I live in Chicago so I have to deal with this emissions crap. What makes things worse is that I have a '91 Camaro that I had the engine switched from the stock 305 to a 350. The bad part is that they switched to the 350 block and left the 305 induction on the engine (also presumably the 305 computer and whatever components are different). The engine runs reasonably right now despite an occasional stall, but I do have a few concerns:

1. What components are currenly mismatched? If I have a 350 block- I think it'd be smart to have all 350 components. I wouldn't mind switching from TBI to carbureator or some alternative, but:

2. I have to pass emissions by the end of the month or the sec. of state will suspend the liscense. Last test it failed due to too much fuel in the exhaust (from memory- I think that was the problem) Will a simple tune up fix this or will I need some new stuff?

Regarding the mismatched thing- this is because I paid too little for the work Of course nobody knows exactly what's mismatched, but assuming a 305 to begin with what parts differ on the 350 setup?

Thanks for any help!
-Kevin
Thanks for any help!

 

Kevin, is this a TBI set up or TPI? Since you just said Camaro and not Z28 I'm assuming a TBI RS.
I understand you will need to upgrade the ECM since it is set for the much weaker flow characteristics of the 305/Heads. Like you said, the engine runs, it could just run much better (45cu of displacement). Hopefully the experts will jump in since I'm no expert by any means!
As for the emissions stuff, it should work the same on the 350. Both are basic small block chevy motors.

 

Switching to carb is definately not the answer, since carbs weren't offered in '91, and you can't go backwards.

Most likely, you failed last time for excessive hydrocarbons, which is possibly caused by an excessively rich mixture. The O2 sensor can cause that, and since they only cost around $25, is a good place to start. A thorough tune-up (plugs at least, set timing correctly) will also help. Leaking fuel injectors can enrichen the mix, so run some cleaner through the tank before you go for the test. A fresh oil change can also lower hydrocarbons. If the 305 was spitting oil out the exhaust, you may have also fried your catalytic converter.

Try those basic things before assuming it's something complicated. There is no particular reason 305 parts are "mismatched" with a 350 for the purposes of emissions.

 

This is a TBI setup. Are the computers for the 305 and 350 the same except for the eprom programming? I would like to change the chip to erase the speed limiter setting, so if the computers are the same- then maybe I just need to swap the chip...? I had posted this same question a while back and more than one person suggested going to carburation. Now I'm in a bind because something failed today- for the first time ever. It was very strange, but it just seemed to spontaneously fail, and now won't start at all. I had just a slight bit of warning, about 10 miles and 15 minutes of driving earlier, it had trouble starting and was not wanting to run. I took out the air filter, and pulled the throttle linkage by hand- no fuel to the TBI. I'm thinking this is the fuel pump. So now I'm reading up on what it takes to change that (since I have no job and barely any money left).
Getting back to my original question: I know that the carbureator engines used a mechanical fuel pump mounted to the block. I know it's crazy- but if I converted to carbs now, could I use this same mechanical pump? Easier than my replacing the electric pump? Thanks for any replies- and please reply soon since I need to make this happen right away!
-Kevin

 

Kevin,

The two ECMs are virtually the same, with the exception of the EPROM. The injectors for the 350 were probably larger, but that isn't your problem right now.

Converting to a mechanical fuel pump probably isn't the answer, and may not even be possible depending on what 350 was installed. On later 350 EFI engines, the factory camshaft didn't even have a fuel pump eccentric machined onto it - just a series of indexed mill cuts to provide clearaince at the cam bearings when installing. If the block was drilled for a fuel pump rod, and you changed camshafts, you might be able to get away with it. Or not. The one on top in the photo is an orignal GM roller cam:



The fastest, cheapest, and easiest solution is to get the ECM back in control of the engine, pass the sniffer, then work on whatever other issues you may have. I know from experience that low fuel pressure will make a TBI run rich in open-loop mode. A weak oxygen sensor will make it just as bad in closed-loop mode. You need to have a good cat converter, a working A.I.R. system, a good oxygen sensor, and a good fuel filter. The coolant temperature sensor needs to be functioning as well. If everything is working correctly, the engine will likely be more lean than rich, and should pass on HCs but may be high on NOx from the lean combustion and resultant high temperatures. Because of this, a functioning EGR system will be necessary. I hope for your sake the people doing the conversion reinstalled all the necessary parts.

You'll need to have or borrow a DMM to test a few items, and a fuel pressure gauge and adapter might be handy as well. Test the fuel pressure first, then get back with results.

 

That is strange- I'd expect a lean mixture with low fuel pressure. I wonder why the opposite occurs... I didn't think a mechanical pump would be the solution, just a crazy idea I had opposed to the dreaded thought of chaging out the pump that's inside the gas tank. This is not going to be a fun job.

Is everyone agreed that this problem sounds like a physically faulty fuel pump? If it was electrical, I don't think I would have gotten any notice, and if it was something else, it probably would try to run at least a little. And no fuel at the TBI is a good indicator I think as well. Still most of my experience comes from working on my 302 mustang engine so I thought I'd double check with my new camaro family.

I have the tools to reprogram the chip, but I would like to find out where I can get the eprom programming for a stock 350 engine (or stock minus the speed limit) so I can upload it to the chip.

It's raining in Chicago today, so I wasn't inspired to go fix it especially since I will have to be working outside....
Thanks for the help, keep it coming!
-Kevin

 

You'll be looking for a long time No 350's were offered in F-bodies with TBI.

Could look at the Caprice and Truck TBI'ed 350's for some starting programs, but I know there many differences that do not allow you to simply plug in those EPROMs into your ECM.

I know one person whose made the swap from 305 to 350 TBI and ran the 305 EPROM, only change was to 350 TBI truck injectors, increased the timing a bit (may not pass emissions with increased timing over "305 specs") and adjusted fuel pressure.

Car ran very well ('92-94?? Caprice crate engine), all info on my scans at idle and WOT runs looked well, don't see any reason why it wouldn't pass Ca Emissions as a 305.

P.S. You're not planning on telling them (smoggies) it's a 350, right?

 

What do you think they would say (smoggies) if I told them it was a 350 block? I don't know how they handle stuff like that. I tried to make some updates when I first got the engine switched, including increasing the fuel pressure using a tip I got from this forum, that is- drilling the TBI and allowing the regulator to be adjusted with a screwdriver. Still, I guess I would need to find an injector from a caprice or truck to get it right. I'm surprised that there aren't more differences between the 305 and 350. Especially since the parts you order for each engine are normally different. I never know which to order.
thanks for the help!

 

i am pretty sure my friend had an 87 iroc with a tbi 350. blue, t-tops, auto, yada, yada; it also got totaled in chicago.

as for the emissions, i talked to the guys at the emissions testing station (WI) about going to a 350. they said i could get my engine size registration changed with the dmv so i would get tested at the 350 level and not the 305.
Jess

 

Thats a really good point! since i now have 350ci of displacement, i should be expected to have a proportional increase in emissions I would think. I suppose I'll have to call up the DMV and see what they have to say about that.

As for the 350/tbi combination, I had heard that they didn't do that for that year except on the trucks and caprice- in fact, they didn't offer a 350 at all for any '91's with T-tops (like mine has). So it's definately a one of a kind.
thanks!
-Kevin

 

Just wanted to retract this point. It's not such a good point after all, not in illinois at least, according to the guy at my emissions test place, it's illegal to switch engines to anything other than that which came with the car. However it seems this is open to interpretation- and maybe it's different for wisconsin. In any case, he certainly didn't seem convinved that there was any way to change registration to the higher displacement engine I now have. So my advice is to avoid asking this question. I'm glad I got out without getting myself in more trouble.
-Kevin

 

Kevin,

There's no doubt about it - it's definitely different in Wisonsin. Badgers, Packers, no toll booths, fresh beer, 14,000 lakes (two of them great), real butter and cheese, trees without beetles, good sauerbraten, concrete instead of asphalt. etc. As for the emissions standards, there are some differences too.

You have to meet the emissions standards for a 1991 'F' car. In this case, size doesn't matter. Your 350 should easily be able to blow the sniffer at the same rate as a 305.

As for testing the O² sensor, you can test it with a voltmeter, (digital, on a 2V scale). Once the exhaust is up to temperature, the sensor should be reporting a voltage between 300-700mV and varying. Another way to test it is to remove it, connect a voltmeter, and expose the tip of the sensor to the flame of a propane torch. Propane burns very completely and cleanly, and should produce a high reading. The sensor should produce a 750-800mV signal within a minute. Removing the sensor tip from the flame should drop the voltage to less than 100mV within a few seconds. If it take smore than five seconds to drop to this level, the sensor is sluggish, and is probably contaminated.

If your sensor is good, test fuel pressure. Low fuel pressure can cause rich operation on a TBI (or any speed/density control scheme) due to the very poor atomization of fuel from the injector tips. Liquid fuel can dribble or stream out of the injectors instead of creating a fine spray mist. This liquid fuel can wet the intake, throttle body, and eventually cause a ricj mixture as the engine warms up and the fuel evaporates.

Timing will be critical as well. Excessively retarded timing will result in incomplete combustion and higher HC output. Excessively advanced timing can result in higher combustion temperatures and NOx readings. Set up you engine just like it was the 305 TBI and size the injectors accordingly, and it should run well.

But first verify the O² function, fuel pressure betweem 11-13 PSIG, and EGR operation.

We need to get some data on the car.

 

Kevin,

Another thing that was mentioned by 5-7 is the ignition system. You MUST have a reliable ignition system that doesn't misfire. A single spark plug that misfires once in every three cycles can easily increase HC emissions by 10% in a V-8 engine. If your spark plugs and wires aren't reliable, they need some attention. The same goes for the cap and rotor, coil, etc.

So, what have you done with it to this point?