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Hesitation In Throttle Response

I love my Chevy Chevette!
Posts: 7
Joined: 02/13
Posted: 07/19/13 05:56 PM

I am the owner of a 1987 Corvette that I am at once in love with and hate. My wife found the Corvette at a Used Car lot back in January of 2006. Knowing that I had owned a 1970 LT1 Corvette as well as a 1973 with the RPO LT82 (250hp) engine. My wife thought it was high time I had another Corvette; after all it had been some 32 years since my last Vette. We bought this one without doing any “comparison” shopping of what else may be out there since this one seemed to be in near show room condition and drove that way with no visible signs of being involved in any accidents.

We both fell in love with the Corvette and enjoyed driving it immensely. About a month into ownership is when the “hate” seed planted itself. That’s when, on my way to work driving down the Freeway, the right banks head gasket blew it’s top. No big deal I thought as it did have 123,000 miles on the odometer. I firmly believe that this Vette was, and with me, is a daily driver. Hey, give me a break; it’s my only car. My wife has 2 vehicles while I have this one in my name. With head gasket replaced we jump ahead to November of 2011 and a cracked block (between pistons 6 & 8) necessitating in a new engine block. I found another Corvette guy who happened to be “an engine builder” and had a freshly built 350 intended for his sons Camaro. This was complete with a high-rise manifold and a Holley 750 cfm carb on it as it was intended for a 70’s model Camaro. Being I had the L98 in the Corvette, the intake was replaced with my TPS system. Leaving the rest of the motor as it was built. With a Comp Cam, non-computer controlled of course since this was for a 70’s Camaro build, Flat Top Racing Pistons (10:5.1 compression), along with everything new from the oil pan on up to the Holley. My L98 heads went to the machine shop for proper machining and cleaning while being updated to accommodate 1.6 Stainless Roller Rocker’s, all new valves, guides etc. I’ve changed the thermostat to a 160-degree and ECM programmed for such. All told, it ran like a bat out of hell. I was in love again, an engine that carried me past the factory rating of 245 hp to what is believed to be reaching skywards of 350 to 400 hp potential.

Here’s where my latest “hate” comes in, and with only just over 3800 miles on this new engine. Let me add here that the ’87 Vette is with the 700R4 automatic. I also have short tube headers with a single Cat & a pair of Summit Racing- racing muffler’s at the back. The Fuel Injector’s are newer Bosch III 22 lbs set at 43.5 (adjustable) Fuel Pressure on the regulator. (I haven’t replaced the diaphragm in the regulator yet as it did not need to 3000 miles ago, perhaps now needing?). The timing is set at 6 Degrees BTD with the idle in gear at 650-700 rpm’s. The TPS is set at .56 mv as required by the ECM programmer with code 89 delete (cold start) & the cold start injector disconnected. I live in San Francisco so no need for this. Everything is new including all sensors, wiring, and vacuum lines. Let me simplify things here, everything is new. The runner’s & Plenum have been machined and honed. A set of SLP runner’s & Plenum are at the machine shop now getting machined up for installation along with the Throttle Body to match for 52mm.

Before I install the SLP’s I need to find out why this thing, it seems at a certain rpm range, hesitates, burps, whatever when driving and especially when sitting at a light idling. When the light turns green, I go for a ways then the hesitation when speed is picked up & shifts into the higher gear. This has gone on for a couple of weeks now. I have checked & replaced any vacuum lines showing a need to do so including the one at the left rear wheel area (fuel return vacuum line). Found my #2 Accel plug wire nearest the header had burnt thru so replaced all 8 wires along with the Cap & Rotor. I have done everything that I can think of. My mechanic friend suggested I check the EGR Control Valve Relay Solenoid, which I not only checked but replaced as well. I am thinking that I may need to replace the EGR Valve Temperature Indicator Switch yet again. But I am not getting a code 32 as it would if a bad switch. The only code I am getting is a “normal” code reading. By the way, the injectors pulse just fine if that is a thought.

With what all I have done so far I have all but eliminated the hesitation except for short burps of it if I sit at idle in traffic too long. It also has caused on 2 occasions now shown blue smoke coming from the tail pipes. This greatly concerns me. What with new O2 sensor and knock sensor etc it mostly runs great, except this short hesitation problem. I did find that the oxygen sensor had been bent slightly while the exhaust was being worked on & installed so I carefully straightened it. It was only slightly bent and not enough to be damaged from a visual stand point.

I am at a loss here and really could use some help. Either I get this thing right or I s-can this Corvette and get what I want in a C5 Corvette or go back to a pre-1974 Corvette. Being old school I have never been fond of computer’s in cars or a variation thereof. I have grown to appreciate what potential there is in these newer LS engines and the whole computer thing but afraid I am more preferential to the basic carbureted engine, even a Fuelie, minus the ECM et al. Whatever help or suggestions you may have I would be greatly appreciative.

I wrote this lengthy detailed explanation this morning and on my way to work it not only hesitated it started to run like on 7 cylinder's by time I got to work, freeway driving. This is where my thought on the EGR Temp Sensor Switch comes in as it had happened to me once before. Managed to clear it up on my way home from work and it ran like on 8 cylinder's again but a bit rough and only a slight hesitation this time. I have considered checking again the pulse on the injector's along with the connector's/wires as well as the Fuel Filter, Charcoal Cannistor and the Cannister Purge Valve, just in case. When I got home this evening I plugged in my Actron Code Scanner into the Diagnostic Connection and sure as hell the engine ran "Perfectly Flawlessly" until I shut off the motor & started it again without the Actron connected. This lead me to believe it was the EGR Temp Sensor Switch so... Just what is going on with this thing?

Never Mind!!! I just found the problem and once again it is the damn EGR Temp Sensor Switch. I have found that at some point in the past day or two the wire somehow got twisted and just came off in my hand. Have ordered a new one so now I wait for it to be shipped & delivered. Word of caution for my fellow C4 owners, and the Camaro/Firebird owner's out there who have the L98 motor installed, with this Cross Over Tube from the right manifold/header to the intake manifold. They may without warning go bad or the wire "burns" (remember~ it gets extremely HOT here) as mine appeared to do in the past day or 2 as I've said & loses connection and/or breaks free completely. Major internal damage may be done if not checked regularly.  
Gregorio Lonewolf

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I mow my lawn and find Chevys
Posts: 2337
Joined: 03/10
Posted: 07/20/13 05:42 AM

glad to hear you got it figured out.    those motors are sensative to any emmisions equipment failures.  

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I mow my lawn and find Chevys
Posts: 1994
Joined: 10/09
Posted: 07/20/13 06:29 AM

Glad to hear you've found what ails your ride. I know it can be a major buzz-kill when it's not performing to its potential.  
68scott385 68scott385 68scott385

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Big Block power for the win
Posts: 868
Joined: 12/11
Posted: 03/06/14 09:31 AM

I know this is Way Old,  but put A 190 Degree T-Stat Back in, the Computer thinks it's still Kold.  

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