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Performed a speed density TPI conversion on my '90 Formula 5.0 TBI/automatic. 7730 ECM with Scott Hansen chip AXXB (delete EGR test, delete VATS, delete AIR). Bosch III 19 lb injectors from SouthBay. New IAC, new temp sensors. TPS set to .54 v. When I run the minimum idle routine with the IAC disconnected (EST disconnected; base timing set to 6 degrees) the idle is not constant; surges and hunts. I used all new gaskets so I don't think there are any vacuum leaks, but I'm not sure what else would cause the surging idle. It's hard to set the base idle with it surging. After trying to set minimum idle and reconnecting IAC it will idle okay but not perfect. Not sure what to expect. Prior to TPI conversion it idled very smooth; almost couldn't tell it was running. The plugs, wires, distributor, etc. all were replaced when I did the header install last summer (about 600 miles ago). Running ALDL scan after minimum idle procedure shows IAC counts of 5-12 in gear and 0 in park. Seems pretty low, but I'm having a hard time finding target specifications (IAC, BLM, ect.) When I first drop into gear it almost stalls before settling at 600 rpm. Any input is appreciated.
Possible causes of the idle variation are EGR leakage, brake booster leakage, an incorrect PCV, or other internal vacuum/air leak. it would be easy to plug the PCV for testing, and cap off the brake booster vacuum hose, but not quite as easy to verify the EGR is fully shut.
Anyone know if I could pull the vacuum line to the EGR valve and plug the vacuum port under the throttle body, if that would tell me if I have the wrong type of EGR valve installed? I've read conflicting information about whether I should have a negative or positive back pressure EGR valve and so I installed the negative that I had. Perhaps it needs a positive back pressure EGR valve and that's causing my idle problems.
I doubt if your problem is associated with the wrong type of egr valve. One type of egr valve will open once the vacuum increases to a certain point and the solenoid is open. The other type of egr valve, I think positive pressure, opens only when the exhaust gas pressure increases to a certain point, along with the correct vacuum signal. If you do have a egr valve problem then maybe the valve has deposits that keeps it partially open. You should remove the egr and clean it. Also clean the passages in the intake manifold. Good luck.
Maybe these will help. Have you tried this from a cold start? i.e car sat over night? might help rule out something like O2 sensor, which doesn't kick in until it reaches certain temp
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Thanks, guys. I have ordered a new EGR valve (I re-used the old one that came on the TPI manifold I bought, hoping to save a few bucks; we all know how that usually turns out) just to make sure that variable is covered. I went through the minimum idle set procedure and that's when I discovered that the idle is unstable with the IAC disconnected. When I get the new EGR valve installed I'll try again. Kinda thinking now that I should have just had the EGR tuned out and slapped a plate on there.
Well, the EGR was definitely bad; runs better now. However, new problem: no TCC lockup. I did a data log and at 67 mph it shows TCC lock "0" and shift light "1". Does this mean it's signalling to shift? Does this mean the ECM thinks I have a manual transmission? Torque converter locked up fine prior to TPI/ECM swap.
Either the PROM is burned for a manual trans vehicle, or your scanner is not interpreting the the serial data steam correctly. The flag for TCC and shift light are from the same driver (I believe it may be A7 on the '730 ECM), but are applied differently in manual versus auto trans cars. On my scanners, I can enter data for the vehicle, and that helps set the parameters for its function and how it displays data.
You should verify whether the output is wired correctly for the auto, but if a complete ECM/harness swat was performed, it should be correct. You would also need to verify that the ECM has the 4th gear input wired and enabled.
Either the PROM is burned for a manual trans vehicle, or your scanner is not interpreting the the serial data steam correctly. The flag for TCC and shift light are from the same driver (I believe it may be A7 on the '730 ECM), but are applied differently in manual versus auto trans cars. On my scanners, I can enter data for the vehicle, and that helps set the parameters for its function and how it displays data.
You should verify whether the output is wired correctly for the auto, but if a complete ECM/harness swat was performed, it should be correct. You would also need to verify that the ECM has the 4th gear input wired and enabled.
Appreciate the input. Actually, it's A7 on the 8746 ECM and F6 on the 7730. I'm using the TBI harness with pin swap to 7730. I also removed the buffer box and ran purple and yellow to B9 and B10 (respectively) on the 7730; tan to B11 (instrument cluster) and red to C1 (cruise control).
Scott seemed to think that the VSS signal wasn't getting through to the ECM, but my data log shows accurate vehicle speed data on both runs I made. Cruise control works perfectly, too. He also told me to check the brake switch (which I'll do) but seems to me the cruise wouldn't operate if the brake switch was the problem. It seems to me that the ECM, for some unknown reason, is not commanding TCC lockup. He advised I get a TunerPro log to him so he can examine more closely whats happening and to also tune for better fuel curves (running pretty lean with BLM in 140-150 range). Unfortunately, I don't own a laptop. That's why I went with the 1320electronics bluetooth Android reader, but it's much more limited in what it can do.
it appears this ECM lacks the quad drivers necessary for TCC lockup. Really bummed; he told me to pull out the PROM and Memcal and send back the ECM and he would credit me $60. And I am officially dead in the water.
Installed my "new" ECM today and I now have TCC lockup. With the EGR problem fixed and the correct ECM installed, I can finally focus on tuning. Purchased ALDLDroid so I'll be able to do data logs that can be read in TunerPro. Anyone have any advise?
New problem. It seems that, according to my 1990 factory service manual, the TBI cars and TPI cars have different canister purge solenoids. The TBI (of which mine was one until the TPI conversion) purge solenoid is normally closed, so that it only opens when current is applied to the solenoid. The TPI cars are the opposite. Solenoid is normally open and closes with a current across the solenoid. I verified this by checking for current across the solenoid plug in my car with the 7730 ECM conversion; it shows 14.1 volts across the terminals at idle. Checked the canister that was on my TBI car and it opens with 12v applied. Which means that my canister purge valve is open at idle and would close when the ECM commands purge (the opposite that it needs). Can anyone confirm this and, more importantly, know where I can get a correct solenoid? I have searched and not found anything.
I've never researched this, but if it is true, the solenoid operation can be inverted using a small relay. Let the ECM output ground the relay coil just as it would the EVAP solenoid, and source the relay coil with IGN or GAGE power. Let the relay NC contacts ground the TBI-type solenoid.
That could be a solution if you cannot source the correct EVAP solenoid valve.
I've never researched this, but if it is true, the solenoid operation can be inverted using a small relay. Let the ECM output ground the relay coil just as it would the EVAP solenoid, and source the relay coil with IGN or GAGE power. Let the relay NC contacts ground the TBI-type solenoid.
That could be a solution if you cannot source the correct EVAP solenoid valve.
Ha! Great minds think alike. This was my Plan B and after some thought, decided to promote to Plan A. For one thing, I don't have to worry about a 25-30 year-old part in there that is energized most of the time. And the relay, which will be energized most of the time, will be a new, inexpensive and common part.
Any progress finding the cause of the surge ?
As brought up in another tpi thread often overlooked is a internal vacuum leak from the brake booster. Since it surges with the iac unplugged you can block the line with a bolt or your thumb and see if the surging goes away.
Any progress finding the cause of the surge ?
As brought up in another tpi thread often overlooked is a internal vacuum leak from the brake booster. Since it surges with the iac unplugged you can block the line with a bolt or your thumb and see if the surging goes away.
I think I'm gonna try that. I have noticed that the idle changes ever so slightly when I hit the brake pedal. Not sure if that's normal or not. It idles solid in gear (and warmed up). Haven't been able to do a log run on this third memcal yet. I hate it when work gets in the way of my hobby!
Well, I learned something yesterday. SD TPI uses different PCV valve than TBI. Picked up a 1990-92 TPI PCV valve and installed. Ran minimum idle routine and had to open the throttle blades quite a bit to get minimum specified idle speed, probably 3/4 to full turn of idle stop screw. Only thing I changed was the PCV valve, so I think it was affecting my idle (at least). Now if I could just get a usable data log run...!
Just to follow up: idle seems to be good to go now. Between replacing the EGR valve (and solenoid) and PCV valve, idle has stabilized. Does anyone have any solid idea as to what base timing I should set this thing? It's got TBI heads/cam with TPI intake and Hooker shorties. I know TPI specs 6 degrees and TBI specs 0 degrees. I compromised and set it at 4, but I still get 2-6 degrees of knock retard at times. I think the early tunes were lean, so I attributed the knock retard to that, but the last tune was a bit rich (BLM ~120) and I still got knock retard. Is some knock retard normal? Running 91 octane "real" gas (which is premium here at ~1,100 ft altitude). FWIW, this is a ~18,000 mile engine that, when I pulled the intake and valve covers, looked amazingly clean, so I wouldn't expect there to be significant carbon build-up. I can't really hear any knock, but my 60-year-old ears aren't what they used to be either.
01-19-2019, 09:09 AM
