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Car Forum / Chevrolet / Chevrolet Corvette / November 2006'84 engine surging
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. Art '84 crossfire arrest red/red On non computer controlled engines, a lot of time surging was caused by a vacuum leak. Can you put an engine tester on it (obd) and see what it says. Could give you clues. > 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, [quoted text clipped - 8 lines] > '84 crossfire > arrest red/red  SignatureEugene Blanchard http://www.catsasskustoms.com Parts, Performance, Passion News for Motorheads > On non computer controlled engines, a lot of time surging was caused by a > vacuum leak. Can you put an engine tester on it (obd) and see what it says. [quoted text clipped - 12 lines] >> '84 crossfire >> arrest red/red 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 though.) --PJ Checked all of the vacuum, had an intake leak fixed it and stil lhave surge, I am thinking injectors? > > On non computer controlled engines, a lot of time surging was caused by a > > vacuum leak. Can you put an engine tester on it (obd) and see what it says. [quoted text clipped - 27 lines] > > --PJ Not the injectors....replace the egr valve and the egr control .. >> On non computer controlled engines, a lot of time surging was caused by a >> vacuum leak. Can you put an engine tester on it (obd) and see what it says. [quoted text clipped - 27 lines] > >--PJ Hi PJ I have e 2 84's w/CF (stripping and repaining one and other is hit in front w/slight frame damage...trying to decide if I should part that one out....hard to break up a vette ).... and would like to learn as much as I can about them... Please explain what "closed look" means as simply as possible. I have a 92 also...but enjoy driving the 84's more. Great throttle responce and its hard to believe they are only rated at 205 hp....thanks apperciate all the help I can get. Ken >>> On non computer controlled engines, a lot of time surging was caused by a >>> vacuum leak. Can you put an engine tester on it (obd) and see what it says. [quoted text clipped - 35 lines] > > Ken 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 fun--good KITA! 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 mixture. 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. SignaturePJ '89 auto coupe, '02 6-spd coupe >>> On non computer controlled engines, a lot of time >>> surging was caused by a [quoted text clipped - 56 lines] > > Ken 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 exhaust. hooker headers, high output coil and custom made 8-mm wires. not exactly street legal but now has 375 hp... g'day Signature"Key" ===== >>>> On non computer controlled engines, a lot of time >>>> surging was caused by a [quoted text clipped - 66 lines] > > g'day Must be nice to live in a place where the tailpipe cops don't ream you a new one! -- PJ >>>>> On non computer controlled engines, a lot of time >>>>> surging was caused by a [quoted text clipped - 73 lines] > -- > PJ 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. although, I am going to continue to enjoy living back in the 60's and 70's for now :-) g'day "PJ" Signature"Key" ===== 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? > good luck with your 84's. > I personally didn't like the cross-fire problems and done away with it. [quoted text clipped - 4 lines] > > g'day > Key, what was involved with removing the TBI and putting > on the carb other than the obvious removing the physical [quoted text clipped - 9 lines] > 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 the parts) 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 the car. 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 different advice. 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 :-) g'day Signature"Key" ===== >> good luck with your 84's. >> I personally didn't like the cross-fire problems and done [quoted text clipped - 7 lines] >> >> g'day 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 carburation realm. 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. Art '84 arrest red/red > > Key, what was involved with removing the TBI and putting > > on the carb other than the obvious removing the physical [quoted text clipped - 71 lines] > >> "Key" > >> ===== > Key, with the cam, solids, roller rockers, mallaroy > ignition (40k volts) and [quoted text clipped - 8 lines] > Art > '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 -- "Key" |
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