I have a 1984 crossfire that the engine surges when not under powr usually
in 14-1900 rpm range. The surge is audible but seldom feelable, the tack
does not indicate the surge, I her it or sometimes feel it. This surge was
there prior to installing a new cam, solids and lifters and rebuildng the
rear (thinking too much play). I am at my wit's end, any suggestions woudl
be greatly appreciated.
The '84 Crossfire is computer controlled much as the rest of the L98s.
A scan tool will read out sensor values.
Biggest difference: this is a Manifold Pressure measuring (MAP) system
rather than a Mass Flow measuring (MAF) system. Once the system is in
closed loop there's not much difference and most of the diagnostic codes
are the same. (Note: Later on Chevy returned to MAP.)
IMO, Eugene is correct that vacuum leaks are more critical in the '84
and this is a good place to start. Haynes has a good procedure for
setting up idle without a scan tool (does involve a balance manometer
Hi PJ I have e 2 84's w/CF (stripping and repaining one and other is
front w/slight frame damage...trying to decide if I should part that one
break up a vette ).... and would like to learn as much as I can about them...
explain what "closed look" means as simply as possible. I have a 92 also...but
driving the 84's more. Great throttle responce and its hard to believe they
rated at 205 hp....thanks apperciate all the help I can get.
I think early C4s don't get as much respect in the press as they produce
off the line. Remember that these cars make max rated torque @ just over
3000 rpm and max horsepower at 4 grand. Above 4K they fade fast. 1/8th
mile times are pretty good, even today. L98's with auto are said, by
some, to be faster than the 6-speed. Not really so--many guys with a 6
speed shift late, thinking that being near red line is the way to win.
Being first in line at a signaled freeway on-ramp is always unbridled
Actually it's "closed loop." Once the coolant temp rises, the ECM
starts adjusting mixture based on what the oxygen sensor is seeing. The
control loop is then: Oxygen Sensor sees more or less oxygen in the
exhaust stream, tells the ECM -- in turn the ECM alters the injector
pulse length which, in turn changes the exhaust content seen by the
OxySenor. All of this gets some anticipation by signals from the
throttle position sensor and (for the Crossfire) the MAP sensor. On
the TPI cars there was no MAP and a 'hot wire' sensor in the intake
provides a signal to calculate mass airflow (MAF). MAP systems cost
less in production and some argue that it works better at altitude than
does MAF and Chevy returned to MAP with the LT-1.
Until the coolant gets warm, there's no feedback from the exhaust
content -- it's an 'open loop' system and the ECM is using constants in
the ECM (Prom) with MAP, air temp and throttle position to compute the
There are far better and more complete descriptions of this in the
Emission Controls section of the shop manual.
I still recall my first '84 ride. One of my engineers got his the first
week. We checked out an accelerometer from the lab, then took it out in
the company parking lot on a Sunday afternoon and produced very close to
that 1.0g of lateral acceleration that made the car famous. Avoided
lube starvation -- as far as we could tell.
good luck with your 84's.
I personally didn't like the cross-fire problems and done
away with it.
put an intake and edelbrock carb in its place.
bored it out 30 over with flat-top pistons and free flow
hooker headers, high output coil and custom made 8-mm wires.
not exactly street legal but now has 375 hp...
Yea, its a lucky thing for now.
but as we both know,
all good things come to an end sooner or later.
When it does, I know what I am going to have to do.
I will probably either do it or sell the car at that point.
I am going to continue to enjoy living back in the 60's and
for now :-)
Key, what was involved with removing the TBI and putting on the carb other
than the obvious removing the physical unit and bolting another? I've
thought about that a couple of times with TBI vehicles because they act like
big two barrels with not enough airflow in the full throttle situations.
(Of course they get better mileage than a 4 bbl carb, bolt a two barrel on
and it will, too.)
But I have never found out what happens when the connections to them are
disconnected. Do you have to jump any or just leave them off or what?
Actually my mechanic done the work.
He just left the unused wiring unplugged,wrapped and tucked
out of the way.
(Incase another owner wanted to restore it back / I kept all
Naturally this caused to computer to throw up many codes, so
we could have removed the warning light but
I just covered it with black tape to hide it. Now have to
pay attention to the guages like we used to do.
He could have plugged up the now unused portions of the
exaust manifold but I desided to just put headers
and keep the old manifold.
We tried to use the old coil and distributor but he was
having problems so I desided to replace the coil with a high
output coil and 8-mm wires and also replace the distributor.
We added an adjustable fuel pressure stablizing unit to keep
the desired fuel pressure.
We tried two different intake manifolds. the first was too
tall and the carb breather had problems clearing the hood so
we had to put a shorter one. We also had a problem locating
a breather system that would clear the hood. Ended up
modifing an eldlebrock breather to allow enough clearance.
Do realize that the car is no longer street legal but I will
enjoy the car and deal with that when the time comes or sell
As far as the milage now, I am getting about 18 mph mixed
city and hwy. Haven't taken any road trips yet.
Still breaking in engine.
The first time I mentioned this on this group, I was given
Can't remember the exact advice but it was something to do
with modifing and upgrading like newer models?
Was also told by a GM mechanis that he could have blocked
off something and used the same carbs.
I really didn't understand what he was telling me because I
wasn't really listening,
Had already went the other way.
Well thats about the best I can dicribe the change.
I am not a mechanic, just a retired locksmith :-)
Thanks to everyone for your responses, I will try to check for vacuum leaks
as that may be the problem, since this problem began I have installed a
Lunati cam, solids, roller rockers, Mallaroy 40k volt ignition, rebuilt the
rear end, and put headers on, I still have some surging. I tend to think it
has something to do with the oxygen sensor or something similair. I guess
the next step is to eliminate the computer altogether and proceed into the
Key, with the cam, solids, roller rockers, mallaroy ignition (40k volts) and
headers I kinda figure i am close to 300 hp and it runs like a scalded
rabbit. I, unlike most, enjoy the tight ride (ex MG guy here) and think
this '84 vette is a true sports car. If I can't dump the surge then the
he** with it, it still acellerates great and sounds great.
'84 arrest red/red
I kinda like the extra power too !
reminds me of the old muscle cars...
growing up in the muscle care era, my best friends dad owned
a chevelet company.
we got to drive all the chevy muscle cars and the others
from the used car lot.
g'day to ya
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