My 89 was just (7-22-11) tuned and dynoed. She passed with flying colors -Max RWHP=469.65, Max TQ= 451.17 This on a 107 degree and 13% humidity day.

Drove her home, 40 mil. drive, and put her in the garage. Two days ago a took her for a ride and after driving for about 30 min. I was making about 80 mph and the tach was on 2, then the tach started to jump. It went from 0 to 5 in a rapid movement back and forth. The speed whent from 80 to 49 mph in the high way without warning. Needles to say the car was shacking all over. I was shifting up and down trying something to see what could work but nothing work. I pulled over and had her towed home.

I called the people that did the tune up and they are suggesting that I change the computer. Right now I have the Accel DFI VII with upgraded CALMAP and wideband kit. They are suggesting the FAST.

The question for you ladies and gents is, Do you think this problem is computer related? If no, Do you have any ideas on what to look at? and if it is, how is that?

The guys at the Dyno shop are telling me that the Accel sys. is unpredictable and problematic to tune. . . They say that they were hopping that their tune was going to hold for a while but it seems that it did not. Any thoughts?

Thank you for your help

Luis

 

Go find another tuner. The ecm has nothing to do with the speedo or tach or the other gauges except the mpg readout. Your problem is obviously electrical. Check the battery, terminals, alternator and grounds.

 

. . . battery is brand new (a week old), grounds are new (they went over them during the tune up), that would leave the alternator to be checked. Excuse my ignorance, but, how do you check your alternator? what I would be looking at to determined if it is working correctly or not?

Thanks

Luis

 

Your problem will be difficult to diagnose because it is intermittant. I would recheck all the grounds; battery to chassis, block and bellhousing. There are also 3 ground wires that attach to the middle bellhousing bolt on the left side. I know my dash goes goofy if one of these are left off. It's possible a bad ignition key circuit may be creating a problem. As far as the alternator, it might be shooting ducks, but you can try a replacement to rule it out. It really sounds like your tuner wants you to pay extra bucks for a new engine management system so you can pay them more buck to install and tune the thing when your solution lies elsewhere. Good luck. Willie

 

That was my first impression about my tuner, he wants "mo money". I have been thinking about the intermittant part of my problem trying to find a pattern and it seems that every time I rev the car beyond 2500 or 3000 rpms is when the problem starts. I have not have time to check the alternator yet but I am doing it as soon as I can. The other thing is that it was not doing that before the tuning and they change the belt because they said that the old belt was too long, do you think this has any connection with the problem in some werld way?

Thanks again

Luis

 

I'm a little confused, did your speedo also erratically fluctuate like your tach did? If it did then I agree with the posts concerning your grounds etc. If not then it usually points to an ignition problem, such as a distributor, control box (such as the MSD) or its associated wiring. A tach is a great ignition diagnostic tool. I would not totally rule out the Gen VII but if it is, just replace it, your great tune will load in and go, why re-invent the wheel?

Concerning the Accel Gen 7, before I retired and as a former Accel EMIC (certified and trained Accel Engine Management Installation Center) I have installed and set up approx 80 of them for many different applications. Unlike the previous Gen 6s, I have never had any problems with a Gen 7, always considered it one of the best systems available. Usually it was the first thing the customer questioned if they had a problem but it always turned out to be something else. However this has been just one man's experience and things may have changed by now, they never stay the same.

 

When you say the tach was on 2, you mean 2,000 rpms?

When you say the speed went from 80 to 49mph, did the guage fluctuate while the car's speed remained unchanged? Or, did you actually get a sudden decrease in speed?

"Needles to say the car was shacking all over". Are you saying the car shook during decel? Did the shaking continue below 49mph?

With the engine running 2k at 80MPH, does that mean you have a ZF6? If so, did the shaking continue after you disengaged the clutch and/or thru it out of gear?

 

The '93 I bought in February had the same problems -tach fluctuating wildly, engine miss, then dying. I did all the opti, coil and ICM related diagnostics for DTC 36 and didn't find anything out of spec. I checked all of the electrical connectors and spark plug wires and they looked good.

After I had cleaned off the grunge around the coil I noticed the coolant hose on the passenger side of the throttle body was leaking underneath . The ground for the tach filter under the hose was really dirty so I disasembled it, cleaned and put it back together. The car hasn't faltered again.

I'm going to replace the coil and ICM if only because the PO replaced the opti a year ago and those other parts are original.

Doe anyone know if the coil windings are supposed to wobble on the 'frame'?

This video explains the optispark with some troubleshooting included. http://www.youtube.com/watch%3Fv%3Dl...BCygYYwZ8N-D0w It's from GM.

I'm not saying this will fix your car but it worked for mine. Hopefully you have a manual and follow it when trouble shooting. Othewise you're you're just "you-know-whating" in the wind. I've seen a lot of people simply spend money and change parts without understanding what's wrong first in my very short C4 ownership experience.

 

Yes I mean 2000 rpm. The speed did not fluctuate, it decreased gradually as the car failed tu respond to the gas pedal. The tack was all over the place regardless what I did. I tryied changing gears (I have a zf6) but every time I released the clutch after shifting the tack will go up and down erratically and the car will chake. It actually went to 0 rpms a couple a times and the car stalled at 30 mph. When the car was in neutral the tack did not shake but that's when it went to 0 rpms.

 

In that case, I gotta agree.....OPTI.

 

Any chance it is the slave? I just saying, the OP had problems with the slave cilinder in the past.

 

Wow, that motor is consistant in its output! That definitely sounds like like the MSD box. I got that box used so its time may be up. You can try removing it or rewire to circumvent. that would rule it in or out. I doubt its the Accel system unless something worked loose. Keep an eye on the alt as it is (was) an NAPA pos. It seemed every time I had it on the dyno and we spun it close to 7K, the plastic vanes would disintegrate. I had lifetime free replacment so I would just stick a new one in. Take a flashlight and look in to the case and you will be able to tell if its in one piece. Lastly, look at the coil, I seem to recall that when I had that dual snyc opti distributor installed with the separate coil, the coil was interfering with the dist signal. Maybe something got bumped. Just some thoughts

 

Sure sounds like an Opti failure. I'll bet the rotor let loose. Also make sure to check all the connections associated with the ACCEL Gen 7. Its very important to solder and shrink wrap all these connection.

 

89 was not OptiSpark...its GM HEI.

This is more of a MAF or MAF relay problem from what the op is trying to describe. Bucking, rpm drop/jump when at cruise speed, not wanting to take throttle...

Ck the wires to the dist & module inside. Check the MAF plug and its relay. The problem is a simple sensor issue.

When the op says "tune"......what does that mean? spark plugs and wires? or did they take the existing prom and reprogram it?

 

new valve cover gaskets
new racing plugs
new wires
new dual sync dist. w/ bronze gears and moroso shims
new battery
new ground straps
new rack and pinion
new rear wheel bearing
new rear brakes
new serpentine belt
new outer tie rod end
new temp sensor
new u-joint straps & bolts
new half shalf U-joint
new axle stubs
all electrical wire solded were needed
all electrical wire thermo shield wraped
new 16lb radiator cap
oil change. . .
Dynoed and tuned

 

I plead insanity. Between the "shacking" comment in the OP and Mr. Thomas posting about the OPTI, I got lost/confused. This thread has taken several days for replies, probably because of the confusing OP.

Neither dynocar nor myself could determine if the car actually bucked/shook or if the dash display just went crazy. And, the car lost power and slowed to a stop. lumij3 said "the speed of the car did not fluctuate, it decreased gradually".

This implies a flat-out loss of power/signal. While I've had my MAF fail on me, it did not cause the tach to jump wildly. Hard to think that's the problem. It seems more likely this is a distributor or electonic timing issue. (That's why I was so easily thrown to the OPTI comment".

If there's an MSD box on this car, that's one place to start. Lots of MSD complaints/failures over the years. If the reference and/or tach wire gets connected to the MSD box, there's your reason for the possessed tach reading at failure. You could also consider distributor wire (after ruling out the MSD). ECM (and/or it's plug/wires would also fall into the group of suspects. If non-OEM software/computer was used for tuning, add that too.

 

The op has an Accel Gen 7 engine management system. No proms needed, just a laptop.

 

[QUOTE=GREGGPENN;1578590079] This thread has taken several days for replies, probably because of the confusing OP."

We lost power for a period of time due to a tropical storm that hit the north east, this is the reason why this trhead has taken several days for replies.

"Neither dynocar nor myself could determine if the car actually bucked/shook or if the dash display just went crazy. And, the car lost power and slowed to a stop. lumij3 said "the speed of the car did not fluctuate, it decreased gradually"."

The car loses "speed" gradually at the same time that I am attemting to do something about the tack going crazy up and down. The car is not responding to any gear shifting up or down. the only difference with the tack is every time the clutch is pressed the needle goes to 0 rpms and a couple of times the engine goes off as the car keeps rolling down the road by the momentum carried from the initial aceleration. In other words: the car is going at 80 mph, out of the blue the tack starts going from 2,000rpms to 5,000 rpms to 3000 rpms to 0rpms to 5000 rpms to 3000 rpms to . . . you get the point. As the tack does that the car responds to that movement of the needle by going from 2 to 5 to 3 to 0 to 5 to 4,000 rpm so the car "shakes" or runs in bursts of power instead of keeping one smooth movement foward. As long as the clutch is depressed the runs smooth but there is no power going to the tires, the car is just rolling by momentum, just cruising in neutral if you may. As it does this the car loses speed. As long as I keep changing gears and pressing the gas pedal the tack keep doing the same. The car becomes undrivable and it need to be towed. I hope this is a little more clear. I am frustrated with this issue since I have had the car towed home four times and I have not being able to drive it more than a total of 100 miles since I bought it last year.

1989 Convertible 6spd
Engine:
434 ci
Dart "little M" block
Deck Height 8.990
bore 4.160
Eagle Crank (forged)
Eagle forged rods 6"
Diamond forged pistons -13.4 (11.5 comp ratio)
total seal Pmoly rings
Comp Cam small base circle cam 254/260 .672/.661
Crower forced pin oil lifters
Brodix 227 T1M2 heads
Edelbrock E-Victor intake port matched to heads
Accel TB 1300cfm
Comp Cams 1.6 RR
Stud girdles
42lb green top injectors (flow tested)
Custom air intake
Hooker 1.75" super comp headers
Accel dual sync distributor
New oil pump
Much more........
570chp on engine dyno
470 rwhp on chassis dyno
Accel DFI VII with updated CALMAP and Wideband kit

Thank you guys for your responses and keep them coming. I will let you know what works.

 

Ok...
I get the Accel mngt kit.

The thing that I question is the "tuner" statement or claim that they thought this tune would "last"...
a "tune" does not wear out. A "tune" is basically software.
Hardwear will wear out. Hard parts, like Accel parts that were not properly handled or tuning beyond its ability.

If this is part of the tune then its part of the program thats able to be seen on the screen. I'd treat this like any illness and get a 2nd opinion.

I'm not an Accel fan, not at all. Wasted too much money on generic performance stuff that just did'nt improve anything, except accel stock.
A 2nd opinion should tell you if you (or where) you wasted money, on the tuner or the hardware.

I "get" what you;re describing with the tach bouncing around...thats why MAF came to mind...as the engine bogs from a huge misfire it tries to die or not fire as the rpm was going up...if its an auto it lets go of the trans and rpm drops until it fires again....bucks and burps. hard to take throttle. If its a stick the driver will start to clutch it and that allows the rpm to fall instantly, showing a wild drop until the clutch engages again and saves it from a stall and it'll fire again.

You could D/C the maf if it were a GM ECM and force it to run open loop...that tells you lots right there.
but theres the accel eng mngt........

 

Hey guys, this is an 89 with an Accel Gen 7, normally a speed density system meaning that it uses a MAP instead of a MAF sensor and as mentioned previously, no OptiSpark. It sounds like an ignition problem, if OP installed a used MSD, I think he may be finding out why it was for sale. Usually if a tach goes wild, the problem is in the primary side of the ignition system such as distributor, ignition control box or associated wiring. However, in rare occasions I have seen the secondary side of the ignition cause tach fluctuations, such as an intermittant shorted coil.

OP, FWIW, for performance, reliability and parts availability, I used a stock HEI Vette distributor on my C4 that I raced for a few years with a 600+ HP, 13.5:1 compression ratio, small block 427, up to 7500 RPM. This does not require an external box such as MSD. Never had one ignition problem and it was comforting to know that if I ever did, an O'Riellys was usually near by no matter what state I was racing in. Keeping the HEI stock is key to reliability, no aftermarket modules or coils. Accel can supply an adaptor harness for this distributor. It requires a couple of changes in the Gen VII concerning the ignition input and output plus resetting the base ignition timing.