I have a MAF TPI setup - it has never really ran well and is very hard to work on for my level of understanding. My friend who is the finest mechanic in my area with all of the tools he can think of gets stumped by this car. Often the car sits for periods of time while we are working trial and error to get the thing to run well.

Bottom line - are there upgrades that will make the car run better and most imprtantly make it easier to troubleshoot? Is going with speed density an upgrade worth considering? How about the Holly commander 950? Other options?

Any info would be appreciated!

By the way, why do my posts have a black dot on the chevy emblem next to my subject?

 

TPI isn't that complicated of a system, it supplies fuel, air and ignition. As far as FI goes it is about the simplest system out there.
If your friend is "the finest mechanic you know", try taking it to a professional....or get another friend

Maybe an explaination of what is wrong with your car would get you some more helpful advice.

 

Well - the problem may be with me. I bought a book on TPI and read it and basically understand it - I have not spent much time as a mechanic though so my abilities are limited as are my tools. I am just wondering if there are ways to improve the stablity of the system and create easier ways to figure out its issues.

At this point it seems like I am going to have to replace all of the sensors and perhaps even the ECM to get the thing run well. If I have to go that far - perhaps upgrades or different systems are in order.

Just replaced the MAF and relays, now the car idles well - something it never did before - but now it cuts out intermittently and feels sluggish. (Please note my earlier posts)

Already replaced the injectors, plug wires, put on adj. fuel regulator. have taken the car to everyone around me that has a shop - nobody can figure anything out.

I read these boards all of the time and have learned a lot but feel I have just scratched the surface - are there more stable alternatives for these cars? It seems they are old enough to antiquated and yet new enough to give efficiency beyond carbrators.

Just trying to figure out how to proceed.

 

What exactly are the issues? Is the motor stock. The more info the better.

The black dot means you have posted in that thread.

 

Be sure to check your fuel filter. This can cause all kinds of problems. If fact if you do not know when it was last changed I would go ahead and change it. Allen

 

monitor your fuel pressure while driving, if it drops off under acceleration the pump may be bad or the filter clogged.
Also, if the oxygen sensor hasn't been replaced that you can confirm, replace it.
If it is cutting out while driving and the pressure is good, start looking at the ignition system, module, reluctor, coils (primary & secondary), timing.
Also, is it throwing any codes?

TPI is a proven and stable injection system and pretty much infinately adjustable.

 

Hey guys thanks for the replies. The car is a low mileage (49,000) L98 engine in a really clean 1987 GTA. Not many mods - SLP headers, flowmaster exhaust, CAI, TPIS fastpack (I know - dumb purchase I was a sucker in the beginning) - new injectors - bosch from TPIS - could be a problem 20lbs - they insisted emphatically that this is what I needed - now not sure about these guys. Also, fan switch and 160 temp t-stat. I am wondering about this too.

Need to check fuel pressure, fuel filter, and someone has suggested ignition issues.

The car cuts out at about really bad at 2500 - 4000 rpm and above 4000 kicks in reall strong. Below 2500 runs fairly smooth now - before the MAF changes it was really rough idle. Even worse before the injector changes. The car after the MAF changes seems to have less power than before - obviously with the powerband failure as mentioned. I really doubt if the car has ever really worked properly and I have no other car to compare it too.

Right now it is not showing any codes. My friend says the computer is too slow to pick up the issues the car has right now. If this is true - the idea of other systems might be in order.

wondering if the TPS is bad also. Perhaps the ECM itself.

 

The oxygen sensor is working fine according to the scanner. In fact all of the sensors are working fine on the scanner. The scanner is a snap on unit.

 

Too slow??? Heh, hardly. If the ECM sees a parameter out of line it will set a code.
You mentioned SLP headers, are you running a 3 wire heated O2 sensor? Really should be with those headers, especially since you are running a 160 thermostat. And don't believe the scanner when it comes to the O2 sensor readings being "right". They may look right, but still be wrong.

As far as the injectors go, is this a 350 or 305? If it is a 305 then the 20# injectors souldn't be a problem (they were 19# stock) If it is a 350, then you've got problems, the 350 prom is set with a 22# injector constant, you'll be running lean.

To check the TPS for a dead spot, disconnect the harness from it and hook an analog ohm meter to the sensor and open & close the throttle smoothly and watch the needle on the meter for any erratic movement. If it does move erraticlly, replace the TPS.

 

I know there is a lot of wishfull thinking out there. But tpi really does suck. Most of the postive respones on TPI are guys who have not yet run into the unsolveable MAF problems. It's only a matter of time for them. My recommendation is do not put a penny more into the MAF set up. Buy a speed density system or holley 950 system and you will be much happier. Maf was garbarge when it was new and even worse when it ages. I also know what you mean on mechanics. I cannot find a mechanic that will even go near a MAF TPI car because they know what a mess they are.

 

Get a grip. I have owned a MAF TPI since it was first concieved (that's 19 years, 7 months now) and there are NO mysterious un-solvable MAF problems. MAF is a very easy and simple system, 2 relays, sensor, wiring and ECM. If that simple of a system stumps people then they had better stick to tinker toys.
I have been through my MAF system from one end to the other, I've replaced the 305 with a 350, replaced the 870 ECM with a 165, burned custom proms for it...there is no big "MAF mystery"
If you can't find a "mechanic" that will work on a MAF system, then their mechanical and troubleshooting ability amounts to chit and should stick to lawn mowers and weedeaters.

And now we are back to the old question....If MAF is such junk, then why did GM go back to it? Why are the ford FI's MAF based?...Because it works and works well.
The holley commander system is a half-assed attempt to copy GM production FI that costs 10 times more and is a royal pain in the *** to set up...and try to get a mechanic to work on it for you if you can. Reccomending that someone pay thousands of dollars to replace an existing FI with aftermarket is nuts.

Oh and BTW, I have been through 1 MAF in the life of this car...it ingested water when it was new (1 week old) and had to be replaced...I am still running the replacement MAF. almost 20 years later.

 

Whoa everybody - We are just trying to learn something here. Morely, you seem like you know what you ar talkng about. For me, it was just a question? When something is hard to solve you start asking questions - there are tons of people running the commander system for a reason. Its guys like you that help us beginners on this forum that keeps us coming back.

Moving on...... I am going to do what you said today if I can - test the fuel pressure under load. I think I can buy a gage that will sit on the windsheld out from underneath the hood while I drive. This way I can tell under lots of condition what is coing on there. Mainly WOT is the problem - which my TPI books says leaves closed loop - but I think the problem might still be there not in WOT and just more stated in the former.

The fuel pump and fuel filter could be the culprits. I have read on here that taking the fuel pressure up to 46lbs is a good decision.
That does not require reprogramming? I do not know what my fuel pressure is - it might be starving for fuel - also the injectors might be too weak.

Regarding iginition - is there a reason why MSD ingition system are so prevelant? Do they help with solving spark issues? We cleared out code 42 tha had been sitting there for awhile which I beleive is for electric spark. Could that be a problem here?

Thanks for the help.

 

Have you pulled the ignition module to get it tested yet? 42 is the EST, did the code pop up again after you cleared it?

 

You have an adjustable regulator but not a pressure guage? Did you use a guage to set it when you put it on? If not then this would be the best first place to look for a problem. At idle you should be looking at 36 PSI, +/- a few psi, key on, engine off it should be around 43 psi. You can set that pressure to 46-48 without a problem. And since you say you have an L98...a 350, those 20# injectors are too small, you need 22#. Try raising the pressure to 48 psi (key on engine off) and have a look at your BLM's in closed loop with your scanner. (post em here)

As for the ignition...MSD is used most because of the price and avialability.

 

Hey guys thanks again for the help here - this is much appreciated. I feel now that I have a path to run on to figure out my issues.

The guys at TPIS said that the BOSCH injectors flowed a lot more than other injectors (Accel) and if I went with bigger ones I would have problems - before I had read more I believed them - they have something like 10,000 race hours so I thought they knew something about this subject - but i am wondering about injector size now. The old ones sat for years with little use so I thought that was the problem with my idle and mild missing issues. The car did run a lot better after the new injectors.

Yes the pressure was set when the regulator was put on - need to look at it again - my mechanic friend did it for my while I was at work and I did not get to see it.

Tomarrow I will check the spark module as well - we are making progress here at least in terms of understanding - the car has to either have a fuel problem or a spark problem - the air is fine with the new MAF and relays.

thanks again for the help

 

I wouldn't trust TPIS as far as I could throw their company.
The injectors that came in the early TPI's were Bosch, so that blows their explaination out of the water.

One word of caution, if you replace the ignition module only use AC Delco or you'll be kicking yourself in the near future.

 

I agree with Morley, I have 200k miles on my MAF TPI setup and only replaced the sensors a couple of times. This is a good , reliable setup and anyone with a basic understanding of it should be able to figure it out.

 

OK - I have looked at my fuel pressure - 36psi at idle. Same key on engine off. Also for some reason - the problems that I was having seem to not be there now. Could the new MAF needed to have a few burnoffs with the new relay being replaced at the same time to start reading correctly?

Well - I decided to call TPIS since they sell the AFPR and ask them how they use them just out of curriosity. They said - that 36psi at idle was way to low and that I could be starving for fuel. Well, we raised it to 42psi at idle - I cannot tell that much of a differnce - the car seems to run better than it ever has - I think relplacing the MAF and MAF relays was a major improvement. The car finally feels stable at idle and at low rpm.

I noticed a picture of a holly unit that had a gage on it. Is it possible to put a gage on the flange that sits on the fuel rail? The one we are using is a snapon unit that is very long so you can read the gage from within the car while we drive - but having one right there on the rail looks cool - easy to read without getting out tools.

I will put the scanner on it tommarow to get readings. What is BLM by the way?

My friend who owns he scanner is really good at using it so I am sure he will be able to tell if it is running rich.

Thanks - any input would be great.

 

Those guages are not meant to be perminantly mounted to the fuel rail. 36 PSI is what the factory regulator is set to...not too low at all. Do a data log wit hthe scanner and see what the BLM's are at in closed loop.

 

My suggestion... If you mechanical skills are not that great. Buy a 2nd gen and start from their. Thats what I did. I bought my 79 Redbird when I was 16 (Still waiting for either the turbocharged 400, or dual quad 400). I worked on that everychance i could. Now I know a lot more and am more resourceful. I'm gonna do the first tune up on my TPI. I know its not gonna be as easy as my 79 since that only had one semi difficult plug, but i can do it now. Trust me it could be worse... you could have an LT1. Yea they go power, but the optispark always goes and a cap and rotor is $180.

Code 42: Electronic Spark Timing (EST) circut - open or shorted to ground during engine run.

 

Did you test all of the relays and the MAF sensor before replacing them? Becoming a part swapper is NOT how to get into this business (even just for your own recreation).

 

I did not test the maf or the relays - actually not sure I know how to test them - this is the first time I have heard this or seen this on this forum. It does make sense though - I have questioned the possiblity of the parts being defective but have not known how to verify that. I guess a volt meter would do the trick on the testing?

 

Ok, I read thru this thread real fast,, as usual Morley has alot of good stuff above.

I got one point to make that was touch on above. It was said that the injectors are 20# and its a 350. Yes, the ECM is programmed in the constants table for 22# injectors. You have an AFPR. So, For a 20# injector to flow like a 22# injector the fuel pressure must be about 53psi. This fuel pressure is set with the engine idleing and disconnecting the vacuum tube from the AFPR and plugging it. OR you could turn the key to the on position (do not start engine) and instantly read the peak fuel pressure reach. You need two people to do this because you dont have time to get out of the drivers seat and read the fuel pressure usually.

edit: Factory fuel pressure is about 44psi.

And as stated above check the fuel pressure under WOT conditions. it should stay up where it is set.

BTW: My 1987 350 IROCZ started to stumble under hard accel. I changed the fuel filter, no more problem. This was about 7 years ago, so the car was 10 years old then with the original factory fuel filter.

 

Hey guys thanks for the info - it is raining cats and dogs here today so I could not take the car out to get BLM readings.

The reason I have 20lbs injectors is because of not knowing enough when I bought them. Yesterday I talked to TPIS and asked them why they sold me these smaller injectors. They said it was because flow rates have changed since 1987 and today's 20lbs injectors flow like the 22lbs injectors of the 80s. Has anybody ever heard of this? I am thinking of buying accel injectors and selling these - might even try to get TPIS to take them back and sell me bigger ones.

For some reason - the fuel pressure with key on engine off was not any higher than my car at idle. At WOT the psi got up to the mid forties with the pressure at 36psi at idle. Have not yet checked it since I raised the psi to 42 under load. Does this sound correct?

 

Subscribing to a kick-*** info thread. :lala:

 

OK, the pressures are good for stock...but as you said you don't have stock injectors and you really don't want to try running the stock pump at 53 psi to make up the difference.

So, now you need injectors... you can go with these http://www.slponline.com/view_product.asp?P=23051 But you'll need a prom chip burned for a 25# injector constant. If you are strapped for cash or can't do the prom thing, I have a set of 8 stock 22# injectors I removed from my 91 Formula. They are Multec injectors and are not the best choice that GM made for injectors. They do work, I replaced them because they were Multec's, they will need new O rings (I may have a set or two of them too) but, as I said, they do work and are the proper size for your engine and will do until you can get better ones.
I'm not "selling" them, I'm offering to give them to you, just let me know where to send them.

 

Hey everyone,

Thanks for the friendly and helpful advice. Still raining massively here - cant drive the car yet. I am going to call TPIS today and see if I can work something out with them in terms of jumping up to different injectors by sending the ones I bought from them back. They probably will not do it but I want to try that first. I will have to check the scanner first to prove the small injector issue I am sure.

Thank you Morely for your help here - very appreciated. I checked out the SLP site you attached - the injectors seem to cost $99. That sure does seem low since the Bocsh I bought from TPIS were a lot more than that? If that is the case - I can afford it - no problems and get a chip also.

Regarding getting the prom reprogrammed - either Fast Chips (Ed Wright) or get the stuff and learn it myself - then again I will need a lot of help there too.

It sounds like I can leave the fuel pressure where it is. We are making progress!

 

Well it has been a while since I asked for help so I wanted to update what happened here for anyone that read this or reads it in the future.

As it turns out, the O2 sensor was bad. We ended up taking out the distirbuter and the pickup coil was corroded so we replaced that and we replaced the spark module but that fixed nothing.

We noticed on the scanner that the O2 sensor was not reading very wide numbers and that the car took longer and longer to go into closed loop. Thinking that the O2 sensor was going bad we decided to replace that and it was fixed.

The car finally runs like I have wanted it to from the time I bought it - a year of frustration finally coming to an end at least for this time around.

One reason to explain the O2 sensor - last year when I put the car away for the winter I unwisely put a fuel stablizer to keep the gas from getting old as the car would sit for several months. As it turns out, my friend who did the exact same thing with the same product - his O2 sensor went bad too. Not totally sure but this is the way it came out. I took mine longer to go because I do not drive my car that much.

I wanted to say thanks for the help for all those who commented with good insight and ideas.

Tom

 

From what I understand, all a fuel stabilizer does is absorb moisture. Some dry gas, or STP Gas Treatment would do the same thing, and won't harm your sensors.

Also, run your tank as low as you can before you park it and then when you run it again, fill the tank with fresh gas. Gasoline is a great solvent, and the little residual fuel you have left will be diluted.

Again, great info. I'm glad I stumbled on this post. It's nice to find one thread with intelligent content

 

Excellent idea. I did not think of running the gas low before parking the car for the winter. As for the additive - I am not sure it ruined the sensor - all I know is that my friends 02 went out quickly afterwards and mine did evenatually. Thanks for the comments though.