Vn 5L Miss under load (pretty long read)

[moodybluebobParticipant View build HERE Member since: March 4, 2015 Posts: 44]

Hey guys, recently completed my engine swap from a V6 to my worked V8. Ill give a rundown of events leading up to the problem.

– Completed conversion, drove fantastic, didnt miss a beat. Tuned by ACE performance.
– Upgraded exhaust system (Hurricane Headers, twin 2.5″ 100 cell cats, merges into a single 3 with one muffler, then merges to twin 3 after the diff.)
– Drove for a while good, then started to miss a touch under load. Just a little, figured it was the intake choking at high rpm.
– Continued to drive it about once a week, problem started to get worse. Would take off and it would shut down and almost stall, letting your foot off the accelerator slowly and ittd fire back up to life.
– Had an instance where it happened, pulled over, and when i’d touch the throttle ittd cough and splutter. idles perfectly fine though.
– changed 02 sensor. also tried different ignition module and coil. Problem still there.
– Found leads were melting a little around the connectors, replaced leads and installed aftermarket heat shields. Still the same problem.
– Did my torque power manifold change. All new sensors on the manifold. new manifold gaskets etc. drive for about 30 minutes like a bat out of hell, thought awesome its fixed! Gave it a run in second gear, it about 4000-4500 RPM and it started to miss, like on limiter almost. put it into 3rd and accelerated as normal, dropped back to second and the same problem high in up the revs.
– Got to a set of lights, gave it a boot in first, and it lost all power and almost stalled, rolled off the throttle easy and it kicked back to life. Drove it home just cruising all fine. idles fine.

– Popped the bonnet and found my belt has flipped itself somehow. Could this have caused the miss? Would a slipping alternator belt cause such a problem?

Here’s where im thinking of going to next.

– New belt of course
– Change the plugs (what plugs do people recommend?)
– Look into fuel system (has a new walbro upgraded intank pump and LS1 injectors.)
– New dizzy

I’ve checked fault codes, none found before manifold swap, after the swap, Code 12 flashes 3 times & 22 shows up after. (TPS signal low voltage). I’m assuming this is being caused by my proflow throttle body. Still idles and drives fine until the miss occurs, and since it was doing it before the change, i dont think that’s the problem.

anyone ever experienced anything like this? any help would be greatly appreciated.

[ACE PERFORMANCE TUNINGParticipant PENRITHL98 VX SS ON NITROUS AND VS 304 View build HERE Member since: March 14, 2015 Posts: 48]

Tps will cause issues like you have described id get a new one.

New alt belt wont hurt either.

[vnssnvParticipant victoriaWhite, red and grey vn ss View build HERE Member since: March 2, 2015 Posts: 26]

The wiring loom to the sensors gets very brittle after 20 odd years of getting hot and cold.

If you have replaced the tps. Id check the wiring for broken wires.

Very common for the cts wiring to break also.

[VS 5.0Participant Perth WAVE SSV Z Series M6 View build HERE Member since: March 31, 2015 Posts: 118]

I recently had a similar problem with accelerating from standstill where it would miss and almost stall unless I rolled of it. I was also experiencing a miss with moderate acceleration from cruising at around 1600 – 1800 rpm.

Turned out the dizzy cap was arcing out on the rotor button which was blackened. Changed those two and all is good.

[ACE PERFORMANCE TUNINGParticipant PENRITHL98 VX SS ON NITROUS AND VS 304 View build HERE Member since: March 14, 2015 Posts: 48]

It logged a code so its basically telling you what the problem is.

I agree about the wiring ive seen plenty of bad wiring,broken plugs etc

due to the age of these cars.

A lot of the time people go replacing parts and its actually a wiring issue.

Seems some of these aftermarket tps switches are bad quality too

I swear by eldebrock and fast they are good quality products.

Holley are good too.

 

[moodybluebobParticipant View build HERE Member since: March 4, 2015 Posts: 44]

cheers for the reply guys.

I’ve just stumbled upon something. A standard throttle body opens the throttle clockwise relative to the TPS. On my  proflow tb, it open it counter clockwise. Could this potentially be my problem? and what would be the way to go to fix this?

[ACE PERFORMANCE TUNINGParticipant PENRITHL98 VX SS ON NITROUS AND VS 304 View build HERE Member since: March 14, 2015 Posts: 48]

Wouldn’t think so unless you used a standard tps.

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