Old Blue - 1984 XL Flareside

[ckuske]

Honestly, to me that seems like it's just the convertor starting to load the engine.

While the engine may become a little 'rough' it's ultimately a carbureted engine hobbled by 39 year old emissions standards.

Do you actually drive it that way?

I don't want to sound dismissive, I'm just trying to understand. 🙂

Jim,

No worries! I understand.

I get it is a different vehicle than my drive-by-wire turbo Accord. I agree where you are coming from. The roughness is ok.

It’s not in the video because sometimes it is worse than others, but if I hold the throttle there, I can stall the engine semi-reliably.

Basically, I don’t want to risk stalling because I didn’t punch it when trying to gently pull away from a stop.

And it’s not really about me as much but my son. He’s wanting to drive the truck, but he’s 16 and I don’t want him stalling it in traffic etc (if I can help it)

This is all more about optimization and striving for that last one or two percent making it as good as I can.

[ArdWrknTrk]

Jim,

No worries! I understand.

I get it is a different vehicle than my drive-by-wire turbo Accord. I agree where you are coming from. The roughness is ok.

It’s not in the video because sometimes it is worse than others, but if I hold the throttle there, I can stall the engine semi-reliably.

Basically, I don’t want to risk stalling because I didn’t punch it when trying to gently pull away from a stop.

And it’s not really about me as much but my son. He’s wanting to drive the truck, but he’s 16 and I don’t want him stalling it in traffic etc (if I can help it)

This is all more about optimization and striving for that last one or two percent making it as good as I can.

Im very much a shadetree mechanic and have never liked driving automatics (except in stop & go traffic)

If it were a drag car with a C6 bogging out of the hole I would say change the converter for one with a higher stall, but this is a street vehicle with an AOD so linkage adjustment is critical to longevity and I wouldn't mess with adjustment.

.... Mostly because I know I could do more harm than good.

It might be worth checking the TV rod for proper adjustment.

I can only assume that it's been off and on a bunch of times if you've been working on the carburetor.

If I'm way off base hopefully someone like Bill will correct me.

[85lebaront2]

Jim,

No worries! I understand.

I get it is a different vehicle than my drive-by-wire turbo Accord. I agree where you are coming from. The roughness is ok.

It’s not in the video because sometimes it is worse than others, but if I hold the throttle there, I can stall the engine semi-reliably.

Basically, I don’t want to risk stalling because I didn’t punch it when trying to gently pull away from a stop.

And it’s not really about me as much but my son. He’s wanting to drive the truck, but he’s 16 and I don’t want him stalling it in traffic etc (if I can help it)

This is all more about optimization and striving for that last one or two percent making it as good as I can.

Back to something else I mentioned earlier, EGR valve, if it opens too far as the throttle is opened, it will cause a severe lean condition, to the point of probably stalling the engine. It will be more noticeable on easy throttle opening as the accelerator pump shot is very slight under those conditions.

Your EGR control system is the same style that was used through the 1986 302 engines, there are two solenoid valves, a vacuum and a vent and they control the EGR by alternating to open it the desired amount. I imagine it is the same criteria the 1985/86 EFI 302s use, somewhere around 1.05-1.10 volts on the TPS sensor, the EEC commands the EGR to open, assuming the other criteria (engine temp etc. are met) the EGR solenoids may chatter when this occurs as they are balancing the EEC command against the EGR position sensor signal. EGR position is called EVP for Egr Valve Position and is a 1-5 volt range.

I would try disconnection the EGR vacuum hose, plug it and repeat the light throttle test. If the engine comes up smoothly, then the EGR system is the culprit. Check the EGR vent valve filter, if it is dirty and maybe clogged it will not release the vacuum quickly when the vent solenoid opens.

[ckuske]

Back to something else I mentioned earlier, EGR valve, if it opens too far as the throttle is opened, it will cause a severe lean condition, to the point of probably stalling the engine. It will be more noticeable on easy throttle opening as the accelerator pump shot is very slight under those conditions.

Your EGR control system is the same style that was used through the 1986 302 engines, there are two solenoid valves, a vacuum and a vent and they control the EGR by alternating to open it the desired amount. I imagine it is the same criteria the 1985/86 EFI 302s use, somewhere around 1.05-1.10 volts on the TPS sensor, the EEC commands the EGR to open, assuming the other criteria (engine temp etc. are met) the EGR solenoids may chatter when this occurs as they are balancing the EEC command against the EGR position sensor signal. EGR position is called EVP for Egr Valve Position and is a 1-5 volt range.

I would try disconnection the EGR vacuum hose, plug it and repeat the light throttle test. If the engine comes up smoothly, then the EGR system is the culprit. Check the EGR vent valve filter, if it is dirty and maybe clogged it will not release the vacuum quickly when the vent solenoid opens.

Thanks Bill, I tried that awhile back, but that was before I fixed a couple of the vacuum leaks. I will try that again. I feel there are multiple variables in play.

Regarding what Jim said about the TV rod - I did measure the pressure and it is higher than it should be in park. It's around 15PSI if I recall correctly.

With Jim's comment about the torque converter engaging being the potential source of the change in sound/rougher idle, could that be a potential cause of the overall behavior?

It's on my list to take it to a transmission shop and get it adjusted at the transmission itself. The screw on the carb is basically backed all the way out already.

[ArdWrknTrk]

Thanks Bill, I tried that awhile back, but that was before I fixed a couple of the vacuum leaks. I will try that again. I feel there are multiple variables in play.

Regarding what Jim said about the TV rod - I did measure the pressure and it is higher than it should be in park. It's around 15PSI if I recall correctly.

With Jim's comment about the torque converter engaging being the potential source of the change in sound/rougher idle, could that be a potential cause of the overall behavior?

It's on my list to take it to a transmission shop and get it adjusted at the transmission itself. The screw on the carb is basically backed all the way out already.

I only meant to say that the roughness seems to occur as the torque converter starts to load the engine.

Definitely understand what you say about multiple variables.

I also disagree with your carburetor guy being dismissive of EGR. It has its purpose and was perhaps the only solution available to the auto industry at the time.

Taking it out of the equation (for testing) could prove helpful.

I don't really know if this stumble is due to fuel mixture, timing, weak spark or whatever...

[mat in tn]

Honestly, to me that seems like it's just the convertor starting to load the engine.

While the engine may become a little 'rough' it's ultimately a carbureted engine hobbled by 39 year old emissions standards.

Do you actually drive it that way?

I don't want to sound dismissive, I'm just trying to understand. 🙂

having checked as much as possible so far. I like the earlier suggestion about the timing chain test. I usually consider them worn out by 150k (my own decision based on my results). even when I replace with a good double roller I can still find more slack then I like at 150k. I have had many ask why I do this if it's still "running good". because I want it to keep running good! I put a lot of miles on some of these trucks/vans. one I put 408k on a 5.0 that only got timing chains and plugs/wires. do you have an idea of the mileage on your engine? it can be hard with the odometers in these trucks. after 100k it's a guess or an honesty issue. I find "low mileage" trucks every day. "original miles" even:nabble_laughing-25-x-25_orig:

[ckuske]

having checked as much as possible so far. I like the earlier suggestion about the timing chain test. I usually consider them worn out by 150k (my own decision based on my results). even when I replace with a good double roller I can still find more slack then I like at 150k. I have had many ask why I do this if it's still "running good". because I want it to keep running good! I put a lot of miles on some of these trucks/vans. one I put 408k on a 5.0 that only got timing chains and plugs/wires. do you have an idea of the mileage on your engine? it can be hard with the odometers in these trucks. after 100k it's a guess or an honesty issue. I find "low mileage" trucks every day. "original miles" even:nabble_laughing-25-x-25_orig:

Thanks Mat, yep, that one is on the list to do. I worked on the interior this weekend, it is nearly done. I'll post pictures hopefully next weekend.

The truck has 308000 miles on it total, but the engine was rebuilt at 265000, so since the rebuild it has ~43000 miles. Hopefully the test comes out OK - I'll be kind of upset if it doesn't!

Chris

[mat in tn]

Thanks Mat, yep, that one is on the list to do. I worked on the interior this weekend, it is nearly done. I'll post pictures hopefully next weekend.

The truck has 308000 miles on it total, but the engine was rebuilt at 265000, so since the rebuild it has ~43000 miles. Hopefully the test comes out OK - I'll be kind of upset if it doesn't!

Chris

if you find excess slack at 43k then something aint right. But if the test shows slack, then it is what it is. replace the chain.

[ckuske]

if you find excess slack at 43k then something aint right. But if the test shows slack, then it is what it is. replace the chain.

I'm way overdue on replying after doing the timing chain test. I'm still going to do it, but after stepping away from the problem, I am almost thinking it isn't an engine problem at all. I mean it still can be I suppose, but hear me out:

This behavior only happens when the truck is in gear. In park or neutral, I can rev it all day with ZERO stumble/hesitation.

Could something be wrong with the transmission, or more specifically the torque converter? When it engages, perhaps it's engaging too early etc? The shift behavior is good, smooth, etc. But the "only in drive" thing seems like a clue.

Just a thought. I'll post project updates in another post...

[ArdWrknTrk]

I'm way overdue on replying after doing the timing chain test. I'm still going to do it, but after stepping away from the problem, I am almost thinking it isn't an engine problem at all. I mean it still can be I suppose, but hear me out:

This behavior only happens when the truck is in gear. In park or neutral, I can rev it all day with ZERO stumble/hesitation.

Could something be wrong with the transmission, or more specifically the torque converter? When it engages, perhaps it's engaging too early etc? The shift behavior is good, smooth, etc. But the "only in drive" thing seems like a clue.

Just a thought. I'll post project updates in another post...

Testing for timing chain slack/slap takes 5 min and a single tool (deep 15/16 on a breaker bar)

Diagnosis is about methodically eliminating potential problems (at least without something like OBD-II)

Before fretting about an inaccessible thing like the torque converter maybe do the test in less time than you've devoted considering the fluid coupling?