higher the reading. If this wire was bad my reading would be 0 or super high like 300 ohms or higher. Inspect the outside of each of yours wires, look for burn marks or anything weird. I like to be thorough when I'm trying to fix a problem, with least money spent. Let us know what you find. One last thing if you have access to a scanner that reads kilovolts reading of each plug wire, it will tell you what cylinder is misfiring. In my day, I'm old! We used a big sun brand scope that showed all eight cylinders firing spikes. I think snap on has a small version In their scanners.


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[2011rustang5o]

Cool il do those test. And yes it's a 93 lx coupe. Could the TFI or PPI cause this too?


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[2011rustang5o]

Well I get wonky readings when I giggle the positive post of the coil. So tomorrow il get a coil and see if it helps out.


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[89gtsleeper]

TFI can cause all kinds of havoc. But I am curious, do you have any gauges in the car measuring air/fuel, vacuum, or fuel pressure? If so, that will likely tell the story.

 

[2011rustang5o]

Tomorrow I'm gonna search for a pressure gauge for fuel but I haven't hooked up a vac gauge yet. Idles great now though. No a/f gauge.


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[Moosee1955]

Tfi' can have an intermittent problem, but usually go out completely. I had a mechanic at my shop years back, that playing around trying to bring up dtc codes without a scanner, using the jumper method, blew out the tfi module. Ending up towing my mustang 23 miles, because the bone head said I had a blown timing chain. This was 20 plus years back, and I trusted him. Should have punched him. After 6 plus hours of replacement found out he blew my ign module. That would of taken 25 minutes. If in doubt replace coil, put on a Ford high performance one if you can. Again least problems. Keep us posted what you find, it will help other readers. If you want to see if your pick up coil is good, theirs plenty of tests online. Moose!


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[2011rustang5o]

Yea il post my findings for sure. Iv read too many dead end threads on this issue. And too many stupid ass replies too. "Got gas in the tank?" Kinda crap.


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[2011rustang5o]

This damn thing won't start with a factory replacement coil. Weak.


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[mikestang63]

how's the battery. what;s the voltage at the battery and the + coil. A weak battery or bad cable can cause cranking problems.

 

[2011rustang5o]

Swapped back to the MSD and it fired right up lol. Probably plug gap or possibly a bad replacement coil. I'm actually starting to think it's MAF related. It has a filter on the MAF but today I'm swapping to a thru the fender CAI. I'd like to put a air straitener in too but I don't have one laying around.


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[jrichker]

From the Surging Idle Checklist.

MAF meter on CAI system that needs clocking or protection from engine compartment air turbulence. A cone type filter located inside the engine compartment is almost sure to have surge problems due to the hot, turbulent airflow around it.

Don't do this: it is a big NO NO.

[

Try cleaning the MAF element & then "clock" the MAF by rotating the entire MAF housing to see if changing its position helps any.

What codes did you get when you dumped them? No diagnostic work and you are just throwing money, sweat and time at a dartboard in vain hope of finding and fixing the problem. Please list both the engine off and engine running numeric codes

 

[2011rustang5o]

It's not a idle surge issue.


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[Moosee1955]

I agree with richter, you need to run codes, and get a fuel pressure reading, or your just chasing your tail! Sounds stupid but when you installed new coil, did you get positive/ negative right. Easy to mess up when frustrated. And Tess tfi module and pickup coil can cause your problem. Best if you get new ones from Ford dealer, even if you have to order. Oreillys I believe can test your old tfi!


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