Maverick13

Since swapping the 305 for a 350 (using same intake, plenum, injectors, prom, adding fuel pressure regulator, new fuel pump) and swapping the T5 for a Tremec 3550/TKO, I've noticed jerking at certain RPMs (usually between 1600-2100).

The mechanics claim it's either one of two things (though both are fuel related):
<DD>the computer shows the O2 and EGR going back and forth between rich and lean (and ultimately going lean due to EGR at around 1600 and 2100 RPMs).
<DD>the prom is for a 305 and it not delivering enough fuel to the engine and causing it to run lean

The problem is that after the swap, money is very tight (I already had to dish out $$ for a new flywheel because I found out when I had my clutch done 1.5 years ago, the machine shop gave my mechanic the wrong flywheel (v6!!) and he failed to notice.. anyway, when the 350 was put in, the v6 flywheel was way too small for it and caused big problems), and I really don't have money for both of these right now. Which is the better investment/better bet for fixing the problem?

Whether I get the software and tools to burn my own prom or get a Superchip "custom burned" for my application, I'm looking at $400-500 easy. The EGR is like $30 in parts, but costly in labor (due to GMs bright idea of burying the thing under the plenum). I've tried removing the plenum, but I really don't know where to start, and my Chilton manual is vague on the subject (suggesting I remove the intake, fuel rails, runners, everything.. which I do not feel comfortable doing on my own since I'm a novice at engine work).

Ultimately I'll get a new prom (preferably one I make myself), new injectors, when money is less tight. But for now, I just need to get the car back to running smoothly.

Any help is greatly appreciated. Thanks in advance.




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Maverick
1989 Formula 350 TPI
5spd Tremec 3550/TKO
several suspension mods

Vader

Mav,

There should be a fairly reasonable solution to your problems that won't cost you any useful extremities.

I would suggest that you replace the EGR valve yourself. Once the plenum is removed, there is nothing else to move out of the way. Do yourself a favor, however. Avoid the generic replacement EGR valves and get an OEM AC/Delco EGR valve. You'll have a lot less trouble overall, and you already have a "bastard" engine with a lot of variables. You don't need to throw in another wildcard with an EGR valve that might just barely operate correctly on a stock engine. Get the correct AC/Delco valve for a 350 TPI (NOT the 305).

You can remove the plenum by loosening all the upper and lower intake runner tube bolts, then lifting the plenum up and out of the way. You'll probably have to disconnect the throttle cables and some of the vacuum hoses for the FPR and HVAC system, but little else.

Check this for a visual description:


There are a few things you should have if you don't already. Get a good quality Torx bit to remove the runner bolts. A generic "Pacific rim" brand will only fail and cause damage to the bolt recesses, frustrating you beyond description. Use plenty of penetrating oil before disassembling anything, and oil up a couple of days in advance, and a few times before the project starts. Plan to allow a full day or weekend to do the job, just in case you encounter a larger problem. Use new gaskets on the plenum (about $30.00 for a Fel Pro set). When you reassemble, use anti-seize on the fasteners to allow you to remove them in the future with ease. While the plenum is off, thoroughly inspect the vacuum hoses.

The EGR valve is located right here, and as you can see, the runners don't have to be completely removed. The fuel rails can stay on as well, but they were removed here for injector access.


As for the fuel delivery problem, you already have two stikes against you. The injectors are sized for a 305 (19 lb/hr flow rates) and the PROM thinks it should deliver fuel to a 305. Even a 350 PROM would be better than nothing. The best answer would be a set of injectors and a PROM, but get the PROM for sure. If you ask nicely on the PROM board, you might find someone willing to part with their unused original PROM, or burn a "reserve backup" PROM on a chip you provide. That should be worth sending a twelve-pack or so, and is a lot cheaper than the $52.00 you'll pay a dealer parts department for a new original PROM.

If you undertake the project yourself, you might want to plan an injector swap in conjunction with the EGR replacement. The money you would have spent for your mechanic to replace the EGR can probably buy a set of 24 lb/hr injectors, or at least some 22's. Get your hands on a PROM for $50.00 or less, and you'll be done for the cost of the "easy way" of doing the EGR valve.

Just a suggestion. If you want to tackle it (it's not that tough) I have some instructions that might be useful.


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Later,
Vader
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"What a Day..."
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Maverick13

Vader -

Thanks a bunch. Your reply raises a few questions though. Will a stock 350 PROM work okay considering the Formula is a 5-speed and stock 350s are automatics (wouldn't it send off codes?)? Also could I use stock injectors off of a 350 from a boneyard, or should I just stick with a set from Jegs?

Lastly, if you could please or send the instructions on installing the injectors, I'd like to see them. Chilton has some, but I'd like to cross reference. Thanks.



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Maverick
1989 Formula 350 TPI
5spd Tremec 3550/TKO
several suspension mods