Author Topic: 87 Runs like a dog. (Read 20341 times)

Vettech · « **on:** February 11, 2014, 12:14:06 PM »

Have 87 - was running OK - now has a rolling miss, when pushed it farts and back fires - If didn't know better I'd say the "Timing' was out - disc the timing plug, T'Light on #1 and it shows ~6degs. This is about correct. But when the plug is disc - idle drops (but tacho says ~600rpm) and it runs even worserrrrr. Put on new leads, only codes I have are variable 33, 34 & 36 - ie air too low, too high and MAF burn off issue - these reset OK. I have little hair left but am at the hair pulling stage - I can't stand issues I can't diagnose from the books and symptoms
If this was an older style motor/ignition set up, I might say it was the vacumm advance but !?!?.
May have to change my handle. Any ideas greatly appreciated. Vettech.

69VETTE · « **Reply #1 on:** February 11, 2014, 12:38:24 PM »

Hello Vettech,

I know if you haven't driven the car for a very long time, the analog computer,may if the battery hasnt been on a trickle charger go wonky, well not run spot on. .so when you start it up its all over the place and idling up an down and give you the symptoms you have described.

I had the same issues with mine when I purchased my car cause she hasn't been driven for over 7 months even with a trickle charger.

At the moment she's running beta but still occasionally runs odd. . only constant driving has sorted this out.

Hopefully some other C4 owners can shed more light in this matter.

Vettech · « **Reply #2 on:** February 11, 2014, 01:27:35 PM »

Thanks 69er - The car was idle for many years - but was rego-ed again in Dec '12 and has been on many club runs etc - and has been going very well. EXCEPT for the heating issue which I have not mentioned - maybe now will be a good time. Cold the car started and ran well, run for 30mins ++ and stop and try to restart within say 15mins and it sounded like either a flat battery or it was in the process of ceasing - but the actual water / oil temps were OK. Having said that it would always start after the second or third full rotation, BUT sometimes it would give a VERY LOUD "ping" so loud it really sounded like it had hit a valve - but once running it ran well no noises or issues - power to burn. I think I will remove the Starter motor and either rebuild or replace with a reduction drive style. Also renew the main cables, lugs etc and fit a thin light weight S'Steel heat shield.
Regards. Vettech any thoughts are very much appreciated.

Vettech · « **Reply #3 on:** February 11, 2014, 01:35:02 PM »

OH! - something else on what you said - in a 87 and maybe all C4's the computer has what is called a "Block Learn" section in the memory - so if you wanted to go dragging - drive to the raceway disc the battery for 10-15mins - reconnect and then race it up and down the carpark or road as if dragging (6~8 times) this then tells the processor that you want that style of driving - and changes the Shift Hysteresis of the Box, the timing etc the result should be better times etc.
Sorry I digress.
Regards. Vettech.

69VETTE · « **Reply #4 on:** February 11, 2014, 01:37:33 PM »

Your welcome. I was told by the previous owner that whilst the analog computers have there good points, they also a somewhat primitive. It sounds like your on the right track.

If you still have problems, contact Steve Rosenfeld at Rockdale as he is very knowledgeable on these units.

69VETTE · « **Reply #5 on:** February 11, 2014, 01:39:04 PM »

Sounds awesome, and yes they do have a memory ... I was told that too, mines a 1990 Vette.

MY081 · « **Reply #6 on:** February 11, 2014, 04:15:16 PM »

Amate of mine who doesnt use the forum just rang and said he had that very same prob . He says its the mas air flow senser he said if you like you can ring him on 0409724442 to talk to him his name is Greg .

Jethro · « **Reply #7 on:** February 11, 2014, 06:02:16 PM »

Hmmm, I think I have a New Adjustable MAF Sensor laying somewhere I bought for my 1988 C4 but never used..... P.M me know if your interested ?

Jethro

Vettech · « **Reply #8 on:** February 12, 2014, 10:26:04 AM »

Thanks everyone - Whilst trying to sleep I had an appithany (where's the spell checker) last night and thought it may also be the ESC - Electronic Spark Control unit, but this would normally set a Code 43 - So before any more I'm off to work to download all codes - if no 43 then I will ring Greg.

More than likely your Greg is on the money since Codes 33, 34 and 36 are all MAF related issues. I've checked the associated relays and their contactor resistances and they check OK. But my gut still tells me that detonation, back fires etc upon acceleration are a function of timing, vac advance etc. So I will pack up and off to Minto to see what codes I now have - I'll try and refrain from taking the 1 gallon can of petrol with me.
Regards,
Vettech.

77CVT · « **Reply #9 on:** February 12, 2014, 12:18:32 PM »

If you can find someone with an 87 you could swap MAF to confirm? Apparently 85-87 are different MAF's but I have swapped (briefly) with no issues.

Here is a rare example of something that can happen (to me) with similar symptoms - my earth cable was moving an intermittently touching the exhaust. Probably not your issue but worth checking.

Disconnect your battery for 5 mins and take it for a run. If you only have the MAF related codes see if you can swap it with a working one.

I cannot see the point of a learning mode. All that data is hard programmed into the chip. It will only change if you buy the software and flash a new one.

oh, and check the knock sensor wire on the rhs of the block. Sometimes mine comes loose and cause issues.

Good luck.

Vettech · « **Reply #10 on:** February 12, 2014, 04:01:52 PM »

Ok - thanks 77CVT for your reply.
I'm at work and set up to read the codes and got 33, 34, 36 aaand a 42222 what the - I expect a 43 not a 42, 43 is the EST - ie the module in the Dissy that changes the Pick Up (points) signal to drive the Primary Coil winding of the EHT Coil. Reading Manual. Ah haaa! the last time I did the Timing Light I disc the bypass or "Set Timing Connector", I must have left it open cct. No it was OK, but still had the codes - penny drops - disc battery - reconnect start codes again and sure enough all codes now reset. Start car - you can still here it running like a dog. Drive up street and give it some boot - still no codes but it is still missing and occasional backfire.
Now - 77CVT - thank you I have checked those items - the book also says check them as they are the most likely to cause issues. On ECM - yes it has a whole lot of stuff "HARD' programmed into it and you can change the chip to give other specs. But the ECM is only a Computer and can only give "X" if inputs "A ~ Y" have certain values. So a section of the memory is called "Block Learn" and as I said it sees what you are doing and sets the parameters for max power or efficiency or what ever you require - ie Dragging. BUT - this is volatile memory and if battery is disconnected the memory is wiped.

Jethro · « **Reply #11 on:** February 12, 2014, 04:05:43 PM »

Don't shoot me for asking

However Fuel is o.k ?

Vettech · « **Reply #12 on:** February 12, 2014, 04:18:55 PM »

Ummmm! - Fuel - well there is only a range of 41Kms - so it is nearly out - this has been running like this for some time - and I'm sure it was filled at Blackheath on the return from some Bathurst Pub run, El President I think also filled up - Caltex. It drove home fine and back to the warehouse OK - and a few short runs into CBTN, then started playing up.
ONE Thing I have not done is remove the PLUGS. I replaced all leads. Took out #8, was OK - like brand new. But it was a PITA getting back in - I had the horrible feeling I was cross threading it ERRR. So I have not removed any of the others.

The fact it has still ample power and backfires when pushed could indicate one or two not firing and when the fuel gets into the exhaust it ignites - backfires.

Vettech · « **Reply #13 on:** February 12, 2014, 04:23:19 PM »

NO NO - I'm talking rubbish - it was refilled for the Dam Xmas run - where !?!?. But ran OK - was only back in the w'house going for a short run or a test that it started this problem prior to Xmas.

But it could be fuel - I might shout it a new fuel filter.

Jethro · « **Reply #14 on:** February 12, 2014, 04:31:51 PM »

Quote from: Vettech on February 12, 2014, 04:23:19 PM

NO NO - I'm talking rubbish - it was refilled for the Dam Xmas run - where !?!?. But ran OK - was only back in the w'house going for a short run or a test that it started this problem prior to Xmas.

But it could be fuel - I might shout it a new fuel filter.

And a new tank of fuel

VETTENUT · « **Reply #15 on:** February 12, 2014, 07:22:57 PM »

And a bottle of Techron Concentrate fuel system cleaner from your local Caltex.

Jethro · « **Reply #16 on:** February 12, 2014, 08:11:42 PM »

Quote from: VETTENUT on February 12, 2014, 07:22:57 PM

And a bottle of Techron Concentrate fuel system cleaner from your local Caltex.

A Gazza Retired but still a Caltex boy through and Through

Vettech · « **Reply #17 on:** February 12, 2014, 09:15:48 PM »

Caltex rubbish - poo.

77CVT · « **Reply #18 on:** February 13, 2014, 08:56:24 AM »

I had a dizzy module cr#p out on me half way through running in a cam! Ran like a dog - lucky I had a spare. I don't recall if it threw a code out or not.

I'm guessing it's something electrical/electronic. Pity you'r not near me or you could swap all my parts to find the problem.

Scott · « **Reply #19 on:** February 14, 2014, 08:59:05 AM »

After disconnecting the battery, rather than waiting 10 minutes generally you can just press the brake pedal for a few seconds. The brake lights will drain the remaining charge from the ECU (and the radio) and erase any saved settings.