Howell TBI conversion on FJ40- Troubleshooting

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Feb 26, 2018
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This last year, I did a TBI conversion on my FJ. The conversion that Howell does is from an early 90’s chevy. I have had a series of issues with the conversion and for the money I’ve put into it trying to get it to run properly, I could have dropped a 350 in. But I digress...
I’ve ran the system and even paid a Custom shop to re-run the system, and keep having cut out issues. Runs pretty rich. Idles okay but as soon as it warms up, cuts out like crazy. Put a high performance distributer on, re-did timing, re-replaced the o2 sensor, re-did the plugs and wires, cleaned the filter. I then decided to get a fuel pressure check kit and found that the fuel pump is running at about 16. It’s my understanding from Howell that it should run at 12. Could high fuel pressure cause it to cut out when excelerating?? Please help
 
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Sounds like it's messing up when going to closed loop.
So yes your FP is too high.
How is your ECT?
is your exhaust sealed up properly? How well does the motor actually run, meaning actually getting good combustion. I recently worked on an aftermarket kit that was giving issues once warmed up. Turned out it had bad ignition parts but was also just kind of a weak motor. It was getting incomplete combustion from the wear etc and was showing the oxygen sensor more oxygen than it should causing a constant enrichment issue with the efi.
 
Joined
Feb 26, 2018
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Pretty sure ECT is good. I also checked and topped off coolant because I heard the temp can really mess with that kit. Also pretty sure the motor is good. Rebuilt it about 10k miles ago. Do you think it would be best to replace the pump or just through on a pressure regulator?
 
Joined
Oct 11, 2004
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211
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sc/nc
 
I know you say it has been installed correctly but what have you done/checked?
TPS setting/reading, map sensor, what port on the tbi is the map sensor connected to? Heated o2? Vacuum leaks? Fuel lines? Is there restriction in you return? Cel? Does it work? Any stored codes? Have you run it hooked to a scanner? Can you see what the computer is reading in real time?
Rochester tbi is pretty simpl and fool proof. If you could give some more information on what you have checked I might be able to help you troubleshoot.
 
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I haven’t tried replacing the TPS. Actually no sure how to gather a reading on that. The shop checked and double checked for leaks, none. No fuel leaks. As of now, no stored codes.
Block learn 130
123 at idle
123 at cruise (Which are all correct)
When I spoke with Howell, they mentioned that even a 2psi difference in fuel pressure will creat big issues. I wasn’t sure what the result generally is when fuel pressure is too high (other than running rich). I’ll have to go out tomorrow and get some pictures to upload.
 
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Feb 19, 2004
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Pepperell MA
 
 
 
High fuel pressure will cause it to run rich. A bad or not properly connected MAP sensor will also cause it to run way rich (BTDT on a TBI converted Cruiser I had years ago...).

Nick
 
Joined
Oct 11, 2004
Messages
211
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sc/nc
 
Check reading on tps. Ball park .5volts closed, 4-5volts wot. I had a tbi In a new conversion that had the correct style tps, but the tps read backwards. It showed 5 volts closed and .5 at wot. Did not take that long to figure out but took a minute to find the correct tps not knowing what the tbi was from.
Where is the vacuum line to your map sensor connected? It goes on the back of the tbi between the inlet and return fuel fittings.
Pcv goes to the front.
 
Joined
Oct 11, 2004
Messages
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sc/nc
 
16 psi is to the high end but completely managed by the tbi fuel pressure regulator. I would check map sensor and tps.
Also check the prom chips. Make sure they are fully seated or installed on the board.
 
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Oct 11, 2004
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sc/nc
 
Depending on the parts you receive you may have to have a few different hose sizes to go from the nipple on the map sensor to the port on the throttle body. I have seen the map sensor run to the pcv port on the front of the tbi many times, just because the hose fit the best there. It will not run right in that location.
 
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Heavytlc,
Update:
I tried the MAP sensor first. Turns out it was ran exactly like you suspected. I disconnected and ran to the throttle body port and even with a loose connection, it fixed most of the issues I was having. I’ll reduce to a smaller size, see how it runs and then test the TPS wires. If we ever meet, I’ll owe you lunch. Thanks for the pointers.
 
Joined
Jun 8, 2008
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San Diego
 
 
Heavytlc,
Update:
I tried the MAP sensor first. Turns out it was ran exactly like you suspected. I disconnected and ran to the throttle body port and even with a loose connection, it fixed most of the issues I was having. I’ll reduce to a smaller size, see how it runs and then test the TPS wires. If we ever meet, I’ll owe you lunch. Thanks for the pointers.
Awesome, congratulations! Thanks for reporting back, it might help others. Great job Heavytlc!
 
Joined
Oct 11, 2004
Messages
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sc/nc
 
I am glad I could help. Like most things that are 35 years old, the ability to troubleshoot and understand rochester TBI is becoming a dying art. I did my first tbi 350 in a fj40 in 94/95. I have always had a couple of either stock chevrolets or swapped fj40's in my daily driver rotation.
Your kit probably has the late model map sensor. It is an improved design. when you mount it it needs to have the nipple pointing down. It was how it was designed to mount and they give a much longer service life mounted that way.
In the help section of just about any parts store the will have vacuum tubing adaptor/couplers. Just a small plastic piece with 2 different size barbs at each end. makes quick work of getting the hoses to fit at each end.
 
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