87_gta

Good Day,

Have an odd problem with the IROC.....

Just getting the car ready for summer and getting on odd chugging type thing going on when car is in OD mostly, It will also do it in D but not as easily.
When driving under very light throttle, in OD (mostly) and RPM is 1500 and speed is around 70 km/h. The car starts to chug, If you put it in Park the issue is not there. To me it does not feel like a spark issue but possibly something fuel related? There is fresh fuel in car, it feels like its just not getting enough but only at that RPM, just under 1500 and its fine, just over 1500 and its fine as well.

When driving if I hold 1500 rpm the issue will steadily happen when it starts, kinda gets a bit worse the longer you hold it. When I apply just a bit more gas there is a slight blip in RPM that occurs and after that all is well again.

It literally only happens when the conditions are just right. When you drive it the way a Camaro is supposed to be driven you may never even see the issue happen. I just don't want this to get any worse.

Any thoughts.....?

Cheers,
-87_GTA

87_gta

Just want to add some more info for what I have checked on the car since finding this issue.

- checked idle settings, TPS and IAC. Performed adjustment because TPS needed it. No change.
-reset timing. Few years back I advanced the timing by fair amount after I got the mini ram. I have since but it back to just over factory spec. and yes i did this properly.
-i have pulled a spark plug. their not worn. look normal. slightly white on tip on plug but no much. look normal
-inspected all spark plug wires. all appear ok and none are touching or have ever touched the exhaust.
-pcv valve is not seized or anything

I was thinking to check fuel pressure on a road test and see if there is any oddities while this issue happens. My other thought is maybe something with the trans (hopefully not).

thoughts.......
(attached photo of spark plug for reference)

spark plug photo for reference

MSgt Luttrell

Sounds like the torque converter is trying to stay locked out at too low a vehicle speed. Here's an article about the issue.

https://www.onallcylinders.com/2019/...que-converter/

87_gta

Thanks for the reply,

I have disconnected the tcc at the brake switch. There was a change in the sense that the issue became less pronounced. But it still did it.

Ill check out that link.

Thoughts.....

87_gta

Another thing I just thought of.

My speedo is not correct at the moment. I have 3.70 rear gear and have not yet had the speedo adjusted. Could this affect anything? its off by about 10 KM/H.

MSgt Luttrell

The TCC solenoid could be hanging allowing fluid to lock out the converter when it shouldn't, that said, since the car doesn't die when you come to a stop, it would sound more to me like the solenoid hanging up when it's deenergized. Here's a few things to try..................

https://www.liveabout.com/diagnosing...roblems-262653

MSgt Luttrell

Yes, it could cause you some issues, generally, the TCC will engage at about 50 mph and disengage at about 45 mph. If the speedo is off by a little, it may not be disengaging soon enough, causing the shudder at slow speed you are having..

GeneralDisorder

iTrader: (1)

If this is the 355 with the mini-ram in your sig..... I have to ask.... has it been properly dyno tuned for this combo?

GD

87_gta

Thanks for the info about the tcc. I will read through this.

In terms of the dyno tuning. No I have not done this but I do have the PROM that TPIS suggested. I gave them a full list of mods that were done prior to ordering all the parts for the Mini-Ram. I have had the mini ram on the car for at least 4 years now with no issue with it. Also when got the Mini Ram I had gotten a new AC Delco distributor assembly and installed at the same time.

Not sure whats going on. Car could use some new spark plugs but they are not worn out by no means. Wires all look ok. When I disconnect the TCC at the brake pedal switch the issue becomes much less noticeable. When its connected it goes back to surging/chugging but only at 1500 rpm. As far as I can remember this was not a problem when I parked the car for winter,

Also what would I need to calibrate the speedo?

GeneralDisorder

iTrader: (1)

You need to look at live data and check what the BLM and INT are doing under these cruise conditions where you get this surging. I suspect it could be an O2 or MAF problem.

To calibrate the speedo..... see my post on using the Dakota Digital box. Apparently they have discontinued the SGI-5E but they have a more sophisticated replacement that can do the same thing:

https://www.thirdgen.org/forums/tran...gital-sgi.html

GD

87_gta

I do agree that I need to get my hands on a proper scan tool to see live data while this is happening. Check 02, MAF, TCC operation and such.

Admittedly I do have access to a snap on scan tool just not at the moment and go figure I actually recently acquired a GM TECH2 scanner but it doesn't work with the 87 ECM. Would work with 92 tho

To further your point about the O2 or MAF sensor. For the O2, if it were that. Wouldn't it only be a factor while in closed loop. I went for a test drive today with car not fully at temp (i know without scanner its hard to tell if its open or closed loop) and it did exhibit the symptoms still.

Appreciate the help....keep it coming please.

Vader

I would agree with the above suggestions. The TCC issue was even noted in a GM TSB in late 1986, and the PROM was altered to increase the lockup RPM.

Since you have tried to disable the TCC with no success, it may be time to disable the EGR valve and test it again. That same TSB indicated a change in EGR apply parameters to relieve the chuggle/shudder experienced at part-throttle cruise.

Fast355

iTrader: (2)

I am thinking ignition misfire. Plugs, Wires, Cap & Rotor and possibly ignition coil. I had a TBI doing the same thing at one point. Was 100% ignition.

87_gta

Thanks for the reply,

I have no EGR Valve with the Mini-Ram, I have the TPIS prom that deletes the EGR but the TSB I found #91-149-6E: SERVICE ENGINE SOON LIGHT POSSIBLE FALSE CODE 32 which does talk about TCC operation. Could be something here.

Ignition wise there possibly could be something there. Plugs not worn but well used, Do plan on ordering new ones. Wires are ok Taylor wires blue ones. Coil tho I admit is old. Not sure if/when it would have ever been changed. Distributor is 4yrs.

I will check into any TSB's regarding the issue with the TCC. I have found a bunch so far this one #87-304-7A: POSSIBLE INOP. TORQUE CONV. OR RELATED CONDITION - was related to CTS operation that I found interesting. My cooling (primary) fan always runs with my a/c removed and I know there is that connector next to the coolant pipe pass side. I have not grounded that out. Could that cause an issue? I will say tho, me it really doesn't feel engine related. I am leaning toward a TCC issue or something similarly related but I wont rule out anything until checked.

I will post back.

Thanks for the help, suggestions are appreciated.

GeneralDisorder

iTrader: (1)

Live data is key. It will tell you when it's locking and unlocking and also if there are any misfires, etc. The O2 will go lean on a misfire.

GD

Fast355

iTrader: (2)

Not necessarily...The 02 is only reading one bank on these cars.

87_gta

So small update.

I will be getting my hands on a snap on brick scan tool later this week so hopefully that will shed more light on things.

Also went to a drive in the car today. As usual car feels good overall but I may be leaning more towards an engine issue, once I got the car back in my garage I found that I could feel a possible misfire. When I would adjust the idle slightly from the throttle body directly I could feel the misfire/chug. Mind you it was not nearly as noticeable since there was no load on the engine. I have ordered some new spark plugs. Not sure when Ill get them with this COVID-19 ****. May as well rule this out and their due to be changed anyways.

Ill report back when I get a live data from the scan tool.

87_gta

Decided to pull another spark plug today. Just because. Here is a close up of it.

It's definitely due for replacement.

Thoughts on how it looks.

Plug ground is very white/greyish. Electrode is more greyish in colour . Plug was not wet but appears to have dry soot spot on the base of threads.

Fast355

iTrader: (2)

IMO, if you are not doing the wires, cap and rotor you are probably still going to keep on misfiring. The small cap HEIs are particularly sensitive to cap and rotor quality and condition. I used good wires and a quality cap and rotor. Even then my old G-van used to start missing about every 20-30K miles. Change the cap and rotor and it would stop. Wires with excessive resistance will play a big part in eating the cap and rotor. You could really only ever notice the misfire at low rpm and high engine load...aka cruising in OD. It did not seem to care about what the plugs looked like as long as the gap was not bridged. I actually swapped to a large cap HEI with an external coil to rid myself of this problem.

87_gta

Hello,
So I finally have an update to this.

So far I have gotten a snap on scanner and have driven the car a fair amount with the scanner.

First before I start I have replaced all the spark plugs just to rule them out. I have not gotten the new wires yet.

Live data was definitely helpful here I believe. I was able to verify that the issue does in-fact happen weather the car is in drive or overdrive. Issue happens still at same RPM and the chugging does happen when the car engages the TCC. Car will engage TCC weather in drive or OD.

Another observation I made was the 02 reading (scanner shows 02(mV)). All over the place. when the chugging would happen I would see 02 reading go from 34 all the way to 730 and anywhere in-between. More normal reading that I saw was more between 400 to 700.It was more normal when I brought the rpms higher regardless of drive or OD. Scanner did confirm closed loop operation. I believe the issue was still happening when the car was in open loop. Its cold out here still so I had to let car warm up a bit before driving.

Also some other info/numbers the scan tool gave me are as follows (numbers are car at idle)
INTEGRATR_125
BLOCK LEARN_130
FT CELL _1 (SAW 2 WHILE DRIVING)
02 READY_YES
IAC _75
TPS_.56
02 CROSSCOUNTS _15-17
BASE PW (mS)_1.9
A/F LEARNED _YES
MAT_22 CELSIUS
COOLANT _91 CELSIUS
MAF AND AIRFLOW ARE BOTH 10
MAF (GM/SEC)_10
AIRFLOW_10
LOAD/LV8_50
KNOCK_NO
KNOCK RETARD_ 0
SPARK ADVANCE_16
TCC COMMARD AND 4TH GEAR _P1
OD SWITCH _ON

Anyways that just some of the numbers I got from the scan tool.

thoughts..........

Thank you.

Fast355

iTrader: (2)

Misfiring will show as lean or low 02 sensor voltage output from the oxygen in the unburned intake charge being dumped into the exhaust. The integrator will rise which increases the injector pulsewidth. The richer mixture when it fires will spike the 02 voltage and cause those crazy swings. If cap, rotor and wires do not fix it, try the coil. Torque converter lockup at that RPM is putting alot of load on the engine and therefore more cylinder pressure. Higher cylinder pressure means more voltage required to jump the plug gaps. If the ignition system is not capable of creating the required voltage you will get random misfiring and chugging. What ends up happening is the spark will fire after TDC at random times in some cases as well. I have had a single bad wire arcing out cause a very annoying misfire.

87_gta

Good day,

Spark plug wires will be here tomorrow. I did find that the wires are not gripping the plugs as good as I would like. I have Taylor 8mm wires coming (is what is currently on the car)

Are any of the numbers shown from the scan tool showing red flags? or do the numbers seem normal (give or take)
When I was running the car the scan tool would show lean/rich and cycle constantly between both.

Thoughts?

ASE doc

Toggling O2 voltage is normal closed loop operation. If you graph O2 voltage and INT, you will see the two toggling together. Injector pulse width toggles along with INT. That's how the system works. It is correct that misfire produces lean AFR and low O2 voltage It is also true that the low O2 voltage pushes INT higher, along with injector pulse width. Aside from load related enrichment, this toggling occurs at a pretty high rate of speed and wouldn't be what you are feeling.

Something to keep in mind is that you are running a 355 with a Miniram intake. I assume the engine is modified to make good use of the Miniram's wide flat torque curve and upper rev power. This is not a combination famous for low end torque. You also have the TCC setup to lock in 3rd and 4th gear. There are numerous possible combinations for TCC wiring on the 700R4. Having the TCC lock up at too low vehicle speed, at the lower end of the engine's torque curve is likely to cause the engine to lug and produce the very type of surge you describe. Another possibility is the TCC cycling on and off at that particular engine speed and load. If the factory ECM TCC control is still in place, you should be able to tune the ECM to lock the TCC at a lower MAP value. This will work a little better with your Miniram and will still provide TCC operation during low load cruise conditions, where it's intended to work.

87_gta

Thanks for the reply on the scan data.

As for programming I have a custom PROM that TPIS made for me when I purchased the mini ram. I gave them all the specs for the bottom end of my engine (and trans ie stall and what not) and yes the entire engine was replaced a few years back with a truck block with 4 bolt mains and all new parts. It was a mild build. Wanted a good car for street use. Original block ended up being cracked between the cylinder walls.

Issue only started after getting it out of winter storage. As mentioned I installed the mini ram about 4 years ago.

I did get my spark plug wires in but I was sent the wrong set or a set someone else returned as it was a universal set that already had ends for a non HEI setup crimped on it. .

Ordered a new set and hopefully this does the trick.

I have been using the scan tool a for bit to understand what the car is doing and seeing how the different reading all work in relation to each other. A lot is normal or at least looks right.

One question I find my self wondering is with this misfire/chug, would the knock sensor pick this up? Currently it always reads knock as no and is not retarding the timing. It did read yes at one point after I replaced the spark plugs but only did that briefly.

Thanks for the replys.

ASE doc

The knock sensor will not pick up misfire. It responds to metallic noise, like ping/knock. The knock sensor may pick up knock even before it is audible. You would see this under acceleration, mostly under heavy load. It could be present when the TCC engages under moderate load, before the point where the ECM unlocks the TCC. Look at Knock Retard. it should give a number value. That is degrees of timing being retarded to remove knock. If the ECM is retarding the timing more than few degrees due to knock, it will worsen the lugging issue. Certainly making sure that the engine tune is solid is good move. The symptom really sounds to me like TCC engaging at too low vehicle speed, too high engine load. The Miniram on a 355 with TCC lock up at 70Km/hr sounds like a recipe for lugging. That it just started this year and not sooner is what strikes me as unusual.

With my IROC's 355 with ported large runner TPI, the ZZX cam, and 3.23 rear gears. I find that TCC lockup in 4th gear at less than 60mph feels like too much load on the engine. I don't like to enable the TCC, which I have set up with a switch to prevent lockup, below 2,200rpm. That's with TPI. Granted the big cam does move the torque curve northward so less low end torque, but still more low end than the Miniram. Your higher numerical rear gear is a help for sure, but you still walk a fine line at lower speeds with TCC lock up. I'm swapping in a 9" ford rear with 3.70 gears this summer. Then, i'll be working on completing a custom intake based on the Edelbrock Pro Flow XT. It's a tunnel ram with about 1.5" longer runners than the Miniram. With the ZZX cam it's torque curve on the 355 will be moved northward about 1,000rpm from that of the TPI. I don't expect to be using the TCC below 60mph with this setup. It will be better once we swap to a 400cid in the next few years.

87_gta

Ok so I have an update.

Got the wires installed. No change.

Drove with scan tool some more and found that I was able to get the misfire regardless of TCC on or off.

I am going to pull the cap off the dizzy and check it out. Is there a good way to test an ignition coil?

Cheers,

87_gta

Hello All,

So I do finally have update to this. Been busy with other things lately.

I did install new cap and rotor. The old cap and rotor had wear marks on the tabs. Car runs better than before but the chugging is still happening.

Any other thoughts?

At this point I have done cap, rotor, plugs and wires. Scan tool shows no codes.

Could maybe a fuel filter be the cause of this? I have gone ahead and ordered one but just curious on opinions.

Cheers,

LAFireboyd

iTrader: (3)

How long has it been since you've changed the oil in your 9-bolt? Your sig says it's been rebuilt with 3.70 gears, so it's obviously not original to the car, as it is. Was it installed with the new engine, which I believe you said you've had for about 4 years? And it's run fine during those years, until now, when you just took it out of winter storage? Fresh gear oil with a dose of limited slip additive in your 9-bolt might be in order.

Back in the 90s, my car was behaving similarly. I, too, thought it was engine-related. My Pontiac dealer took it for a drive with me in the passenger seat, and immediately he said the problem was my differential, varnish on the gears. They changed the oil, put in the additive, and everything was perfect again.

87_gta

Hi,

The differential was done mid summer last year. I have a thread on here with pictures of the build and parts used.

Issue only started when car came out of storage.

I have the fuel filter now. Well see what happens after the change.

Cheers,

87_gta

Another update to this.

Swapped fuel filter and decided to double check IAC and TPS and performed adjustment again.(used scan tool to set TPS) Also double checked TV cable as well.

Car is definitely better. I do still feel the issue after this but it is much less noticeable. I do feel (scan tool reading) the TCC when it comes on at the lowest RPM 1400. Car will not chug in the same way but you can feel when that extra load comes on.
One thing I am noticing with the scan tool is the INT and BLM values. I have come to notice the BLM likes to stay higher than the ideal 128. Last road test showed at idle BLM reading of 138 and under light load I have seen it go into the 140's. The INT at idle is saying 128 but does move as well depending on load.

I checked for VAC leaks and I could not find one (at least yet). I do have an AFPR. Perhaps fuel pressure needs to be looked at?

Thoughts,

Update(again):

Checked and adjusted fuel pressure. Set pressure to about 48 PSI with vac line off. PSI will read this with key on or engine running. When Vac line connected pressure at idle is approx 43 PSI. TPIS suggests with the Mini Ram to start at 47 PSI with Vac line off.

On road test with scanner INT and BLM were within what appears to be normal range of 108 to 150. At part throttle cruse with the fuel pressure adjusted I can consistently maintain the ideal 128 now. Mind you it does move from lean to rich or anywhere in between but does not go beyond the normal numbers (numbers based on research I have done. Please correct if I am wrong)

At this point a full tune up (plugs, wires, cap, rotor, fuel filter, air filter, timing, fuel pressure, TPS and IAC adjust and TV cable adjustment) has been done and car is actually running very good.


The issue still only happens when TCC kicks on at the lowest RPM. When this happens I don't see any change that's noteworthy in the scan tool. I do notice the the load numbers on the scan tool go up when the TCC engages but I suspect that must be normal with the increased load at low RPM when TCC is on. At higher RPM's with the TCC on its all good and car is smooth.


Going to keep checking things out. Will report back with any findings.


Cheers,

87_gta

Another update,

After checking and or replacing all the things in my last post. I decided today to check the ignition coil. Resistance in the coil is within spec. I also cheeked my fuel injectors and when cold they were all the 16 Ohms.I also decided today to try and disable the tcc, instead of doing it this time at the brake pedal I decided to get under the car and disconnect right on the trans.

Went on road test and go figure with the TCC disabled it still does it. Only difference is that the car doesn't shake like it did. Engine just has a misfire at 1500ish RPM when in 4th gear. Can feel it slightly in 3rd (drive) as well at same RPM.

Any ideas?

TTOP350

iTrader: (8)

Did you test the pickup coil and icm ?

I noticed you mentioned a custom tune, hows the timing in the affected area? It almost sounds like old carbed cars that need more low end timing when switching to a short runner intake.
Just some things to think about. I know my untuned MR car has chug to it down low in the rpm range.

87_gta

Hi,

No I did not check the pickup coil and ICM. About 4 years ago tho I did replace the entire distributor assembly with new AC Delco unit. (I realize the parts could still be bad). I will probe those.

I do have a new discovery tho.

With my snap on scanner (still leaning how to properly use it) I found you can force the car into limp mode or as the scan tool calls it "Backup fuel" mode.

When that mode is engaged the from what I understand the only sensors used is the coolant temp, TPS and distributor pulse is monitored. The issue also goes away, (car drives like crap in the mode, it will hesitate on hard accel but I would guess thats because a lack of distributor advance) so that tells me that it must be an issue with a sensor???

Any thoughts on what I should look for?

Cheers,

87_gta

Problem solved!

Decided to start adjusting the timing today to get it closer to where it was, rather than the factory spec I put it to while diagnosing this issue.

Adjusted timing to 10 degrees BTDC and the issue has gone away now.

So to sum it up. Car just needed a full tune up. When the issue first started I was running timing higher than 10 degrees BTDC, so it was not just a timing issue this whole while. It just needed more timing again with the mini ram, cam etc.........

Just wanted to post up a conclusion to this whole thing.

Cheers,