I just found out that the 91 RS I bought doesn't have the original 305 but actually has a truck 350 with my original TBI on top. I have read on here that I need to swap the ESC module for the 350 to run as well as it should. Incidentally, it was a SES that threw a code for the ESC being shot that led me to discover that a had the 350, so it needs changed anyway.

Anyway, my parts store can't find the ESC for the 350. Does anybody have a part number or a source?

Since I'm changing this anyway, is there anything that I should upgrade to? I read that the 305 ESC was "less aggressive" than the 350 ESC, so if there's something more aggressive than the 350 module out there, maybe I should go to it? Serious mods on the horizon. Don't care about mpg.

Thanks

 

The TBI and TPI modules (regardless of engine size) should be all the same. For example the Niehof brand uses part number DR411CS.

Hope this helps.
Lou

 

So that would mean that as long as I still have the TBI unit I don't need to change anything? I read on the tbichips.com website that they were calibrated for engine size so the L05 (TBI 350) had a different one than the L03.

BTW thanks for the help a while back with the connector diagrams for the instrument cluster. Those were majorly helpful.

 

No problem, glad I could help.

I went to a car parts website and looked up the ignition module for my car. Then I changed the vehicle to a 1991 350TBI Suburban and the part numbers didn't change so that confirmed it for me.

A spark doesn't usually care about the displacement of a cylinder or the way the fuel mixture gets there so the modules should be even logically identical for all later fuel injected thirdgens.

Lou

 

Thanks Lou. Just to confirm though, I have already had some confusion when talking to my parts store. You referred to it as the ignition module.

This is not the ignition module that sits on the back of the distributor, this is the black, flat plastic chip-like thing on the firewall-drivers side in my car.
Sometimes referred to as EST (Electronic spark timing module)
Someone just explained to me earlier this week what it does, but its been a long day and I'm at a loss to explain it right now. i believe it has something to do with digitally controlling the spark timing.

 

ESC = Electronic Spark Control - this module, along with the knock sensor, sends knock signals to the ECM which responds by retarding the timing when knock is encountered. ESC is not to be confused with:

EST = Electronic Spark Timing - this module located inside the distributor, receives timing signals from the ECM and adjusts the timing accordingly.

 

Oh, I see, I did not know that because all the TBI's and TPI's have an EST module in the distributor, so I assumed that's what you were talking about.

So when they put in the 350 truck engine, they put in a the truck computer and wiring as well? In that case, you'd need to go to the store and get the ESC module for that year truck without telling them what car it's in currently.

Lou

 

Ok, let me see if I am starting to understand this right:

There is an EST module in the distributor. This is something different than the ignition module, right? And the EST is the same regardless of engine size?

The ESC is the small black square on the firewall. Information in another post tells me that it does need to be changed for the 350.

Is all that correct?

Here's the only problem that is left. I paid a guy that knows a lot about the electronics on these cars to check it out. He told me that the EST was bad, but he pointed to the one on the firewall, which I understand to be the ESC.

Anybody got ideas for how I should proceed?

 

Oh, BTW to answer your other question I don't know if they put in the 350 truck computer.

I am currently investigating that. I really doubt it because nothing else appears to be swapped. For example, I had the wrong timing tab to match my balancer. This was the cause of two days frustrating efforts to get the car timed and runnning. We finally figured out what was up with the timing mark, which is when we checked the casting number and realized it was a 350. After we finally got it timed I had the SES code for the EST. The aforementioned guy was able to confirm it was bad (don't ask me what he did). The car runs smooth but seems lacking on power for a 350 so I think it may be the computer, ESC or a combination of both.

As for the computer, if I am going to get a chip burned anyway, do I need to replace the computer or just get a more appropriate tune? Sorry to write a novel here.

 

The EST module is often called the ignition module. They are the same for 305 and 350.

Well. . .there are two different types of ESC modules. There is an external module which is located on the driver's side of the firewall. There is also an internal module that is located inside the MEMCAL inside the ECM (computer). Which is used depends on the ECM used.

Do you NEED a 350 specific ESC module--no. Having the correct one would likely give you better knock retard which could save your engine from the destructive effects of detonation, then again the wrong module might actually provide greater protection but at the expense of performance.

Step one: find a different mechanic/electronics guru.

 

The ESC is engine specific, its on the firewall as you correctly stated, i just switched my 305 one for a 350 one, ill grab a part number for you in a few if you need it. The ESC however should only be changed if you change to a 350 knock sensor which is engine specific also.

The Ignition module might need to be changed, i did a swap and mine is causing me some problems

as far as the chip, pull the numbers off your computer, Third gens had specific computers while trucks had different ones the numbers will tell you which one you have and what kind of chip you will need

 

Unfortunately its been an adventure finding a halway competent mechanic around here to begin with, let alone finding somebody who knows third gen electronics. Thats somewhat beside the point but this guys has done some pretty impressive electronic trobleshooting for me before and he is the one who solved the timing tab issue. That said he told me that he verified that I had the correct 350 knock sensor and he is the one who solved the timing tab issue. I feel pretty confident he knows what he taling about on the knock sensor so I am going to assume it is the right one.

 

I found the two different ESC modules on autozone.com.

Did you gain any performance by changing your ESC?

So it seems that I have a 350 engine with a 350 knock sensor and presumably a 305 computer (still to be verified). I guess I will try the 350 ESC and see what it does. baseed on the post above saying that there is another part of the ESC system in the MEMCAL, I don't know if I should stick with the 305 module or not.

I'm definitely going to pull the numbers off the computer. It'll probaly be at least this weekend before I can get to it. I'll pull the ignition module while I'm at it and get it tested.

 

ESCs and knock sensors work together, its quite possible you have a 350 knock sensor and a 305 ESC

No performance gains the ESC simply controls retarding and advancing timing based upon reading from the knock sensor

 

I wonder though if having it mismatched might be causing it to improperly adjust the timing, leading to inefficiency.

 

Im not an expert but from what i can gather I would assume that that could be the cause of your problem, unless its failed altogether, although you dont know what kind of knock sensor you have either so your better off changing that and putting in a 350 ESC also, the guys at advance looked at me like i was stupid when i asked for an ESC and they are pretty pricey from them. A knock sensor is 40 and an ESC is about 80.

Its a pretty easy job, you have to drain the coolant and such and it took me about an hour this past weekend to do.

 

Any way to tell which knock sensor I have?

The guys at O'riely here looked at me like they'd never heard of an ESC too.