This client's story starts with another addition to their Z32 addiction. The vehicle didn't come with any proof or paperwork to suggest the timing-belt was done recently or ever from any previous ownership, so the client did the responsible thing and had a mechanics shop install a new VG30 grenade pin... aka the timing-belt.
Post belt replacement the motor ran well enough but seemed to "slow down" with more throttle input until a high RPM level was achieved. The client was refused any sort of follow-up inspection from the mechanics maintaining they had done everything correctly and it was a "300ZX" thing. This client, having owned several Z32s in their life begun some self diagnosis...swapped ecus, AFM, 02 sensors and even sprung for a new genuine idle system setup from the States and still behaving like an "Un-FairladyZ"
With as super light throttle was possible, the car drove into #ConeptAutoInd for a thorough inspection & a few side-quest issues - now poor idling/running & not so speed sensitive power steering
Having been personally told by the previous mechanic who's "been in the industry for 'X' years and couldn't get a timing belt service wrong an on old POS like this ra ra ra...", we started with the usual suspects - resetting all the base mechanicals, the CAS timing, TPS & Idle control, smoke test & we managed to clean up majority if the rough idle issues.
Cylinder Compression test just incase = wasn't particularly low but was even to 2-3PSI, nothing really stood out with a Leakdown test, the motor ran too well to have piston kissed valves & didn't make bad noises all the way to redline.
Now we don't like playing the "blame the last guy" game when customers come to us from other shops, but now the recent timing work was the last item left on the board of possibilities. Pulled the pass side timing cover off (easy side) & peeled the drivers side case off the backing plates slightly & cam marks appeared to line up with a Zeroed harmonic balancer so everything seemed legit.
At this point I didn't want to start major teardown until i was absolutely sure it wasn't something either external or electrical. Made a booking with tuners to run it up on the dyno and get some eyeballs on the live data of what's going on. In the weeks waiting for the dyno run, we rechecked all investigations to make sure i hadn't missed anything, after all everyone makes mistakes that's how some of us choose to learn things.
Fast forward & we are now watching the details on the dyno live, watching this engine make MORE vacuum with throttle, we worked down the facepalm list to arrive at possibilities like valve float, major internal issue or something amiss with timing.
This is when I suggested that the Cust engage previous company to double check their timing - If they have any respect for the services they charge their Cust's for, they should at least have the honor & decency to check/inspect their work...apparently not & how dare the Cust have the audacity to question their monkeys on tools!
Now disheartened by the previous workshops response & attitude, the client gave me the go ahead to start digging and thus began the descent into the VG30DE abyss. Intake hoses off, radiator drained & out, water outlets of the motor, drivers & lower timing cases completely off and bingo!
The VG30 timing case marks aren't exactly 100% spot on but it did appear that the Drivers Head Cam-set was out by more than the usual "halfish" tooth to the Pass side. Counted the belt teeth and confirmed the drivers side cam set were indeed a tooth out. Because timing-case marks can lie, we reset the timing belt using the marks provided on the belt (work smarter not harder!) and resealed water outlets. Added the radiator, coolant and intake hoses and a quick test drive and the thrusting torque you would expect from an VG30DE with no apparent engine management issues was found!
Since we had now inherited the mechanical responsibility for this chassis & for absolute confidence in our skills & performance, we inspected every other aspect of the the previous shop's service. We came to the conclusion that the front crank seal could not have been replaced in this "major" timing service because the crank sprocket had not been removed.
We Re-Performed our complete "Major Timing Belt Service" in full with all new componentry to maintain control & insure this VG30DE future is as safe as it can be.
This is why a Specialist Technician who is fluent in these particular Chassis, Genre & Age of Technology Vehicles with extensive experience in these critical tasks should be engaged. #ConceptAutoInd prides itself on transparency with its works for our clients and it is upsetting that this instance cost the clients several times over to resolve.