Skip to the end of this saga and you will find out that the problem was a badly installed intake manifold generating a vacuum leak....

Recently dropped 383 engine in 1991 base corvette. Complete TPIS intake and headers installed. Can't get engine to run properly. Within 1 degree of timing either the engine will not idle or will not run smoothly after 4500 rpm.

TPIS has been no help. Two GM mechanics have looked at the car. Replaced distributor assembly - no change. The car is at a shop in Wilmington, DE. At the point of deciding whether to trash all of the TPIS intake components and install FAST EFI. Of course installing FAST EFI will require us to basically rewire the whole car to analog and install analog dash.

Need any input regarding tuning TPIS systems. HELP PLEASE!!

Thanks!!

 

Who are you dealing with at TPIS? Jim knows his stuff over there. I suggest speaking with him.

 

I spoke with Jim Hall at TPIS just a short while ago. He has made a commitment to work with my mechanic to get things working. I will report results.

Thank you!!!

 

What TPIS system did you go with? Also, when you change heads and/or engine displacement, you will have to get the ECM retuned and it would be best to dyno tune.

When I just installed heads and cam several years back, I couldn't get the car to start and my tuner burnt a new chip just so I could get it to start and then we got it to the dyno to dial it in.

When I installed the 406, it did start but still had to get it on the dyno.

 

Blueprint 383 with MiniRam with 52mm throttle body. ECM was sent to TPIS. They sent it back with a second ECM that piggy backs on the original. Engine Specs were sent to TPIS for the tune. We have been looking into getting Dyno time.

 

Try adjusting your spark plug gap to .030, I have seen many cars develop a high speed miss after 4500 RPM because the ignition cannot fire the plugs with the higher cylinder pressures after 4500 RPM. Also make sure your alternator is working at 4500 RPM and up. I have also seen alternators quit at high RPM which cause the voltage to drop and a miss to develop. I have seen all of these issues on Corvettes.

You should also be monitoring your AFR since you could be very lean and this could be causing your problem.

 

Thank you sir!!!

 

Did you go with different injectors? If still using stock 24lb, they will not supply enough fuel especially in your higher rpm. And, fuel pump. Did you hook a fuel pressure guage and make sure the fuel pump could keep up with demand?

 

Yes. All new injectors as part of TPIS package and upgraded fuel pump. We will be monitoring fuel pressure.

 

Definitely needs to be tuned. Start with injector offset. Then tune it as you go along. Start with normal driving and idle, then acceleration enrichment, then cranking fuel, then open loop idle AFR depending on how far it changed, then WOT AFR and then lastly timing.

 

Thank you!!

 

Just for your information, I am running a miniram with an ACCEL diff engine management system. All my dashboard functions work except the mpg readout. I wonder if something is wrong with your motor or install. I have found the miniram to be quite forgiving to different tuning parameters.

 

Did you make sure to plug in the EST connector after setting timing and then disconnect the battery for 10 seconds?

 

I'd love more info on your setup and how it's wired. I'm about to add a FAST XFI 2.0 to my '91 Corvette. I gave up on getting the new engine running with the stock EFI (It's either a wiring issue or an ECM problem...time to start fresh).

Jim at TPIS has been good to work with. I'm chasing a problem that doesn't appear to be the prom (coolant temps and other sensors going "full scale" in both directions on occasion, etc...hence the decision to change EFI kits). I'd work with Jim and see if you can save the money and effort of changing systems. I like to tinker so I figured I'd just give it a shot.

If you wind up deciding to go with the FAST system, I hope to have mine done over the winter and I might be in a position to offer some help by then.

 

It's been a long month. We have checked sensors, made adjustments to the idle speed and knock sensor, replaced the 02 sensor (twice), removed the TPIS chip and tried running on the stock chip, changed spark plugs, validated that the electrical/charging system is working properly and validated fuel pressure.

The car runs fine cold but once it warms up and goes closed loop, the computer thinks that the car is running very lean and attempts to feed lots of fuel. The engine then goes rough.

We are switching out the catalytic converter this weekend.

 

I can understand your frustration but there is nothing too serious here. I mean this is just a motor swap which is not that much bigger first of all, second, the intake and headers are not really anything either. Something is not tuned right, or not hooked up right.

Now I have a 1990, which is the same except the body as yours and I put on a Miniram, 32lb injectors, headers (with a leak), and straight pipes no cats with the same cheesy chip that was in it when I bought the car and it started, in fact I had the distributor in wrong and the timing was off and it still started. I mean it was lean as hell and should not be run long like that but it still ran.

This IMO has nothing to do with brand name or whatever. Someone touched something here and has forgotten about it.

-How about Throttle position sensor?
-Did it run like this immediately or after messing with the tune?
-Those changing the distributor are they putting it back in or are they finding TDC and then checking firing order?
-If they are assuming it was right and put it back in the same you will obviously have the same issue.
-Are distributor parts new?
-all things involved here are really the sensors and or parts removed and reinstalled that is more than likely the issue unless a wiring harness or something has been damaged somewhere and not likely IMO.

I am not a tuner at all and know nothing, but from experience I know and common sense about cars tells me this is a plug and play deal with a little dialing in so you need to just relax, take a couple steps back and work with some of the people here that are super knowledgeable. I'll bet if the car ran fine when stopped and motor pulled something is being over looked.
You have a good proven combo there just figure out what the hiccup is.

 

Dont get mad at TPIS. The Miniram is proven to work. I have run the Mini and TPIS headers for years. If you have a big radical cam in there, tuning will be tough. It can make things happen on a MAP car that dont happen with MAF.

 

Great, maybe I'll have to go carb. Mine is a 296/302 .600 lift.

 

I didnt say it cant be done. Its done all the time. I am saying it takes some work to do. Tuning done remote has some drawbacks.

 

Fuel pressure tested?
Vacuum leaks?
Data logs??
No codes?
Even with a 110Cl you can balance out in a tune