Dream Bikes

A friend of mine has just bought a 82' Crossfire.
The car looks good and has only 17.000 miles.

He's scared about fuel consumption (9 miles per gallon)...that's seems very strange.

What could be?

PhyscoVette

Sounds like its way out of tune. My 82 with with a few mods still gets 18 in town and almost 30 on the highway. I would start with a full tuneup and check the timing. then I would check the fuel system for leaks.

fadingrockstar

I agree with PhysoVette, my 82 does about the same as his.

Shark Racer

Man, now I want an 82 Corvette!

The best I've gotten in my 78, with the previous setup (mostly like an L-48) and a 700R4/3.55 was 19mpg.

PuddleJumper

yah id tell your friend its running way rich. a tune is needed and i might check the pistons,head, and plugs for excessive soot build up. the lab car in our high school shop gose though 2 sets of HOT plugs ever 9 months being it idols ie runs a tad rich all the time.

shark racer the 3.55 rear end is killing the mpg a little. if you put one of those injection carbs on your vette i bet it might get better mpg. but 19 MPG with a V8 is not bad for a 1978 considering what a lot of cars from the 70s get.

82crossfirevette

Same here.

Give us an update on your progress.

Bill Curlee

Ahhha,,the SEASEFIRE ENGINE! Now your talking something I can help you out with. First things first:

Read your engine Diagnostic Trouble Codes and see if there are any being displayed. Its been a while since Ive played with OBD1 stuff (heavly into the C5 OBDII stuff) but its like riding a bike!

Basicly you need to short pins A & B in the ALDL and watch the check engine light. The first code will be a 12 and it will flash the check engine light in a 12 code three times in a row. If there are any DTC set, they will be displayed next. After all the DTCs are displayed, it will flash flash a 12 DTC three times .

Heres a GM OBD1 code reading overview:

Re: obdI code reading


it should flash each code 3 times 12 12 12 then it will flash the codes stored 3 times each then it will flash 12 12 12

GM common codes for OBD1 (for vehicles made before 1995)
12 System normal
13 oxygen sensor circuit open
14 coolant sensor high resistance or shorted
15 coolant sensor circuit low or open
16 direct ignition system (DIS) fault in circuit
17 cam position sensor fault
18 crank or cam sensor error
19 crank sensor circuit fault
21 tps sensor out of range
22 tps sensor signal voltage low
23 intake air temp sensor out of range, low
24 vehicle speed (vss) sensor circuit fault
25 air temp sensor sensor out of range, high
26 quad-driver module (computer) circuit #1 fault
27 quad-driver module (computer) 2nd gear circuit
28 quad-driver module (computer) circuit #2 fault
29 quad driver module (computer) 4th gear circuit
31 cam position sensor fault
32 egr circuit fault
33 map sensor signal out of range, high
34 map sensor signal out of range, low
35 idle air control sensor circuit fault
36 ignition system circuit error
38 brake input circuit fault
39 clutch input circuit fault
41 cam sensor circuit fault, igntion control circuit fault
42 electronic spark timing (EST) circuit grounded
43 knock sensor
or electronic spark control circuit fault
44 oxygen sensor lean exhaust
45 oxygen sensor rich exhaust
46 pass-key II circuit or ps.pressure switch circuit fault
47 pcm-bcm data circuit
48 misfire diagnosis
51 calibration error, mem-cal, ecm or eeprom failure
52 engine oil temperature circuit, low temperature indicated
53 battery voltage error or egr or pass-key II circuit
54 egr system failure or fuel pump circuit low voltage
55 a/d converter error or pcm not grounded or lean fuel or frounded reference voltage
56 quad-driver module #2 circuit
57 boost control problem
58 vehicle anti-theft system fuel enable circuit
61 a/c system performance or degraded oxygen sensor signal
62 engine oil temperature high temperature indicated
63 oxygen sensor right side circuit open or map sensor out of range
64 oxygen sensor right side lean exhaust indicated
65 oxygen sensor right side rich exhaust indicated
66 a/c pressure sensor circuit low pressure
67 a/c pressure sensor circuit or a/c clutch circuit failure
68 a/c compressor relay circuit failure
69 a/c clutch circuit head pressure high
70 a/c refrigerant pressure circuit high
71 a/c evaporator temperature sensor circuit low
72 gear selector switch circuit
73 a/c evaporator temperature circuit high
75 digital egr #1 solenoid error
76 digital egr #2 solenoid error
77 digital egr #3 solenoid error
79 vehicle speed sensor (vss) circuit signal high
80 vehicle speed sensor (vss) circuit signal low
81 brake input circuit fault
82 ignition control (IC) 3X signal error
85 prom error
86 analog/digital ecm error
87 eeprom error
99 power management


If you can read and post the displayed DTC, I can help you resolve this issue.

You most likely have a sensor that provides the ECU information that isnt providing the correct info.

Could be as simple as a bad connection or a bad sensor. Read and post the codes and lets resolve your issue!

Bill Curlee

gerry72

It could be how your friend is driving the car, it could be his math in calculating the fuel economy. In those cases, there could be nothing wrong.

Outside of driveability issues, and you didn't mention any, OBDI systems are sophisticated enough that you can read the datastream to look for clues of something not right even though the car seems to otherwise behave normally. Your first step in diagnostics is to first determine the status of all available sensors. One thing that won't show up on a scanner is a clogged converter. But, again, you'd have some driveability issues.

7T1vette

Tell him to run a 'mileage test' by filling up just before going on some highway trip, then fill up again immediately after returning. If his highway mileage isn't around 20 mpg or better, there is some problem with the sensors/control system. Check codes as shown above (if there are any). Often, there are no codes for such situations; but some sensor is 'on the edge' of failure so no code is thrown...but performance may be degraded. MAF sensor and oxygen sensors are likely culprits in such cases.

Sean82

The 02 sensor will fail rich so that you do not run the engine lean.
- the o2 sensor should be changed regularly as it wears out

The coolant temp sensor tell the car when it is warm enouph to not need the extra choke fuel.
- the coolant sensor may have failed cause the computer to never seeing the car as warm and not needing the extra fuel.

7T1vette

Run the "highway mileage" test. It will tell you whether there is some funtional problem with the fuel control system or not. Don't fix what "ain't broke".