Im having a few problems with my 85 (F Model) 5.0 TPi Trans-am , it will start every time and runs but quite often has a bad misfire/flat spot low down or when you floor it there is a lack of power , also the idle fluctuates at times sometimes sitting steady at 700-800 rpm , other times holding at 1400-1500 rpm and sometimes down to 300-400 rpm , I was going to replace the ECU and MAF sensor and MAF sensor burn off relay (which I am told is unique only to the 85 TPi cars)and the TPS switch , I may also try changing the timing control relay (beside the brake servo). Can anyone help me to find these parts at a reasonable price or offer any other suggestions to cure the problem , as I said the car does drive so its not a panic but I would just like to get it running correctly.When I bought the car it had all the engine sensors changed (All 8 injectors/knock sensor/MAF(remanufactured)/ECT/EGRValve/EGT/TPS/O2/IAT/Cold Start Valve/Fuel pump and filter)so I reckon the guy I bought it from was trying to sort this out and could'nt.
Thanks
Daron

 

Save yourself a couple of hundred dollars, and don't buy any of the things you mentioned. You more than likely will not fix your problem with any of those items. Instead, borrow a scantool (or preferably, buy a $30 ALDL cable, download TunerPro RT, and borrow a laptop from a buddy). Using that, you can take a look at what the ECM is doing, and what all the sensors are reading. Fixing a car by changing part after part gets very expensive and isn't very efficient.

At what times does the idle problem occur? Engine cold/ warm?

As far as the dead spot, I'd start by checking the TPS with a voltmeter. Check that it has a good 5v reference, good ground, and that you are at .54 volts at idle. Move the TPS through its range, checking for any sudden jumps or flat spots.

 

The idle can change at any time but normally when warm , I have an OTC elite scanner and the only fault it show is 'air flow reading too high' the Air Flow test only appears to hit just over 100 when reved high , I thought it should go higher than that(near to 200) , and I have played with the TPS which was reading low 0.34v (idle), I got it up a bit(0.43v) but max I can get with throttle fully open is 3.14v , it should go just over 4v im told?
Also it is not showing any advance on the timing when reved , my buddy is bringing a timing light tomorrow to check it manually.

 

Your air flow (measured in grams / sec) will vary at a given point, but you should be at about 8 gr/sec at idle. For the moment, forget the MAF and work on the TPS issue, which is probably the cause of the error code your scantool shows.

Using a voltmeter, find the 5v reference to the TPS (don't recall if its blue or grey), and ground it. Make sure you are reading near 5 volts. Then, jumper the 5v reference wire and the black wire (ground), make sure you have a similar reading on your voltmeter. Should be near 5 volts.

If there is a problem with 5v or with ground, stop here and let me know.

If everything is fine to this point, and your max TPS voltage at full throttle is 3.14v, then the TPS is bad.

 

Daron,

Welcome Aboard!

Or, would that be "Welcome aboarrrrd, lad."

Sorry. Couldn't resist the temptation. You're allowed one free pass as a result.

As for the '85 TPI, yes, the control system is unique to that year. The general concepts are the same as with later TPI systems, but some of the parts are different.

Don't repeat what the previous owner apparently attempted. Evidently, he or she changed parts in an
attempt to solve a problem basded on "hunches" and with no regard to diagnosis. Given all the parts replaced, it would make little sense to replace them again.

If you start indescriminately replacing parts to find a solution, I may be tempted to swim over there, take the Guiness out of your hand, knock you down, and tell you not to do it again. We don't need to feed needless money to the aftermarket parts companies - They make plenty already. Besides, you'll have other things to do with your time if you read on.

Before spending $180 on a replacement MAF, spend about 1/3 of that on a good digital multimeter if you don't already have one. That will be one of the most important tools you will have in your diagnosis of the problem(s).

Regartding the MAF, the '85 TPI used a MAF sensor with a frequency modulated output. Later TPIs used a MAF with an analog voltage output. The end result is the same as far as the ECM is concerned, so unless you are getting error codes related to the MAF input, you can disregard that item for now. Even the older 1985 ECM was relatively into.erant of MAF errors, and would set a code within two seconds if the MAF input were out of the acceptable ranges. The only question is whether you are getting MAF error codes.

To assist us in locating the real problem, it would be good of you to scan for error codes. Although the 1985 ECM is not quite as robust as some later versions, it can still be useful in volunteering information. If you haven't already done so, scan the ECM for codes.

We can presume that the injectors are servicable, and they are identical to some of the later TPI injectors. So long as they are all connected, they should be fine. Given that the Cold Start Valve (injector) was replaced (probably at the same time) we'll presume that is good as well. Unless it is leaking, once the engine is running, it isn't a factor.

The new EGR valve is probably working fine, so long as it is the correct type. The universal replacement type valves don't always work well with TPI systems. If it is an OEM type, it should be good.

To my knowledge, there is no "EGT" sensor on a TPI, unless you are referring to the diagnostic temperature sensor attached to the EGR valve base. That would most likely have been replaced with the EGR valve, and would have no bearing on any misfire or idle hunting.

The brand new knock sensor will have little to do with it unless it is detecting false detonation. And the ESC mounted to the firewall could be a problem, but don't replace it without some testing. You can bypass the EST system (just as you would to set base timing) and eliminate the entire knock detection and EST from consideration. If the problems persist with the EST bypassed, the ESC and its knock sensor are probably not at fault.

The new Coolant Temperature Sensor (CTS/ECT) will not be a factor unless it is not connected properly. Again, the ECM would likely set an error code if this were the case.

A new TPS should eliminate any question of incorrect throttle angle data, so long as the circuit is connected properly.

The new O2 is always a good idea if the older sensor has been used for 30,000 miles or so, but again, it would have little bearing on idle wandering and misfire, especially on initial startup and warmup. The O² sensor isn't even used until the engine is warmed enough to allow closed loop mode.

The IAT has little relevance on the older TPI systems, but since you have a new one, it certainly can't hurt.

The new fuel pump and filter are good. The fuel pump is a difficult item to replace, and since it's been done for you, you shouldn't have to worry about it for quite some time. The replaced filter is also a good thing, since it removes another possibility from your potential list of problems.

As for the fuel system, the new pump and filter still do not gauranty correct fuel pressure and flow. The pressure regulator could still be a problem, and could be causing some of your problems. Again, don't simply replace it as a guess, but TEST it instead. Connect a fuel pressure gauge to the test fittin on the right fuel rail, start the engine, and monitor pressure. If the pressure is at 37 PSIG ± 3 PSIG with the engine running, and remains relatively stable, the regulator is probably good. With the engine running, you can remove the vacuum line to the pressure regulator. Upon doing that, the pressure should increase to 44 PSIG (3 Bar) ± 3 PSIG, and NO fuel should be leaking from the hose or regulator vacuum line. If everything checks out using those tests, the pressure regulator is working perfectly. Remove that from your list of suspects.

Using your digital meter, test the output voltage from that newly installed TPS. It may be new, but that doesn't mea it was installed correctly. If the output voltage is at 0.54 VDC ± 0.07 V with the throttle fully closed, it is set correctly. If the voltage is correct, move on to the next item.

The one item that is conspicuous by absence on your list is the Idle Air Control (IAC). If the throttle body, idle air passages, and IAC motor have not been given a thorough cleaning, it would be a good time to do that. While it may not affect the misfire to a large degree, it can solve a lot of the RPM hunting you are experiencing.

We'll wait here for you.

 

That's what I get for taking 20 minutes to author a reply...

 

It's all good...

 

It's good to see that you have a scanner at your disposal.

The TPS should be at least 0.47 VDC at the closed throttle position. The maximum at WOT is somewhat irrelevant. Although I haven't done any work with the older ECM programming, the later ECMs can consider any TPS voltage above 4.0 V as Wide Open Throttle. It is far more critical to get the idle position voltage correct.

The TPS voltage will affect what the ECM presumes about throttle angle, and your Code 33 (MAF flow too high) is almost always related to an incorrect TPS voltage, and always too low.

The F/M MAF sensor is about impossible to diagnose without a scanner or oscilloscope, so you're lucky to have the scanner at hand.

Incidentally, with the ECM reporting the MAF error, the system is running on Backup Fuel and Spark parameters, so the ESC will probably be inactive. That would explain the lack of advance beyond base timing.

Solve the TPS setting at closed throttle first, then proceed. If the TPS will not increase to at least 4.0V at WOT, we can address that later.

 

Thankyou for your help , as I live in Ireland we have no one here who works at these cars , but my friend is a head Landrover Technician and Landrover use V8 engines so he will do all the tests for me in the morning and i'll let you know what happens. Do you know what the timing settings should be?

 

Bypass the EST system (directions should be outlined on the VECI label under the hood) and set the base timing to 6° BTDC.

 

Update : My friend who is a head Landrover technician spent 3 hours today in his workshop testing the entire engine electrical system , the TPS was way off so he fixed that , also he manually checked the timing with a timing light and its perfect and is advancing as it should (don't know why thats not showing on the OTC Scanner) , he also made some adjustments to the throttle body and he is almost sure the ECM and MAF are fine , the car drove home very smoothe with no fluctuating idle and no flat spots so fingers crossed it seems to be cured , thanks to everyone who offered help , I am grateful .
Thanks

 

Another update : After my friend worked at the car last week it seemed to run well for a few days , but its back to its old ways again , the timing was checked and was correct and was advancing and the TPS is now giving the correct readings.
Now when I start it up the revs will settle at 800-900 for a few secs then it will drop to the verge of stalling and there is a huge flat spot on the first quarter of the pedal where it runs really rough like its off cylinders then if you floor it that will clear , also when I drove it today I floored it and the car took off then just died like it was really holding back , it really struggled then to go up a steep hill and my foot was to the floor.
It feels like something really simple but we just can't put our finger on it and there are limited resourses here in Ireland , can anyone help?
Could the ECM be faulty ? If so where can I get a new one? Will an ECM from a newer 86 on car run in my 85?

 

What are your fuel pressure readings on the car? In park at idle and with a load on the motor.

 

Good news , my friend and I have been working at the car for the past 4 hours , he noticed that the manifolds were glowing red hot which indicated to him that the exhaust gases were not flowing through , the exhaust is new but we took off the cat and took the guts out of it and put it back on hollow , also found one of the spark plug leads arcing on the manifold , fixed that and now the car is like a rocket , it has power it never had before , spins the wheels etc. So it seems that its fixed now, heres hoping!