88IROC_CVTFAN

Guys:

I just finished installing a ZZ4 with TPI in my 88IROCZ. The car originally had the TPI 305 and I've moved the gear over to the ZZ4 with the following changes,

TPIS Big Mouth, Adj. regulator, Level 6 PROM
Random Tech Cat and 3" catback system
24#/hr injectors from fuel injection specialties (stock were 18#) These injectors came in GM boxes so I'm assuming they are rochester.

My fuel pressure was set at idle (600 - 650RPM)at 47 psi. I set the timing at 6BTDC.

The engine bogs at low end but shows real potential if you get to mid-range. I'm new at this, having fun, and would like some advice on where to go from here. I will add that I have a bad exhaust leak (I'm getting it fixed today) and was wondering if this could cause part of my problem. The engine now has 70 miles on it.

Thanks

airdeano

whats the inital timing set at? 8-10* is a good
start. tps voltage should be .5v-7v at idle.
the manifold is moving more air than the stock
unit. a scanner will tell you if you are bogging
because of too much fuel or too much air.
fuel pressure is? 42-45# is a good starting
place.
airdeano

JETHROIROC

If 47psi is your fuel pressure with the vacuum line connected at idle, then your pressure is too high. Try 42-45 as airdeano said without the vacuum line connected (engine shut off). Hope this helps.

------------------
1990 IROC 350
Mods: Too busy trying to make it run right to mod it.
Airfoil, Dynomax cat-back, MSD coil, 180 t-stat, Bald Eagle tires,
Hypertech fan switch, Accel 23# injectors, Holley module, ported plenum,
Ported Daytona Yellow stock base, Moroso valve covers, other stuff,
Streetdampr, Ruger P95DC, hot wife, new oil filter, !cats, !TBC, !AIR.
18.0 @ 85MPH since I'm one big-a$$ MF
"It's better to have and not need than to need and not have."

88IROC_CVTFAN

Thanks,

What you both say makes a lot of sense. When I first fired the engine I timed it by ear to where it seemed to respond well. Then I read the manual, placed the jumper to take the computer out of the timing picture and set it at 6BTDC. Before I set it I looked at where I had guessed and it was at 12*BTDC.

I'll reset the fuel pressure with the vacuum hose disconnected. When I set it everything was connected and the engine was idling.

I've got a scanner that is presently set at the VIN engine code "F", ie, the 305. Should I change this to "8" for the 350, does it make any difference?

While I've got your attention, is it advisable down the road to get the larger runners and throttle body? Should I get a 58mm or 52mm? Who makes the best runners?

Thanks again.

JETHROIROC

Yes, change your scanner parameters. Also, some aftermarket runners could help your TPIS base breathe better, and port the plenum thoroughly while you have it off. I'd say the Arizona Speed and Marine or TPIS runners are the best, but if you're on a budget get the SLP's as they go on sale sometimes. I don't think the throttle body is that much of a restriction right now.

Mark_ZZ3

Set your scanner for what ever config your PROM was designed for ... IE 1988 350.

To set your fuel pressure, I look at the BLM. Try to adjust the pressure (with vac link disconnected) where the BLM is as close to 128 as possible. You may have to adjust the pressure, drive around for a bit, check the reading, etc.

You might want to check that you have a 350 knock sensor, and not the 305 one. I know GM has different part numbers for them. I assume they are tuned differently for each engine.

If your engine is "new" you might want to give it a few mile to break in. I would guess you will have to be "tweaking" things for a while until everything gets in it's place.

It is common on stock throttle bodies with many miles, for the shaft to wobble and cause a vacum leak. While it does not cause too much trouble, it still is an unknown. So there is one reason to consider an upgrade for your TB. 52MM would probably be all you need. I have read road tests where a larger TB actually slowed the car down. Look at GM's ramjet 502 ... it has a 48mm TB. Go figure that one.

Mark.

88IROC_CVTFAN

Thanks Mark:

Setting my scan code to the original engine code worked well (the 305 code "F") Setting it to a code for a 350 "8" didn't. My BLM is at 129 so it's pretty close but I need to scan at different speeds.

Setting the intial timing (jumper in place) at 10BTDC and setting the idle to 800 really helped things but one problem remains. At lower RPM the engine sounds like it's missing on one cylinder. I don't know if it's fuel or ignition. I won't get to work on the car till Thursday because I have to travel this week. Any suggestions for troubleshooting this would be greatly appreciated. The car seems to run pretty strong except for this "stumble".

Mark_ZZ3

Funny, thing, mine sounds like it is missing on one cylinder at idle too. I have checked and checked, but not sure.

I was going to blame one of my injectors for being dirty. It seems like the only logical choice. I did have them cleaned a while back, but who knows what kind of crude has made it's way through. Perhaps they are just getting weak.

It would be really nice if there was a second O2 sensor on the passenger side. At least you would have a better idea if something was out of wack.

Drive your car around for a while (a few miles/days/etc.). Then check your plugs and see if there is any cylinder different from the others. That might point out a bad injector, wire, vac leak, etc.

I have noticed that the outside temp and humidity effect things. I like in the north, so it is getting cooler now. I recall I put on brand new MSD super duper wires and the car idled worse ... well of course it was cold that weak. The next week warmed up and it ran great ... mileage was up, 1/4 time was up. I should have bought a loto ticket too.

Keep me in the loop as to your progress. I would be very interested in hearing about your engine.

Mark.

GTA91

iTrader: (1)

Yeah, keep us posted. I'm building a L98/ZZ4 motor right now and would like to know some tricks of the trade for it. How does it idle? Pretty lopey???? Later!

------------------
'91 GTA:
www.fbody.com/members/91WS6GTA

88IROC_CVTFAN

The ZZ4 lopes real nice. If you combine it with the Edelbrock headers and Random Technology 3" cat and catback it sounds great.

I gave my brother a short ride last night, you should have seen his eyes when I fired it and let it idle - he drives a Volvo. In short it's a real muscle sound.

I just need to get the rest of the bugs out.
Talk to you guys in a few days after I troubleshoot the injection and ignition.

Later