Kendall

I recently overhauled my 89. I bought it with a spun bearing so I have no idea how it ran originally. I put the the 383 stroker kit in it. I also installed the most radical cam that Crane makes for stock computer controlled EFI systems (big mistake but different issue). I had to replace the injectors so I installed Ford 24# units. My issue is starting. It starts reliably but you have to crank it a couple of seconds, both hot and cold. I'm hopeing to keep tweaking until when starting, like my 87, the first piston up will fire and purr. Is that an unreasonable expectation with this engine? To get that will I perhaps have to burn a new computer chip? I also have a question about the IAC unit on the throttle body. Is it simply a stepper motor that runs operates a threaded rod that has the plunger on the end which seats to control idle air? This next weekend I think I will take my throttle body off and clean it up by glass beading it. I'm hopeing that will help. Any other ideas or responses would be appreciated.

Thanks
Kendall Herrick

Nathan Plemons

What if you turn the key on for a second or two before you actually crank it. I know mine will crank for about a second before it starts if I just hop in and turn it over. If I turn the key on for 1-2 seconds before I actually try to start it that allows the fuel system to pressurize and it'll fire in half a revolution.

It's not real bad on mine because it holds it's fuel pressure well. You might put a gauge on it and see how long your car holds it's pressure after you turn it off. It should hold for hours.

ZylaRace

The IAC is just a stepper motor.
The 89 does not have a cold start injector. The reg injectors take over this job. Don't use the 87 programming for the 89, or alter the cold start settings in the 87 to compensate for the extra fuel needed.

Kendall

I typically wait until I hear the fule pump stop before I crank it. I forgot to mention I raised my pressure to 50#. That may change because I'm still in the "tune up stage" with this rebuilt motor. It holds pretty well. Even overnight it will still be sitting about 30 or so.

Kendall

Thanks. Thats what I thought. Mine has a little bit of white rust on the shaft. I was considering just getting a new one to be sure things were optimal. That was one reason I thought I might take the TB off glass bead it--to make sure the seat on the IAC was nice and clean. I presume that a new one "retimes" itself once you install it?

Nathan Plemons

Yes, the new IAC will come with instructions but there isn't really an adjustment. You just have to make sure that the needle isn't too far extended to begin with.

Kendall

Another issue which might be related is: Where should I set my initial timing? Right now its at what the compartment label says: (6 BTC I believe). I heard people recommend 4 degrees advance over factory specs which would be 10 BTC with a race cam.

Nathan Plemons

Can't help you there, the LT1 has no timing adjustment. Try to talk to Scorp508, he's good with that motor.

bill mcdonald

My 90 when stock, started on first hit of the key as well.

I built my motor up including a cam and now it takes a few seconds to start.
I did the key trick and waited for the fuel pump to shut down, it makes no difference here.

I also run my timing at 8-10-12 degrees (I play with it a lot). with this cam it likes timming on my combo. I also have an MSD knock sensor monitor, so far so good.

Kendall

I suspect a little of it is the computers inability to cope with the cam. Allot of experimentation burning new chips might fix it. I'm a little disappointed in my cam. It was advertized to have torque/power from 2000-5500. My goal wasn't to go over 5500. I really wanted the step down that was advertized to be strongest from 1500-5000. Crane claimed that the extra cubes would tend to bring the 2000 figure down. Well it didn't, if you put you foot in it at 1500, about the time you get to 2000 it feels like someone turned on a set of thrusters. Sure works good from there on. My problem is that the car has a ZF6 and since the motor is mush under 2000 I can't legally drive it down the hiway in high gear without killing it. Also part of the reason for the stroker crank is low end torque. I'm missing out on 500 rpm of that. If someone disagrees with my logic feel free to do so. I'm open to opinion on this.

PeteL

Here is a good step by step on adjusting the tps and minumum air setting on your car. I would add that disconnecting the timing connector helps. Don't know how lumpy your cam is, but you may have to settle for 500 or so rpm, 450 is the correct adjustment.

[edit to add link]
https://www.corvetteforum.com/techti...D=55&TopicID=2

Think your fuel pressure is way high with those FMS injectors, they really act more like 26 to 28#ers. Might try using a scanner and turning pressure down until the BL gets around 128 in most cells.


[Modified by PeteL, 5:02 PM 9/11/2002]

Kendall

Tnx for the response. You hit on something that has me puzzled. My old injectors were shot so due to recommendations of others I purchased the Fords. The rationale was that Ford are far more sensitive to fuel pressure vs fuel delivery which makes them a little more versitle (sp). My question is since the computer is watching the gases in the exhaust wouldn't it sense the extra fuel and simply cut back on the pulse time. At this point in time wouldn't you be back to the same fuel delivery you would have with a smaller injector. I realize that with the larger capacity injector you can get more fuel to the motor if called for but won't the computer simply adjust for injector size? What am I missing?

I do intend to get all the equipment and start tweaking and burninig new chips but my work tends to be seasonal so I'll save that for next winter. I also need to do allot of reading so I can have a clue what I'm doing when I get there.

Nathan Plemons

The ford injectors aren't really more sensitive, they are just rated at a lower fuel pressure, so when you run them at GM pressure they act like a larger injector.

Yes, you are correct, when the computer is in closed loop it can narrow the pulse width, up to a point. However when you first start it up the computer is in open loop mode and it runs off of some set values, which may now be way too rich. Also at WOT you are in open loop, reading off of different set values.

The computer is really pretty good at compensating for small changes when in closed loop, that's why you don't see a lot of programming for part throttle operations. Everything you see done simply uses the base maps for starup and WOT adjustments.

Kendall

Tnx for the details. You pretty much said what I assumed from reading. I've not gotten to really play with the car that much. I bought it with a bad bearing so didn't get to do diagnostics b4 I tore it down. I don't have a history on it except I bought it as a flood car so I got it cheap. As a twist of luck, I think the insurance co. got scammed. I can't find evidence it has ever been in water. It's fully loaded-- a nice car! Of course it will always have a bad Carfax.

PeteL

I would back off fuel pressure to 40 (vacuum applied) or 48 (vacuum removed and plugged). Do the throttle body cleaning. I would not bead blast, I use TB cleaner and it cleans up nicely. I would get a new GM IAC from Jeff Koop along with a full TB gasket set and screw set. Soak the small screws for the covers for at least a night before removal, they tend to strip on the coolant side.

Before you knock yourself out cleaning the TB, make sure there is no lateral movement in the TB butterfly shaft, as it wears and gets sloppy causing bad idle. There is NO lateral movement in a new TB. It's a little hard to check as the spring holds pressure on the shaft, however with it removed and in your hands you can work it and feel the sloppy shaft.

You really need a scanner to set that fuel pressure.

Pete

Kendall

Tnx for the info. Sounds like need a new TB I have plenty of lateral movement. If new ones have none I'm sunk.

bill mcdonald

I have the FMS injectors too.

I have an in car fuel pressure gauge, I keep mine at 42 at idle with vacuum on. I started out with it at 37, it ran fine like this as well, I fattened it up when I installed the headers. You might want to shoot for this range as well.