Hi Guys,

Just got an 87 IROC-Z last weekend, and she's getting about 8mpg right now. Stinks like unburnt fuel at all throttle positions, and is burning a bit of oil. The last owner told me it'd probably need the stem seals doing to cure the oil leak, but my main priority at the moment is trying to get her back to a stock fuel tune.

I don't know a great deal about the history of the engine, but do know that several years ago heavy duty gears and a shift kit were installed on the trans, so it's plausible that the block has been messed about with and isn't standard. It does have log manifolds still and a single pipe back to the rear silencer, so my guess is it's probably unlikely that much was done to the engine though.
The engine has had the A.I.R disconnected and bypassed, and a check engine light popped up on my way home from buying the car, but that hasn't come back since...

From searching the forums I believe I need to check:

1. Injector resistance is 12 ohm
2. Timing is 6* BTDC
3. Base idle - she's idling around 1100rpm currently and settles to about 900-1000 when warm.
4. Temperature sensor resistance?
5. MAF relays & MAF
6. Fuel pressure
7. Vacuum leaks

Is there any else I've missed, and is the order right?

Thanks!

 

Idk about the order, but checking the O2 sensors wouldn't be a bad idea either while you're at it.

 

I shall add that to the list. Is it as simple as what's stated here: https://www.thirdgen.org/o2tuning, just without the goal of adjusting the fuel metering to change the reading?

 

I honestly don't know, I'm not running a computer/o2 sensors/emissions. Reading through it the process sounds plausible.

 

Right, so, looks like it's at the very least an injector issue.

Left bank is 11, 17, 5, 17
Right bank is 17, 17 5, 17

That'd be over fuelling and under fuelling, right, which would explain why she's running like a dog at the moment? Where's the best place to get injectors, given that I need to get them shipped to the uk?

Also adjusted the iac, she starts hunting around 550rpm and dies at 500, so the base idle is set to about 575 until I can sort the fuelling problem. Tweaked the tps as that was out by 100mv as well, and the improvement in throttle response had me leaving my yard sideways >_>

 

Southbay fuel injectors would be the best bang for the buck as far as injectors.
You will have to contact them though to see if they will ship to the UK.

 

Zane, thanks for the recommendation. Yes, we ship world wide!

 

Awesome, I shall give you guys a call to see what I need then!

 

Thanks to Frank @ SouthBay's great advice, 8 x 22lb injectors and a gasket set shall soon be winging their way to me!

 

Got my new injectors from southbay to here in the UK too mate, top notch service My Trans Am was running terrible when i first got it, the main cause of which was indeed the o2 sensor so if yours looks manky as hell then id probably swap that out too while your under the bonnet doing the injectors

Scott

 

It's still on the todo list at the moment thanks to my shop being full of other cars that need fixing before I can get mine in the air to look at it. Didn't fancy trying to get up and under all the EGR crap to get a reading off it or pull it to look!

What tires are you running on your Trans-Am and how do they hook off the line? Considering importing a set of something from the US thanks to how crap the selection here is.

 

Went with the 19's as we discussed. Went out today. Also refunded the over payment on the shipping. Sorry about that. Keep us posted

 

Ive just got regular tyres on mine as i dont really thrash it around, I do spin the wheels a fair bit and it gets sideways when i want it too which is good enough for me

That was with my 305 TPI so im eager to see what its like after i finish dropping the 350 in

 

the idle sounds a little high.

what I would do if I were you is just do a tune-up or at least inspect all of the typical tune-up items (distributor cap/rotor, plugs, wires, filters [fuel, air]. in the process of all that, I would check the out the MAF relays & MAF meter for sure. timing, fuel pressure, vacuum, also can all be checked in the course of a tune up.

 

That's what I thought too!

I have a tonne of parts winging their way to me, and in the meantime I've been tackling the stuff that's pretty universal, including systemic vacuum issues. Think I'm going to have to replace every single hose in the bay as all of the tiny plastic pipes are so brittle that if you even look at them, they snap. I did discover one running across the firewall off the T below the wiper motor, which just ends abruptly near the a/c tank and wasn't connected to anything. I've temporarily plugged that until I can figure out where the hell it's supposed to go (the doors on my HVAC work, but I can't test out whether the heat does too until my heater core turns up).

Also have a Fuel Pressure Gauge to plumb in, and I've been tagging various vacuum hoses with my vacuum gauge to see whether they're losing vacuum anywhere. Fuel pump side is running just under 0.8 bar but the rest of the system is about 0.7 so there's some loss along the lines that I need to fix.

The previous owner gave me all of his spares, which included new leads that need crimping, oil and various other bits, so that's on the todo list as well.

I ordered a rev limiter on Friday, which hopefully will turn up Monday, as she spins the rear wheels constantly, and the techo immediately heads into the danger zone, which scares the **** out of me. Once the limiter's on and set to something conservative like 4800rpm, I'll feel much better about not melting pistons or floating my entire valve train into destruction. I'm hoping the couple of times I've crossed the 5500 threshhold were down to having an inaccurate tacho rather than it actually having gone there.

She's tappety too, so I need to pull the heads and renew the stem seals (loads of oil getting burnt). In all, car is in physically great condition, but the engine really isn't at the moment. The more I look at it all, the more I think it's most likely not just one thing causing the rich condition and crappy idle.

I've got a friend forward shipping me a couple of ACDelco o2 and temperature sensors as I didn't really care to pay $40 in shipping on $35 of parts, so those should turn up week after next along with the injectors, and I'll be in a position to tear everything off the car and start replacing things. There's a coolant leak somewhere as well that I've yet to identify - nothing's pooling under the car, and nothing looks wet, but the coolant level is slowly going down. Hopefully it isn't the head gasket on its way out, though I haven't found any signs of that in the oil.

While I was looking over the vacuum hoses, the carbon canister found itself suddenly sat on the floor looking glum (don't ever leave me alone near your car with tools if it has a carbon canister fitted, unless you want it torn out that is). Should save a couple of lbs on useless weight!

And she went through her test today with only two advisories about the headlights being totally useless, she failed hard on emissions last week, so it's nice to see that the few bits i've been able to do have made a bit of a difference. Not gonna be happy until she's purring and ready for silly cams and other fun stuff though.

 

Cool man, sounds like it will all come together soon the way your going ! the carbon canister has been missing on mine since i got the car and whoever took it off just capped off the pipe that runs from the back of the car to the engine bay and it seems to have been fine

 

Fingers crossed! She's got a tap I need to figure out as well; hoping it's top end, but I've got a stethoscope coming so I can go over it. Funnily we've never needed one in the shop until now as we mostly do 4 bangers.

I did basically the same thing with the vent pipe, milled a slot into the end of some threaded rod, and wound it in then put the hose clamp back on. Looks pretty decent IMO.

 

Keep your old injectors. They might be just fine.

 

This might help eventually:




You post is not entirely clear. Fuel pressure should be over 2.5 BAR. If the gauge indication is correct, there is a significant problem.

If you were referring to the vacuum reading, at idle the reading should be closer to 0.45-0.55 BAR (absolute). A slight difference at the FPR port is expected since the vacuum source is port adjacent to the throttle plates. If the throttle body is not clean and not adjusted properly for minimum air position, the difference can be greater. Both of those things will ultimately have to be re-checked once it is running more normally, but it wouldn't hurt to verify those items now since they can contribute to poor idle. Setting the TPS voltage might also be helpful.




If the engine is running THAT rich, there is a good chance the oil is contaminated with fuel, causing a substantial loss in viscosity and lubricity. If that's the case, it would be good to drain/replace the oil NOW, before and serious damage occurs.

 

Hmmm... So going off that diagram, if the doors are operating, then everything else should be as it's just a single feed to the whole control system?

Where would he disconnected vacuum hose that was headed across the firewall connect then?

Yeah, those were the vac readings. It may be that the gauge is off (it is cheap Chinese crap). I tweaked the IAC to as low as it would go before idling and set the tps right at .540, she ran a little better after that - certainly more responsively. I'll add cleaning the throttle body to my list of things to do during my evenings this week!

She's locked up in the garage for the week now, but I'll do an oil flush next weekend with semi-synthetic that we keep in bulk. I'm planning on pulling the valve covers and checking for rocker play as well.

May ask a friend who owns a test centre on the same lot as my workshop to do a hydrocarbon test on her and see exactly what's coming out the tailpipes too.

 

Woo, good news at last. Rev limiter arrived today, and I just got done fitting it a few minutes ago. Tested it out set at 2500rpm, and according to the tachometer she started bouncing off the limiter at 3500. So it looks like it might be out by a fair bit, but at the very least, it means I wasn't actually hitting 6k rpm while spinning the tires! Time to go look at aftermarket tachometers I guess.

 

There is a member that refurbishes/sells factory tachs if you want to keep things stock. I don't recall his user name, but some forum searching should find him for you.

 

Thanks dude, found his post, shall have to add it to the never ending list.

Parts turned up today from rockauto, sadly they were badly packed so 3/4 headlights were destroyed on their way over. They're shipping me new ones. I did get my new heater core fitted though, in the middle of a hailstorm! Uncanny timing really.

I also decided to make an aldl cable, and after a few issues and bits of cloudy information, I got winaldl talking to the car. Apparently the ecu thinks she's idling at 1200, but I'm not sure how much of that is due to needing ports a and b bridged with a 10k relay to get comms functioning.
It also told me that I've got ses code 33 and 36 active, so I'm having a friend grab me a couple of relays while he's on holiday in NYC. Probably going to end up having to change the MAF as well, but I figure I'd try the easy thing first.

I need to do more testing, but according to winaldl, the car ain't entering closed loop after startup and stays in a rich cycle; it also thinks the coolant temp is 145F after being sat for 4 hours in freezing temperatures. I don't think so Tim. I'll check again tomorrow after she's been sat for 24hours and see what it thinks then but I've a coolant sensor on the way anyway.
I think I need to get tuner rt working next so i can see what's going on in the tables and find out what other shenanigans are taking place.

Advice appreciated as always

 

Hokay... winaldl data log done on an average drive with a couple of bits of acceleration; couldn't get tunerpro rt working in any way that gave me the data I wanted, sadly. I've dumped the log into google docs and started to put together a couple of charts, but tbh I'm more used to looking at tables that tell me where in a map the car is and metrics that tell me what it's doing rather than raw data. Can anyone lend a hand decoding what it's saying?

The spreadsheet is here, and is editable: https://docs.google.com/spreadsheets...AI4clJPzBZN88/

 

Okay. Time for an update to this as it's been over a month and I'm starting to make progress. It turns out that basically every sensor on the car was ruined in some way or other, including the MAF sensor (which had been replaced shortly before I bought the car). I looked at the prices of a replacement, laughed a lot, and then ordered a megasquirt. I decided to go with the TPI adapter board and built it up inside a TBI ecm case, so it looks completely factory to the untrained eye, and means I haven't butchered my loom. This is good, because the entire last week has been trying to get it to start and run properly and switching between ECUs to be able to move the car.
Last night, I nailed that, got the timing set properly, then dialed in the VE table to get the idle smooth (it also turns out that I have a sticking throttle body, which explains the high idle issues I was getting, and the increased difficulty under light braking).

Here's a screenshot of the current idle on the car, in comparison to the 900-1100 rpm idle I'd get before. Still need to tune the rest of the VE table to get it in a driveable state, but so far so good, and not much rich misfiring or eye-burning exhaust.

The other benefit I've seen so far, is the off-idle response is ridiculous. It snarls when given a light tap of the throttle instead of taking its time. I think this was easily the best $600 I've spent on her so far, and one of the more interesting electronics projects I've worked on.